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1.  Sleep-Disordered Breathing and Mortality: A Prospective Cohort Study 
PLoS Medicine  2009;6(8):e1000132.
In a cohort of 6,441 volunteers followed over an average of 8.2 years, Naresh Punjabi and colleagues find sleep-disordered breathing to be independently associated with mortality and identify predictive characteristics.
Background
Sleep-disordered breathing is a common condition associated with adverse health outcomes including hypertension and cardiovascular disease. The overall objective of this study was to determine whether sleep-disordered breathing and its sequelae of intermittent hypoxemia and recurrent arousals are associated with mortality in a community sample of adults aged 40 years or older.
Methods and Findings
We prospectively examined whether sleep-disordered breathing was associated with an increased risk of death from any cause in 6,441 men and women participating in the Sleep Heart Health Study. Sleep-disordered breathing was assessed with the apnea–hypopnea index (AHI) based on an in-home polysomnogram. Survival analysis and proportional hazards regression models were used to calculate hazard ratios for mortality after adjusting for age, sex, race, smoking status, body mass index, and prevalent medical conditions. The average follow-up period for the cohort was 8.2 y during which 1,047 participants (587 men and 460 women) died. Compared to those without sleep-disordered breathing (AHI: <5 events/h), the fully adjusted hazard ratios for all-cause mortality in those with mild (AHI: 5.0–14.9 events/h), moderate (AHI: 15.0–29.9 events/h), and severe (AHI: ≥30.0 events/h) sleep-disordered breathing were 0.93 (95% CI: 0.80–1.08), 1.17 (95% CI: 0.97–1.42), and 1.46 (95% CI: 1.14–1.86), respectively. Stratified analyses by sex and age showed that the increased risk of death associated with severe sleep-disordered breathing was statistically significant in men aged 40–70 y (hazard ratio: 2.09; 95% CI: 1.31–3.33). Measures of sleep-related intermittent hypoxemia, but not sleep fragmentation, were independently associated with all-cause mortality. Coronary artery disease–related mortality associated with sleep-disordered breathing showed a pattern of association similar to all-cause mortality.
Conclusions
Sleep-disordered breathing is associated with all-cause mortality and specifically that due to coronary artery disease, particularly in men aged 40–70 y with severe sleep-disordered breathing.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
About 1 in 10 women and 1 in 4 men have a chronic condition called sleep-disordered breathing although most are unaware of their problem. Sleep-disordered breathing, which is commonest in middle-aged and elderly people, is characterized by numerous, brief (10 second or so) interruptions of breathing during sleep. These interruptions, which usually occur when relaxation of the upper airway muscles decreases airflow, lower the level of oxygen in the blood and, as a result, affected individuals are frequently aroused from deep sleep as they struggle to breathe. Symptoms of sleep-disordered breathing include loud snoring and daytime sleepiness. Treatments include lifestyle changes such as losing weight (excess fat around the neck increases airway collapse) and smoking cessation. Affected people can also use special devices to prevent them sleeping on their backs, but for severe sleep-disordered breathing, doctors often recommend continuous positive airway pressure (CPAP), a machine that pressurizes the upper airway through a face mask to keep it open.
Why Was This Study Done?
Sleep-disordered breathing is a serious condition. It is associated with several adverse health conditions including coronary artery disease (narrowing of the blood vessels that supply the heart, a condition that can cause a heart attack) and daytime sleepiness that can affect an individual's driving ability. In addition, several clinic- and community-based studies suggest that sleep-disordered sleeping may increase a person's risk of dying. However, because these studies have been small and have often failed to allow for other conditions and characteristics that affect an individual's risk of dying (“confounding factors”), they provide inconsistent or incomplete information about the potential association between sleep-disordered breathing and the risk of death. In this prospective cohort study (part of the Sleep Heart Health Study, which is researching the effects of sleep-disordered breathing on cardiovascular health), the researchers examine whether sleep-disordered breathing is associated with all-cause mortality (death from any cause) in a large community sample of adults. A prospective cohort study is one in which a group of participants is enrolled and then followed forward in time (in this case for several years) to see what happens to them.
What Did the Researchers Do and Find?
At enrollment, the study participants—more than 6,000 people aged 40 years or older, none of whom were being treated for sleep-disordered breathing—had a health examination. Their night-time breathing, sleep patterns, and blood oxygen levels were also assessed and these data used to calculate each participant's apnea-hypopnea index (AHI)—the number of apneas and hypopneas per hour. During the study follow-up period, 1,047 participants died. Compared to participants without sleep-disordered sleeping, participants with severe sleep-disordered breathing (an AHI of ≥30) were about one and a half times as likely to die from any cause after adjustment for potential confounding factors. People with milder sleep-disordered breathing did not have a statistically significant increased risk of dying. After dividing the participants into subgroups according to their age and sex, men aged 40–70 years with severe sleep-disordered breathing had a statistically increased risk of dying from any cause (twice the risk of men of a similar age without sleep-disordered breathing). Finally, death from coronary artery disease was also associated with sleep-disordered breathing in men but not in women.
What Do These Findings Mean?
These findings indicate that sleep-disordered breathing is associated with an increased risk of all-cause mortality, particularly in men aged 40–70 years, even after allowing for known confounding factors. They also suggest that the increased risk of death is specifically associated with coronary artery disease although further studies are needed to confirm this finding because it was based on the analysis of a small subgroup of study participants. Although this study is much larger than previous investigations into the association between sleep-disordered breathing and all-cause mortality, it has several limitations including its reliance on a single night's measurements for the diagnosis of sleep-disordered breathing. Nevertheless, these findings suggest that clinical trials should now be started to assess whether treatment can reduce the increased risk of death that seems to be associated with this common disorder.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000132.
The US National Heart Lung and Blood Institute has information (including a video) about sleep-disordered breathing (sleep apnea) (in English and Spanish)
The UK National Heath Service also provides information for patients about sleep apnea
MedlinePlus provides links to further information and advice about sleep-disordered breathing (in English and Spanish)
More information on the Sleep Heart Health Study is available
doi:10.1371/journal.pmed.1000132
PMCID: PMC2722083  PMID: 19688045
2.  Polysomnography in Patients With Obstructive Sleep Apnea 
Executive Summary
Objective
The objective of this health technology policy assessment was to evaluate the clinical utility and cost-effectiveness of sleep studies in Ontario.
Clinical Need: Target Population and Condition
Sleep disorders are common and obstructive sleep apnea (OSA) is the predominant type. Obstructive sleep apnea is the repetitive complete obstruction (apnea) or partial obstruction (hypopnea) of the collapsible part of the upper airway during sleep. The syndrome is associated with excessive daytime sleepiness or chronic fatigue. Several studies have shown that OSA is associated with hypertension, stroke, and other cardiovascular disorders; many researchers believe that these cardiovascular disorders are consequences of OSA. This has generated increasing interest in recent years in sleep studies.
The Technology Being Reviewed
There is no ‘gold standard’ for the diagnosis of OSA, which makes it difficult to calibrate any test for diagnosis. Traditionally, polysomnography (PSG) in an attended setting (sleep laboratory) has been used as a reference standard for the diagnosis of OSA. Polysomnography measures several sleep variables, one of which is the apnea-hypopnea index (AHI) or respiratory disturbance index (RDI). The AHI is defined as the sum of apneas and hypopneas per hour of sleep; apnea is defined as the absence of airflow for ≥ 10 seconds; and hypopnea is defined as reduction in respiratory effort with ≥ 4% oxygen desaturation. The RDI is defined as the sum of apneas, hypopneas, and abnormal respiratory events per hour of sleep. Often the two terms are used interchangeably. The AHI has been widely used to diagnose OSA, although with different cut-off levels, the basis for which are often unclear or arbitrarily determined. Generally, an AHI of more than five events per hour of sleep is considered abnormal and the patient is considered to have a sleep disorder. An abnormal AHI accompanied by excessive daytime sleepiness is the hallmark for OSA diagnosis. For patients diagnosed with OSA, continuous positive airway pressure (CPAP) therapy is the treatment of choice. Polysomnography may also used for titrating CPAP to individual needs.
In January 2005, the College of Physicians and Surgeons of Ontario published the second edition of Independent Health Facilities: Clinical Practice Parameters and Facility Standards: Sleep Medicine, commonly known as “The Sleep Book.” The Sleep Book states that OSA is the most common primary respiratory sleep disorder and a full overnight sleep study is considered the current standard test for individuals in whom OSA is suspected (based on clinical signs and symptoms), particularly if CPAP or surgical therapy is being considered.
Polysomnography in a sleep laboratory is time-consuming and expensive. With the evolution of technology, portable devices have emerged that measure more or less the same sleep variables in sleep laboratories as in the home. Newer CPAP devices also have auto-titration features and can record sleep variables including AHI. These devices, if equally accurate, may reduce the dependency on sleep laboratories for the diagnosis of OSA and the titration of CPAP, and thus may be more cost-effective.
Difficulties arise, however, when trying to assess and compare the diagnostic efficacy of in-home PSG versus in-lab. The AHI measured from portable devices in-home is the sum of apneas and hypopneas per hour of time in bed, rather than of sleep, and the absolute diagnostic efficacy of in-lab PSG is unknown. To compare in-home PSG with in-lab PSG, several researchers have used correlation coefficients or sensitivity and specificity, while others have used Bland-Altman plots or receiver operating characteristics (ROC) curves. All these approaches, however, have potential pitfalls. Correlation coefficients do not measure agreement; sensitivity and specificity are not helpful when the true disease status is unknown; and Bland-Altman plots measure agreement (but are helpful when the range of clinical equivalence is known). Lastly, receiver operating characteristics curves are generated using logistic regression with the true disease status as the dependent variable and test values as the independent variable. Thus, each value of the test is used as a cut-point to measure sensitivity and specificity, which are then plotted on an x-y plane. The cut-point that maximizes both sensitivity and specificity is chosen as the cut-off level to discriminate between disease and no-disease states. In the absence of a gold standard to determine the true disease status, ROC curves are of minimal value.
At the request of the Ontario Health Technology Advisory Committee (OHTAC), MAS has thus reviewed the literature on PSG published over the last two years to examine new developments.
Methods
Review Strategy
There is a large body of literature on sleep studies and several reviews have been conducted. Two large cohort studies, the Sleep Heart Health Study and the Wisconsin Sleep Cohort Study, are the main sources of evidence on sleep literature.
To examine new developments on PSG published in the past two years, MEDLINE, EMBASE, MEDLINE In-Process & Other Non-Indexed Citations, the Cochrane Database of Systematic Reviews and Cochrane CENTRAL, INAHTA, and websites of other health technology assessment agencies were searched. Any study that reported results of in-home or in-lab PSG was included. All articles that reported findings from the Sleep Heart Health Study and the Wisconsin Sleep Cohort Study were also reviewed.
Diffusion of Sleep Laboratories
To estimate the diffusion of sleep laboratories, a list of sleep laboratories licensed under the Independent Health Facility Act was obtained. The annual number of sleep studies per 100,000 individuals in Ontario from 2000 to 2004 was also estimated using administrative databases.
Summary of Findings
Literature Review
A total of 315 articles were identified that were published in the past two years; 227 were excluded after reviewing titles and abstracts. A total of 59 articles were identified that reported findings of the Sleep Heart Health Study and the Wisconsin Sleep Cohort Study.
Prevalence
Based on cross-sectional data from the Wisconsin Sleep Cohort Study of 602 men and women aged 30 to 60 years, it is estimated that the prevalence of sleep-disordered breathing is 9% in women and 24% in men, on the basis of more than five AHI events per hour of sleep. Among the women with sleep disorder breathing, 22.6% had daytime sleepiness and among the men, 15.5% had daytime sleepiness. Based on this, the prevalence of OSA in the middle-aged adult population is estimated to be 2% in women and 4% in men.
Snoring is present in 94% of OSA patients, but not all snorers have OSA. Women report daytime sleepiness less often compared with their male counterparts (of similar age, body mass index [BMI], and AHI). Prevalence of OSA tends to be higher in older age groups compared with younger age groups.
Diagnostic Value of Polysomnography
It is believed that PSG in the sleep laboratory is more accurate than in-home PSG. In the absence of a gold standard, however, claims of accuracy cannot be substantiated. In general, there is poor correlation between PSG variables and clinical variables. A variety of cut-off points of AHI (> 5, > 10, and > 15) are arbitrarily used to diagnose and categorize severity of OSA, though the clinical importance of these cut-off points has not been determined.
Recently, a study of the use of a therapeutic trial of CPAP to diagnose OSA was reported. The authors studied habitual snorers with daytime sleepiness in the absence of other medical or psychiatric disorders. Using PSG as the reference standard, the authors calculated the sensitivity of this test to be 80% and its specificity to be 97%. Further, they concluded that PSG could be avoided in 46% of this population.
Obstructive Sleep Apnea and Obesity
Obstructive sleep apnea is strongly associated with obesity. Obese individuals (BMI >30 kg/m2) are at higher risk for OSA compared with non-obese individuals and up to 75% of OSA patients are obese. It is hypothesized that obese individuals have large deposits of fat in the neck that cause the upper airway to collapse in the supine position during sleep. The observations reported from several studies support the hypothesis that AHIs (or RDIs) are significantly reduced with weight loss in obese individuals.
Obstructive Sleep Apnea and Cardiovascular Diseases
Associations have been shown between OSA and comorbidities such as diabetes mellitus and hypertension, which are known risk factors for myocardial infarction and stroke. Patients with more severe forms of OSA (based on AHI) report poorer quality of life and increased health care utilization compared with patients with milder forms of OSA. From animal models, it is hypothesized that sleep fragmentation results in glucose intolerance and hypertension. There is, however, no evidence from prospective studies in humans to establish a causal link between OSA and hypertension or diabetes mellitus. It is also not clear that the associations between OSA and other diseases are independent of obesity; in most of these studies, patients with higher values of AHI had higher values of BMI compared with patients with lower AHI values.
A recent meta-analysis of bariatric surgery has shown that weight loss in obese individuals (mean BMI = 46.8 kg/m2; range = 32.30–68.80) significantly improved their health profile. Diabetes was resolved in 76.8% of patients, hypertension was resolved in 61.7% of patients, hyperlipidemia improved in 70% of patients, and OSA resolved in 85.7% of patients. This suggests that obesity leads to OSA, diabetes, and hypertension, rather than OSA independently causing diabetes and hypertension.
Health Technology Assessments, Guidelines, and Recommendations
In April 2005, the Centers for Medicare and Medicaid Services (CMS) in the United States published its decision and review regarding in-home and in-lab sleep studies for the diagnosis and treatment of OSA with CPAP. In order to cover CPAP, CMS requires that a diagnosis of OSA be established using PSG in a sleep laboratory. After reviewing the literature, CMS concluded that the evidence was not adequate to determine that unattended portable sleep study was reasonable and necessary in the diagnosis of OSA.
In May 2005, the Canadian Coordinating Office of Health Technology Assessment (CCOHTA) published a review of guidelines for referral of patients to sleep laboratories. The review included 37 guidelines and associated reviews that covered 18 applications of sleep laboratory studies. The CCOHTA reported that the level of evidence for many applications was of limited quality, that some cited studies were not relevant to the recommendations made, that many recommendations reflect consensus positions only, and that there was a need for more good quality studies of many sleep laboratory applications.
Diffusion
As of the time of writing, there are 97 licensed sleep laboratories in Ontario. In 2000, the number of sleep studies performed in Ontario was 376/100,000 people. There was a steady rise in sleep studies in the following years such that in 2004, 769 sleep studies per 100,000 people were performed, for a total of 96,134 sleep studies. Based on prevalence estimates of the Wisconsin Sleep Cohort Study, it was estimated that 927,105 people aged 30 to 60 years have sleep-disordered breathing. Thus, there may be a 10-fold rise in the rate of sleep tests in the next few years.
Economic Analysis
In 2004, approximately 96,000 sleep studies were conducted in Ontario at a total cost of ~$47 million (Cdn). Since obesity is associated with sleep disordered breathing, MAS compared the costs of sleep studies to the cost of bariatric surgery. The cost of bariatric surgery is $17,350 per patient. In 2004, Ontario spent $4.7 million per year for 270 patients to undergo bariatric surgery in the province, and $8.2 million for 225 patients to seek out-of-country treatment. Using a Markov model, it was concluded that shifting costs from sleep studies to bariatric surgery would benefit more patients with OSA and may also prevent health consequences related to diabetes, hypertension, and hyperlipidemia. It is estimated that the annual cost of treating comorbid conditions in morbidly obese patients often exceeds $10,000 per patient. Thus, the downstream cost savings could be substantial.
Considerations for Policy Development
Weight loss is associated with a decrease in OSA severity. Treating and preventing obesity would also substantially reduce the economic burden associated with diabetes, hypertension, hyperlipidemia, and OSA. Promotion of healthy weights may be achieved by a multisectorial approach as recommended by the Chief Medical Officer of Health for Ontario. Bariatric surgery has the potential to help morbidly obese individuals (BMI > 35 kg/m2 with an accompanying comorbid condition, or BMI > 40 kg/m2) lose weight. In January 2005, MAS completed an assessment of bariatric surgery, based on which OHTAC recommended an improvement in access to these surgeries for morbidly obese patients in Ontario.
Habitual snorers with excessive daytime sleepiness have a high pretest probability of having OSA. These patients could be offered a therapeutic trial of CPAP to diagnose OSA, rather than a PSG. A majority of these patients are also obese and may benefit from weight loss. Individualized weight loss programs should, therefore, be offered and patients who are morbidly obese should be offered bariatric surgery.
That said, and in view of the still evolving understanding of the causes, consequences and optimal treatment of OSA, further research is warranted to identify which patients should be screened for OSA.
PMCID: PMC3379160  PMID: 23074483
3.  Increased Cerebral Blood Flow Velocity in Children with Mild Sleep-Disordered Breathing 
Pediatrics  2006;118(4):e1100-e1108.
Objective
Sleep-disordered breathing describes a spectrum of upper airway obstruction in sleep from simple primary snoring, estimated to affect 10% of preschool children, to the syndrome of obstructive sleep apnea. Emerging evidence has challenged previous assumptions that primary snoring is benign. A recent report identified reduced attention and higher levels of social problems and anxiety/depressive symptoms in snoring children compared with controls. Uncertainty persists regarding clinical thresholds for medical or surgical intervention in sleep-disordered breathing, underlining the need to better understand the pathophysiology of this condition. Adults with sleep-disordered breathing have an increased risk of cerebrovascular disease independent of atherosclerotic risk factors. There has been little focus on cerebrovascular function in children with sleep-disordered breathing, although this would seem an important line of investigation, because studies have identified abnormalities of the systemic vasculature. Raised cerebral blood flow velocities on transcranial Doppler, compatible with raised blood flow and/or vascular narrowing, are associated with neuropsychological deficits in children with sickle cell disease, a condition in which sleep-disordered breathing is common. We hypothesized that there would be cerebral blood flow velocity differences in sleep-disordered breathing children without sickle cell disease that might contribute to the association with neuropsychological deficits.
Design
Thirty-one snoring children aged 3 to 7 years were recruited from adenotonsillectomy waiting lists, and 17 control children were identified through a local Sunday school or as siblings of cases. Children with craniofacial abnormalities, neuromuscular disorders, moderate or severe learning disabilities, chronic respiratory/cardiac conditions, or allergic rhinitis were excluded. Severity of sleep-disordered breathing in snoring children was categorized by attended polysomnography. Weight, height, and head circumference were measured in all of the children. BMI and occipitofrontal circumference z scores were computed. Resting systolic and diastolic blood pressure were obtained. Both sleep-disordered breathing children and the age- and BMI-similar controls were assessed using the Behavior Rating Inventory of Executive Function (BRIEF), Neuropsychological Test Battery for Children (NEPSY) visual attention and visuomotor integration, and IQ assessment (Wechsler Preschool and Primary Scale of Intelligence Version III). Transcranial Doppler was performed using a TL2-64b 2-MHz pulsed Doppler device between 2 PM and 7 PM in all of the patients and the majority of controls while awake. Time-averaged mean of the maximal cerebral blood flow velocities was measured in the left and right middle cerebral artery and the higher used for analysis.
Results
Twenty-one snoring children had an apnea/hypopnea index <5, consistent with mild sleep-disordered breathing below the conventional threshold for surgical intervention. Compared with 17 nonsnoring controls, these children had significantly raised middle cerebral artery blood flow velocities. There was no correlation between cerebral blood flow velocities and BMI or systolic or diastolic blood pressure indices. Exploratory analyses did not reveal any significant associations with apnea/hypopnea index, apnea index, hypopnea index, mean pulse oxygen saturation, lowest pulse oxygen saturation, accumulated time at pulse oxygen saturation <90%, or respiratory arousals when examined in separate bivariate correlations or in aggregate when entered simultaneously. Similarly, there was no significant association between cerebral blood flow velocities and parental estimation of child’s exposure to sleep-disordered breathing. However, it is important to note that whereas the sleep-disordered breathing group did not exhibit significant hypoxia at the time of study, it was unclear to what extent this may have been a feature of their sleep-disordered breathing in the past. IQ measures were in the average range and comparable between groups. Measures of processing speed and visual attention were significantly lower in sleep-disordered breathing children compared with controls, although within the average range. There were similar group differences in parental-reported executive function behavior. Although there were no direct correlations, adjusting for cerebral blood flow velocities eliminated significant group differences between processing speed and visual attention and decreased the significance of differences in Behavior Rating Inventory of Executive Function scores, suggesting that cerebral hemodynamic factors contribute to the relationship between mild sleep-disordered breathing and these outcome measures.
Conclusions
Cerebral blood flow velocities measured by noninvasive transcranial Doppler provide evidence for increased cerebral blood flow and/or vascular narrowing in childhood sleep-disordered breathing; the relationship with neuropsychological deficits requires further exploration. A number of physiologic changes might alter cerebral blood flow and/or vessel diameter and, therefore, affect cerebral blood flow velocities. We were able to explore potential confounding influences of obesity and hypertension, neither of which explained our findings. Second, although cerebral blood flow velocities increase with increasing partial pressure of carbon dioxide and hypoxia, it is unlikely that the observed differences could be accounted for by arterial blood gas tensions, because all of the children in the study were healthy, with no cardiorespiratory disease, other than sleep-disordered breathing in the snoring group. Although arterial partial pressure of oxygen and partial pressure of carbon dioxide were not monitored during cerebral blood flow velocity measurement, assessment was undertaken during the afternoon/early evening when the child was awake, and all of the sleep-disordered breathing children had normal resting oxyhemoglobin saturation at the outset of their subsequent sleep studies that day. Finally, there is an inverse linear relationship between cerebral blood flow and hematocrit in adults, and it is known that iron-deficient erythropoiesis is associated with chronic infection, such as recurrent tonsillitis, a clinical feature of many of the snoring children in the study. Preoperative full blood counts were not performed routinely in these children, and, therefore, it was not possible to exclude anemia as a cause of increased cerebral blood flow velocity in the sleep-disordered breathing group. However, hemoglobin levels were obtained in 4 children, 2 of whom had borderline low levels (10.9 and 10.2 g/dL). Although there was no apparent relationship with cerebral blood flow velocity in these children (cerebral blood flow velocity values of 131 and 130 cm/second compared with 130 and 137 cm/second in the 2 children with normal hemoglobin levels), this requires verification. It is of particular interest that our data suggest a relationship among snoring, increased cerebral blood flow velocities and indices of cognition (processing speed and visual attention) and perhaps behavioral (Behavior Rating Inventory of Executive Function) function. This finding is preliminary: a causal relationship is not established, and the physiologic mechanisms underlying such a relationship are not clear. Prospective studies that quantify cumulative exposure to the physiologic consequences of sleep-disordered breathing, such as hypoxia, would be informative.
doi:10.1542/peds.2006-0092
PMCID: PMC1995426  PMID: 17015501
sleep disordered breathing; cerebral blood flow; transcranial Doppler; executive function; neuropsychological function
4.  Sleep disorders in children 
Clinical Evidence  2010;2010:2304.
Introduction
Sleep disorders may affect between 20% and 30% of young children, and include problems getting to sleep (dyssomnias), or undesirable phenomena during sleep (parasomnias), such as sleep terrors and sleepwalking. Children with physical or learning disabilities are at increased risk of sleep disorders.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of treatments for dyssomnias in children? What are the effects of treatments for parasomnias in children? We searched: Medline, Embase, The Cochrane Library, and other important databases up to September 2009 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 28 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review we present information relating to the effectiveness and safety of the following interventions: antihistamines; behavioural therapy plus antihistamines, plus benzodiazepines, or plus chloral and derivatives; benzodiazepines alone; exercise; extinction and graduated extinction; 5-hydroxytryptophan; light therapy; melatonin; safety/protective interventions for parasomnias; scheduled waking (for parasomnias); sleep hygiene; and sleep restriction.
Key Points
Sleep disorders may affect between 20% and 30% of young children, and include problems getting to sleep (dyssomnias) or undesirable phenomena during sleep (parasomnias), such as sleep terrors and sleepwalking. Children with physical or learning disabilities are at increased risk of sleep disorders. Other risk factors include the child being the first born, having a difficult temperament or having had colic, and increased maternal responsiveness.
There is a paucity of evidence about effective treatments for sleep disorders in children, especially parasomnias, but behavioural interventions may be the best first-line approach.
Extinction and graduated extinction in otherwise healthy children with dyssomnia may improve sleep quality and settling, and reduce the number of tantrums and wakenings compared with no treatment. Extinction and graduated extinction in children with physical disabilities, learning disabilities, epilepsy, or attention-deficit disorder with dyssomnia may be more effective at improving settling, reducing the frequency and duration of night wakings, and improving parental sleep compared with no treatment; however, we don't know whether it is more effective in improving sleep duration.Graduated extinction may be less distressing for parents, and therefore may have better compliance.
Sleep hygiene for dyssomnia in otherwise healthy children may be more effective in reducing the number and duration of bedtime tantrums compared with placebo, but we don’t know if it is more effective at reducing night wakenings, improving sleep latency, improving total sleep duration, or improving maternal mood. Sleep hygiene and graduated extinction seem to be equally effective at reducing bedtime tantrums in otherwise healthy children with dyssomnia.We don't know whether sleep hygiene for dyssomnia in children with physical disabilities, learning disabilities, epilepsy, or attention-deficit disorder is effective.
Melatonin for dyssomnia in otherwise healthy children may be more effective at improving sleep-onset time, total sleep time, and general health compared with placebo. Evidence of improvements in dyssomnia with melatonin is slightly stronger in children with physical disabilities, learning disabilities, epilepsy, or attention-deficit disorder.
Little is known about the long-term effects of melatonin, and the quality of the product purchased could be variable as melatonin is classified as a food supplement.
Antihistamines for dyssomnia may be more effective than placebo at reducing night wakenings and decreasing sleep latency, but we don’t know if they are more effective at increasing sleep duration. The evidence for antihistamines in dyssomnia comes from only one small, short-term study.
We don’t know whether behavioural therapy plus antihistamines, plus benzodiazepines, or plus chloral and derivatives, exercise, light therapy, or sleep restriction are effective in children with dyssomnia.
We don’t know whether antihistamines, behavioural therapy plus benzodiazepines or plus chloral and derivatives, benzodiazepines, 5-hydroxytryptophan, melatonin, safety/protective interventions, scheduled waking, sleep hygiene, or sleep restriction are effective in children with parasomnia.
PMCID: PMC3217667  PMID: 21418676
5.  Sleep Dysfunction and Thalamic Abnormalities in Adolescents at Ultra High-Risk for Psychosis 
Schizophrenia research  2013;151(0):10.1016/j.schres.2013.09.015.
Background
Sleep dysfunction is a pervasive, distressing characteristic of psychosis, yet little is known regarding sleep quality prior to illness onset. At present, it is unclear whether sleep dysfunction precedes the emergence of psychotic symptoms, signifying a core feature of the disorder, or if it represents a consequence of prolonged contact with aspects of schizophrenia and its treatment (e.g., medication use or neurotoxicity) or co-morbid symptoms (e.g., depressive and manic symptomatology). The current study examined sleep dysfunction in adolescents at ultra high-risk (UHR) for psychosis, relationships between sleep disturbances and psychosis symptoms, volume of an integral sleep-structure (thalamus), and associations between thalamic abnormalities and sleep impairment in UHR youth.
Method
Thirty-three UHR youth and 33 healthy controls (HC) participated in a self-assessment of sleep functioning (Pittsburgh Sleep Quality Index; PSQI), self and parent-report clinical interviews, and structural magnetic resonance imaging (MRI).
Results
UHR adolescents displayed increased latency to sleep onset and greater sleep disturbances/disrupted continuity compared to HC youth, over and above concurrent mood symptoms. Among UHR youth, increased sleep dysfunction was associated with greater negative symptom severity but not positive symptoms. Compared to HC adolescents, UHR participants displayed decreased bilateral thalamus volume, which was associated with increased sleep dysfunction.
Conclusions
Sleep dysfunction occurs during the pre-psychotic period, and may play a role in the etiology and pathophysiology of psychosis. In addition, the relationship of disrupted sleep to psychosis symptoms in UHR youth indicates that prevention and intervention strategies may be improved by targeting sleep stabilization in the pre-psychotic period.
doi:10.1016/j.schres.2013.09.015
PMCID: PMC3855888  PMID: 24094679
Schizophrenia; Premorbid; Psychosis; Ultra High-Risk; Prodromal; Sleep Dysfunction
6.  Tracking the Sleep Onset Process: An Empirical Model of Behavioral and Physiological Dynamics 
PLoS Computational Biology  2014;10(10):e1003866.
The sleep onset process (SOP) is a dynamic process correlated with a multitude of behavioral and physiological markers. A principled analysis of the SOP can serve as a foundation for answering questions of fundamental importance in basic neuroscience and sleep medicine. Unfortunately, current methods for analyzing the SOP fail to account for the overwhelming evidence that the wake/sleep transition is governed by continuous, dynamic physiological processes. Instead, current practices coarsely discretize sleep both in terms of state, where it is viewed as a binary (wake or sleep) process, and in time, where it is viewed as a single time point derived from subjectively scored stages in 30-second epochs, effectively eliminating SOP dynamics from the analysis. These methods also fail to integrate information from both behavioral and physiological data. It is thus imperative to resolve the mismatch between the physiological evidence and analysis methodologies. In this paper, we develop a statistically and physiologically principled dynamic framework and empirical SOP model, combining simultaneously-recorded physiological measurements with behavioral data from a novel breathing task requiring no arousing external sensory stimuli. We fit the model using data from healthy subjects, and estimate the instantaneous probability that a subject is awake during the SOP. The model successfully tracked physiological and behavioral dynamics for individual nights, and significantly outperformed the instantaneous transition models implicit in clinical definitions of sleep onset. Our framework also provides a principled means for cross-subject data alignment as a function of wake probability, allowing us to characterize and compare SOP dynamics across different populations. This analysis enabled us to quantitatively compare the EEG of subjects showing reduced alpha power with the remaining subjects at identical response probabilities. Thus, by incorporating both physiological and behavioral dynamics into our model framework, the dynamics of our analyses can finally match those observed during the SOP.
Author Summary
How can we tell when someone has fallen asleep? Understanding the way we fall asleep is an important problem in sleep medicine, since sleep disorders can disrupt the process of falling asleep. In the case of insomnia, subjects may fall asleep too slowly, whereas during sleep deprivation or narcolepsy, subjects fall asleep too quickly. Current methods for tracking the wake/sleep transition are time-consuming, subjective, and simplify the sleep onset process in a way that severely limits the accuracy, power, and scope of any resulting clinical metrics. In this paper, we describe a new physiologically principled method that dynamically combines information from brainwaves, muscle activity, and a novel minimally-disruptive behavioral task, to automatically create a continuous dynamic characterization of a person's state of wakefulness. We apply this method to a cohort of healthy subjects, successfully tracking the changes in wakefulness as the subjects fall asleep. This analysis reveals and statistically quantifies a subset of subjects who still respond to behavioral stimuli even though their brain would appear to be asleep by clinical measures. By developing an automated tool to precisely track the wake/sleep transition, we can better characterize and diagnose sleep disorders, and more precisely measure the effect of sleep medications.
doi:10.1371/journal.pcbi.1003866
PMCID: PMC4183428  PMID: 25275376
7.  Insomnia is a frequent finding in adults with Asperger syndrome 
BMC Psychiatry  2003;3:12.
Background
Asperger syndrome (AS) is a neurodevelopmental disorder belonging to autism spectrum disorders with prevalence rate of 0,35% in school-age children. It has been most extensively studied in childhood while there is scarcity of reports concerning adulthood of AS subjects despite the lifelong nature of this syndrome. In children with Asperger syndrome the initiation and continuity of sleep is disturbed because of the neuropsychiatric deficits inherent of AS. It is probable that sleep difficulties are present in adulthood as well. Our hypothesis was that adults with AS suffer from difficulty in initiating and maintaining sleep and nonrestorative sleep (insomnia).
Methods
20 AS without medication were compared with 10 healthy controls devoid of neuropsychiatric anamnesis. Clinical examination, blood test battery and head MRI excluded confounding somatic illnesses. Structured psychiatric interview for axis-I and axis-II disorders were given to both groups as well as Beck Depression Inventory and Wechsler adult intelligence scale, revised version.
Sleep quality was assessed with sleep questionnaire, sleep diary during 6 consecutive days and description of possible sleep problems by the participants own words was requested.
Results
compared with controls and with normative values of good sleep, AS adults had frequent insomnia. In sleep questionnaire 90% (18/20), in sleep diary 75% (15/20) and in free description 85% (17/20) displayed insomnia. There was a substantial psychiatric comorbidity with only 4 AS subject devoid of other axis-I or axis-II disorders besides AS. Also these persons displayed insomnia. It can be noted that the distribution of psychiatric diagnoses in AS subjects was virtually similar to that found among patient with chronic insomnia.
Conclusions
the neuropsychiatric deficits inherent of AS predispose both to insomnia and to anxiety and mood disorders. Therefore a careful assessment of sleep quality should be an integral part of the treatment plan in these individuals. Conversely, when assessing adults with chronic insomnia the possibility of autism spectrum disorders as one of the potential causes of this condition should be kept in mind.
doi:10.1186/1471-244X-3-12
PMCID: PMC270035  PMID: 14563215
Asperger; sleep; insomnia
8.  The association of gout with sleep disorders: a cross-sectional study in primary care 
Background
Both gout and sleep apnoea are associated with the metabolic syndrome. Hyperuricaemia is also prevalent in sleep apnoea syndrome. The objective of this study was to examine the association between gout and sleep apnoea and other sleep disorders.
Methods
Data were taken from a validated database of general practice records from nine practices in the UK between 2001 and 2008. People consulting for gout were identified via Read codes and each matched with four controls for age, gender, practice and year of gout consultation. Sleep problems and confounding comorbidities were also identified via Read codes. Medications were identified through a linked database of prescription records. The association between gout and sleep disorders was assessed using a logistic regression model, adjusting for ischaemic heart disease, hypertension, diabetes mellitus and diuretic use.
Results
1689 individuals with gout were identified and each successfully matched to four controls. Amongst those with gout, the prevalence of any sleep problem was 4.9%, sleep problems other than sleep apnoea 4.2%, and sleep apnoea 0.7%, compared to 3.5%, 3.2% and 0.3% respectively in controls. Gout was associated with any sleep problem (odds ratio (OR) 1.44; 95% confidence interval (CI) 1.11, 1.87), sleep problems other than sleep apnoea (OR 1.36; 95% CI 1.03, 1.80), and sleep apnoea (OR 2.10; 95% CI 1.01, 4.39). On multivariable analysis, gout remained significantly associated with any sleep problem (OR 1.39; 95% CI 1.06, 1.81) and sleep problems other than sleep apnoea (OR 1.37; 95% CI 1.03, 1.82), however the association with sleep apnoea was attenuated (OR 1.48, 95% CI 0.70, 3.14).
Conclusions
Gout and sleep problems appear to be associated and clinicians should be aware of the co-existence of these two conditions. Larger prospective epidemiological studies are required to explore causality.
doi:10.1186/1471-2474-14-119
PMCID: PMC3621781  PMID: 23557073
Gout; Sleep; Apnea; General practice; Metabolic syndrome X
9.  Sleep disorders in children 
Clinical Evidence  2007;2007:2304.
Introduction
Sleep disorders may affect 20-30% of young children, and include excessive daytime sleepiness, problems getting to sleep (dysomnias), or undesirable phenomena during sleep (parasomnias), such as sleep terrors, and sleepwalking. Children with physical or learning disabilities are at increased risk of sleep disorders.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of treatments for dysomnias in children? What are the effects of treatments for parasomnias in children? We searched: Medline, Embase, The Cochrane Library and other important databases up to September 2006 (BMJ Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 14 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review we present information relating to the effectiveness and safety of the following interventions: antihistamines, behavioural therapy plus benzodiazepines, or plus chloral and derivates, exercise, extinction and graduated extinction, light therapy, melatonin, safety/protective interventions for parasomnias, scheduled waking (for parasomnias), sleep hygiene, and sleep restriction.
Key Points
Sleep disorders may affect 20-30% of young children, and include excessive daytime sleepiness, problems getting to sleep (dysomnias), or undesirable phenomena during sleep (parasomnias), such as sleep terrors, and sleepwalking. Children with physical or learning disabilities are at increased risk of sleep disorders. Other risk factors include the child being the first born, having a difficult temperament or having had colic, and increased maternal responsiveness.
There is a paucity of evidence about effective treatments for sleep disorders in children, especially parasomnias, but behavioural interventions may be the best first-line approach.
Extinction and graduated extinction interventions improve settling and reduce night wakes compared with placebo in healthy children, and in children with learning disabilities. Graduated extinction may be less distressing for parents, and therefore may have better compliance.Sleep hygiene interventions may reduce bedtime tantrums in healthy children compared with placebo, with similar effectiveness to graduated extinction.Sleep hygiene plus graduated extinction may reduce bedtime tantrums in children with physical or learning disabilities.We don't know whether combining behavioural therapy with benzodiazepines or with chloral improves sleep or parasomnias.
Melatonin may improve sleep onset and sleep time compared with placebo in healthy children, but we don't know if it is beneficial in children with disabilities, if it improves parasomnias, or what its long-term effects might be. We don't know whether antihistamines, exercise, light therapy, or sleep restriction improve dysomnias or parasomnias in children.We don't know whether safety or protective interventions, scheduled waking, extinction, or sleep hygiene are effective in children with parasomnias.
PMCID: PMC2943792  PMID: 19450298
10.  Study of Sleep Habits and Sleep Problems Among Medical Students of Pravara Institute of Medical Sciences Loni, Western Maharashtra, India 
Background:
Good quality sleep and adequate amount of sleep are important in order to have better cognitive performance and avoid health problems and psychiatric disorders.
Aim:
The aim of this study was to describe sleep habits and sleep problems in a population of undergraduates, interns and postgraduate students of Pravara Institute of Medical Sciences (Deemed University), Loni, Maharashtra, India.
Subject and Methods:
Sleep habits and problems were investigated using a convenience sample of students from Pravara Institute of Medical Sciences (Deemed University), Loni, Maharashtra, India. The study was carried out during Oct. to Dec. 2011 with population consisted of total 150 medical students. A self-administered questionnaire developed based on Epworth Daytime Sleepiness Scale and Pittsburgh Sleep Quality Index was used. Data was analyzed by using Statistical Package of Social Sciences (SPSS) version 16.0.
Results:
In this study, out of 150 medical students, 26/150 (17.3%) students had abnormal levels of daytime sleepiness while 20/150 (13.3%) were border line. Sleep quality in females was better than the male.
Conclusion:
Disorders related to poor sleep qualities are significant problems among medical students in our institution. Caffeine and alcohol ingestion affected sleep and there was high level of daytime sleepiness. Sleep difficulties resulted in irritability and affected lifestyle and interpersonal relationships.
doi:10.4103/2141-9248.109488
PMCID: PMC3634224  PMID: 23634330
Medical students; Sleep disorders; Sleep habits; Sleep quality
11.  An assessment of quality of sleep and the use of drugs with sedating properties in hospitalized adult patients 
Background
Hospitalization can significantly disrupt sleeping patterns. In consideration of the previous reports of insomnia and apparent widespread use of benzodiazepines and other hypnotics in hospitalized patients, we conducted a study to assess quality of sleep and hypnotic drug use in our acute care adult patient population. The primary objectives of this study were to assess sleep disturbance and its determinants including the use of drugs with sedating properties.
Methods
This single-centre prospective study involved an assessment of sleep quality for consenting patients admitted to the general medicine and family practice units of an acute care Canadian hospital. A validated Verran and Snyder-Halpern (VSH) Sleep Scale measuring sleep disturbance, sleep effectiveness, and sleep supplementation was completed daily by patients and scores were compared to population statistics. Patients were also asked to identify factors influencing sleep while in hospital, and sedating drug use prior to and during hospitalization was also assessed.
Results
During the 70-day study period, 100 patients completed at least one sleep questionnaire. There was a relatively even distribution of males versus females, most patients were in their 8th decade of life, retired, and suffered from multiple chronic diseases. The median self-reported pre-admission sleep duration for participants was 8 hours and our review of PharmaNetR profiles revealed that 35 (35%) patients had received a dispensed prescription for a hypnotic or antidepressant drug in the 3-month period prior to admission. Benzodiazepines were the most common sedating drugs prescribed. Over 300 sleep disturbance, effective and supplementation scores were completed. Sleep disturbance scores across all study days ranged 16–681, sleep effectiveness scores ranged 54–402, while sleep supplementation scores ranged between 0–358. Patients tended to have worse sleep scores as compared to healthy non-hospitalized US adults in all three scales. When compared to US non-hospitalized adults with insomnia, our patients demonstrated sleep disturbance and supplementation scores that were similar on Day 1, but lower (i.e. improved) on Day 3, while sleep effectiveness were higher (i.e. better) on both days. There was an association between sleep disturbance scores and the number of chronic diseases, the presence of pain, the use of bedtime tricyclic antidepressants, and the number of chronic diseases without pain. There was also an association between sleep effectiveness scores and the length of hospitalization, the in hospital use of bedtime sedatives and the presence of pain. Finally, an association was identified between sleep supplementation scores and the in hospital use of bedtime sedatives (tricyclic antidepressants and loxapine), and age. Twenty-nine (29%) patients received a prescription for a hypnotic drug while in hospital, with no evidence of pre-admission hypnotic use. The majority of these patients were prescribed zopiclone, lorazepam or another benzodiazepine.
Conclusions
The results of this study reveal that quality of sleep is a problem that affects hospitalized adult medical service patients and a relatively high percentage of these patients are being prescribed a hypnotic prior to and during hospitalization.
doi:10.1186/1477-7525-2-17
PMCID: PMC521202  PMID: 15040803
12.  Beyond fatigue: Assessing variables associated with sleep problems and use of sleep medications in multiple sclerosis 
Clinical Epidemiology  2010;2:99-106.
Background:
Recent research indicates that sleep disturbances are common in persons with multiple sclerosis (MS), though research to date has primarily focused on the relationship between fatigue and sleep. In order to improve treatment of sleep disorders in MS, a better understanding of other factors that contribute to MS sleep disturbance and use of sleep medications in this population is needed.
Methods:
Individuals with MS (N = 473) involved in an ongoing self-report survey study were asked to report on use of over-the-counter and prescription sleep medications. Participants completed the Medical Outcomes Study Sleep (MOSS) scale and other common self-report symptom measures. Multiple regression was used to evaluate factors associated with sleep problems and descriptive statistics were generated to examine use of sleep medications.
Results:
The mean score on the MOSS scale was 35.9 (standard deviation, 20.2) and 46.8% of the sample had moderate or severe sleep problems. The majority of participants did not use over-the-counter (78%) or prescription (70%) sleep medications. In a regression model variables statistically significantly associated with sleep problems included depression, nighttime leg cramps, younger age, pain, female sex, fatigue, shorter duration of MS, and nocturia. The model explained 45% of the variance in sleep problems. Of the variance explained, depression accounted for the majority of variance in sleep problems (33%), with other variables explaining significantly less variance.
Conclusions:
Regression results indicate that fatigue may play a minor role in sleep disturbance in MS and that clinicians should consider the interrelationship between depression and sleep problems when treating either symptom in this population. More research is needed to explore the possibility of under-treatment of sleep disorders in MS and examine the potential effectiveness of nonpharmaceutical treatment options.
PMCID: PMC2936768  PMID: 20838467
multiple sclerosis; sleep; depression; fatigue; nonpharmaceutical treatments; self-medication
13.  Beyond fatigue: Assessing variables associated with sleep problems and use of sleep medications in multiple sclerosis 
Clinical epidemiology  2010;2010(2):99-106.
Background
Recent research indicates that sleep disturbances are common in persons with multiple sclerosis (MS), though research to date has primarily focused on the relationship between fatigue and sleep. In order to improve treatment of sleep disorders in MS, a better understanding of other factors that contribute to MS sleep disturbance and use of sleep medications in this population is needed.
Methods
Individuals with MS (N = 473) involved in an ongoing self-report survey study were asked to report on use of over-the-counter and prescription sleep medications. Participants completed the Medical Outcomes Study Sleep (MOSS) scale and other common self-report symptom measures. Multiple regression was used to evaluate factors associated with sleep problems and descriptive statistics were generated to examine use of sleep medications.
Results
The mean score on the MOSS scale was 35.9 (standard deviation, 20.2) and 46.8% of the sample had moderate or severe sleep problems. The majority of participants did not use over-the-counter (78%) or prescription (70%) sleep medications. In a regression model variables statistically significantly associated with sleep problems included depression, nighttime leg cramps, younger age, pain, female sex, fatigue, shorter duration of MS, and nocturia. The model explained 45% of the variance in sleep problems. Of the variance explained, depression accounted for the majority of variance in sleep problems (33%), with other variables explaining significantly less variance.
Conclusions
Regression results indicate that fatigue may play a minor role in sleep disturbance in MS and that clinicians should consider the interrelationship between depression and sleep problems when treating either symptom in this population. More research is needed to explore the possibility of under-treatment of sleep disorders in MS and examine the potential effectiveness of nonpharmaceutical treatment options.
doi:10.2147/CLEP.S10425
PMCID: PMC2936768  PMID: 20838467
multiple sclerosis; sleep; depression; fatigue; nonpharmaceutical treatments; self-medication
14.  Are sleep problems under-recognised in general practice? 
Archives of Disease in Childhood  2004;89(8):708-712.
Aims: To evaluate the frequency of sleep problems in Australian children aged 4.5–16.5 years, and to determine whether the frequency of sleep problems on questionnaire predicts the reporting of sleep problems at consultation.
Methods: Parents of 361 children (aged 4.5–16.5 years) attending their general practitioner for "sick" visits were asked to assess their child's sleep over the previous six months using the Sleep Disturbance Scale for Children, from which six sleep "disorder" factors and a total sleep problem score were obtained.
Results: The percentage of children with a total sleep problem score indicative of clinical significance (T score >70 or >95th centile) was 24.6% (89/361). Despite this high frequency, parents only addressed sleep problems in 4.1% (13/317) of cases and reported that GPs discussed sleep problems in 7.9% (25/317) of cases. Of the 79 children who reported total sleep problem T scores in the clinical range, only 13.9% (11/79) discussed sleep with their general practitioner within the previous 12 months. Regression analyses revealed an age related decrease in problems with sleep-wake transition and sleep related obstructive breathing; sleep hyperhydrosis, initiating and maintaining sleep, and excessive daytime sleepiness did not significantly decrease with age. No significant gender differences were observed.
Conclusions: Results suggest that chronic sleep problems in Australian children are significantly under-reported by parents during general practice consultations despite a relatively high frequency across all age groups. Given the impact on children and families, there is a need for increased awareness of children's sleep problems in the community and for these to be more actively addressed at consultation.
doi:10.1136/adc.2003.027011
PMCID: PMC1720041  PMID: 15269066
15.  Factors Associated with Sleep Disturbance in Women of Mexican Descent 
Journal of advanced nursing  2012;68(10):2256-2266.
Aims
The aims were to identify the most useful parameters of acculturation in relation to self reported sleep disturbance and describe risk factors for sleep disturbance in women of Mexican descent.
Background
Little is known about acculturation as a factor for poor sleep in the context of other personal factors such as income or sense of resilience or mastery for Latinas in the United States.
Methods
These personal factors were incorporated into a modification of the Conceptual Framework of Impaired Sleep to guide our secondary analysis of self-reported sleep disturbance. Cross sectional data from a convenience sample of 312 women of Mexican descent of childbearing age (21-40 years) located in an urban California community were collected and previously analyzed in relation to depressive symptoms and post traumatic stress disorder. The General Sleep Disturbance Scale (in English and Spanish) was used to assess sleep disturbance.
Results
Early socialization to the United States during childhood was the most useful acculturation parameter for understanding self reported sleep disturbance in this sample. In a multivariate regression analysis, three factors (higher acculturation, lower income, and higher depressive symptoms) were significant in accounting for 40% of the variance in sleep disturbance.
Conclusion
When low income Latinas of Mexican descent report sleep problems, clinicians should probe for environmental sleep factors associated with low income, such as noise, over-crowding, and exposure to trauma and violence, and refer the woman to psychotherapy and counselling rather than merely prescribe a sleep medication.
doi:10.1111/j.1365-2648.2011.05918.x
PMCID: PMC3962190  PMID: 22221152
16.  Polysomnographic sleep patterns of non-depressed, non-medicated children with generalized anxiety disorder 
Journal of affective disorders  2012;147(0):379-384.
Background
Polysomnographic (PSG) studies of children with psychiatric illness have primarily focused on depressed samples. Children with generalized anxiety disorder (GAD) report high rates of sleep problems yet investigation of objective sleep patterns in non-depressed children with GAD are unavailable. Identification of unique clinical features linking early GAD with sleep disturbance, including possible HPA activation during the pre-sleep period, is needed to inform understanding of effective treatments.
Method
Thirty non-medicated, pre-pubescent children (ages 7–11 years) were assessed including 15 children with GAD and 15 matched healthy controls. Anxious children had GAD as their primary diagnosis and did not meet criteria for secondary mood disorders. All participants underwent structured diagnostic assessment and laboratory-based polysomnography (PSG). State anxiety and salivary cortisol were assessed prior to light out on the PSG night.
Results
Children with GAD showed significantly increased sleep onset latency and reduced latency to rapid eye movement (REM) sleep compared to controls. Marginal differences in form of reduced sleep efficiency and increased total REM sleep also were found in the GAD group. Pre-sleep anxiety and cortisol levels did not differ between the two groups.
Limitations
A small sample size, time-limited assessment of cortisol, and possible first night effects should be considered.
Conclusions
Results of this study provide initial evidence of PSG-based differences in children with GAD compared to controls. Follow-up studies are needed to explore the course of sleep alterations and whether targeting sleep problems early in the course of GAD might improve clinical outcomes.
doi:10.1016/j.jad.2012.08.015
PMCID: PMC3985749  PMID: 23026127
Generalized Anxiety Disorder; Children; Depression; Sleep; Polysomnography; Cortisol
17.  Snoring and breathing pauses during sleep: telephone interview survey of a United Kingdom population sample. 
BMJ : British Medical Journal  1997;314(7084):860-863.
OBJECTIVES: To determine the prevalence of snoring, breathing pauses during sleep, and obstructive sleep apnoea syndrome and determine the relation between these events and sociodemographic variables, other health problems, driving accidents, and consumption of healthcare resources. DESIGN: Telephone interview survey directed by a previously validated computerised system (Sleep-Eval). SETTING: United Kingdom. SUBJECTS: 2894 women and 2078 men aged 15-100 years who formed a representative sample of the non-institutionalised population. MAIN OUTCOME MEASURES: Interview responses. RESULTS: Forty per cent of the population reported snoring regularly and 3.8% reported breathing pauses during sleep. Regular snoring was significantly associated with male sex, age 25 or more, obesity, daytime sleepiness or naps, night time awakenings, consuming large amounts of caffeine, and smoking. Breathing pauses during sleep were significantly associated with obstructive airways or thyroid disease, male sex, age 35-44 years, consumption of anxiety reducing drugs, complaints of non-restorative sleep, and consultation with a doctor in the past year. The two breathing symptoms were also significantly associated with drowsiness while driving. Based on minimal criteria of the International classification of Sleep Disorders (1990), 1.9% of the sample had obstructive sleep apnoea syndrome. In the 35-64 year age group 1.5% of women (95% confidence interval 0.8% to 2.2%) and 3.5% of men (2.4% to 4.6%) had obstructive sleep apnoea syndrome. CONCLUSIONS: Disordered breathing during sleep is widely underdiagnosed in the United Kingdom. The condition is linked to increased use of medical resources and a greater risk of daytime sleepiness, which augments the risk of accidents. Doctors should ask patients and bed partners regularly about snoring and breathing pauses during sleep.
PMCID: PMC2126255  PMID: 9093095
18.  An investigation on sleep behaviors of the elderly hospitalized in Zahedan 
Background:
Sleep is an essential need in every individual's life. A disorder in the natural sleep can cause physical and mental problems. The elderly are usually faced with more sleep problems. Therefore, the present study aimed to define sleep behavior among the elderly hospitalized in Zahedan.
Materials and Methods:
This is a descriptive analytical study conducted on 300 elderly people aged 60 years and over who were hospitalized in Zahedan. In this research convenience sampling method was used and the research tool was a questionnaire. The data were collected through interviews. Descriptive (frequency distribution) and inferential (X2) statistical tests were employed to analyze the data.
Findings:
The results showed that 62% of the hospitalized elderly people (total of 300) had sleep disorder. About 44.7%took sleep medication in order to sleep, and only 16.7% did not take sleeping medications. About 44.7% had no special schedule for the time of their sleeping and waking up, and 4.3% were involved in drug abuse and smoking, and had a big dinner before sleeping. There was a significant association between sleep disorder, gender, education, living in urban or rural areas, the cause of hospitalization, and suffering from a chronic disease
Conclusions:
Sleep disorder and inappropriate sleep related behaviors had a high prevalence among the elderly. With regard to the important role of sleep in the quality of life of the elderly, detection of the reasons of sleep disorder, motivating them to practice an appropriate sleep behavior, and preventing them from having inappropriate sleep related behaviors are crucial issues.
PMCID: PMC3590697  PMID: 23493461
Sleep behavior; elderly; hospitalized elderly
19.  Sleep and Sleep Disorders in Rare Hereditary Diseases: A Reminder for the Pediatrician, Pediatric and Adult Neurologist, General Practitioner, and Sleep Specialist 
Although sleep abnormalities in general and sleep-related breathing disorders (SBD) in particular are quite common in healthy children; their presence is notably under-recognized. Impaired sleep is a frequent problem in subjects with inborn errors of metabolism as well as in a variety of genetic disorders; however, they are commonly either missed or underestimated. Moreover, the complex clinical presentation and the frequently life-threatening symptoms are so overwhelming that sleep and its quality may be easily dismissed. Even centers, which specialize in rare genetic-metabolic disorders, are expected to see only few patients with a particular syndrome, a fact that significantly contributes to the under-diagnosis and treatment of impaired sleep in this particular population. Many of those patients suffer from reduced life quality associated with a variable degree of cognitive impairment, which may be worsened by poor sleep and abnormal ventilation during sleep, abnormalities which can be alleviated by proper treatment. Even when such problems are detected, there is a paucity of publications on sleep and breathing characteristics of such patients that the treating physician can refer to. In the present paper, we provide an overview of sleep and breathing characteristics in a number of rare genetic–metabolic disorders with the hope that it will serve as a reminder for the medical professional to look for possible impaired sleep and SBD in their patients and when present to apply the appropriate evaluation and treatment options.
doi:10.3389/fneur.2014.00133
PMCID: PMC4101612  PMID: 25101051
sleep apnea; breathing; genetic; metabolic; neuromuscular; upper airway
20.  Identifying Adolescent Sleep Problems 
PLoS ONE  2013;8(9):e75301.
Objectives
To examine the efficacy of self-report and parental report of adolescent sleep problems and compare these findings to the incidence of adolescents who fulfill clinical criteria for a sleep problem. Sleep and daytime functioning factors that predict adolescents’ self-identification of a sleep problem will also be examined.
Method
308 adolescents (aged 13–17 years) from eight socioeconomically diverse South Australian high schools participated in this study. Participants completed a survey battery during class time, followed by a 7-day Sleep Diary and the Flinders Fatigue Scale completed on the final day of the study. Parents completed a Sleep, Medical, Education and Family History Survey.
Results
The percentage of adolescents fulfilling one or more of the criteria for a sleep problem was inordinately high at 66%. Adolescent self-reporting a sleep problem was significantly lower than the adolescents who had one or more of the clinical criteria for a sleep problem (23.1% vs. 66.6%; χ2 = 17.46, p<.001). Parental report of their adolescent having a sleep problem was significantly lower than adolescent self-report (14.3% vs. 21.1%, p<.001). Adolescents who reported unrefreshing sleep were 4.81 times more likely to report a sleep problem. For every hour that bedtime was delayed, the odds of self-reporting a sleep problem increased by 1.91 times, while each additional 10 minutes taken to fall asleep increased the odds 1.40 times.
Conclusion
While many adolescents were found to have sleep patterns indicative of a sleep problem, only a third of this number self-identify having a sleep problem, while only a sixth of this number are indicated by parental report. This study highlights important features to target in future sleep education and intervention strategies for both adolescents and parents.
doi:10.1371/journal.pone.0075301
PMCID: PMC3782469  PMID: 24086501
21.  Sleep Quality in Parkinson’s Disease: An Examination of Clinical Variables 
The etiology of sleep problems in PD is not well understood, as they may arise from the pathology of the disease or from other disease related-factors such as motor dysfunction, dopaminergic medication, and mood disturbances. The aim of this study was to investigate factors associated with sleep including disease-related variables such as motor symptom severity, dose of medication and mood and disease subtypes. Thirty-five non-demented patients with PD were included. Sleep was measured using 24-hour wrist actigraphy over a seven-day period, during which time participants kept a sleep diary. Subjective sleep and arousal questionnaires included the Parkinson’s Disease Sleep Scale and Epworth Sleepiness Scale. Motor symptom severity and dopaminergic medication were significantly related to measures of sleep quality. Gender differences in sleep were found, with men having worse sleep quality and more excessive daytime sleepiness than women. We also found that actigraphy may serve as a useful tool for identifying individuals with possible REM behavior disorder, a sleep disorder that has important implications in early detection of PD.
doi:10.1097/WNN.0b013e31821a4a95
PMCID: PMC3126883  PMID: 21537164
22.  Childhood Obstructive Sleep Apnea Associates with Neuropsychological Deficits and Neuronal Brain Injury 
PLoS Medicine  2006;3(8):e301.
Background
Childhood obstructive sleep apnea (OSA) is associated with neuropsychological deficits of memory, learning, and executive function. There is no evidence of neuronal brain injury in children with OSA. We hypothesized that childhood OSA is associated with neuropsychological performance dysfunction, and with neuronal metabolite alterations in the brain, indicative of neuronal injury in areas corresponding to neuropsychological function.
Methods and Findings
We conducted a cross-sectional study of 31 children (19 with OSA and 12 healthy controls, aged 6–16 y) group-matched by age, ethnicity, gender, and socioeconomic status. Participants underwent polysomnography and neuropsychological assessments. Proton magnetic resonance spectroscopic imaging was performed on a subset of children with OSA and on matched controls. Neuropsychological test scores and mean neuronal metabolite ratios of target brain areas were compared.
Relative to controls, children with severe OSA had significant deficits in IQ and executive functions (verbal working memory and verbal fluency). Children with OSA demonstrated decreases of the mean neuronal metabolite ratio N-acetyl aspartate/choline in the left hippocampus (controls: 1.29, standard deviation [SD] 0.21; OSA: 0.91, SD 0.05; p = 0.001) and right frontal cortex (controls: 2.2, SD 0.4; OSA: 1.6, SD 0.4; p = 0.03).
Conclusions
Childhood OSA is associated with deficits of IQ and executive function and also with possible neuronal injury in the hippocampus and frontal cortex. We speculate that untreated childhood OSA could permanently alter a developing child's cognitive potential.
Childhood obstructive sleep apnea is associated with deficits of IQ and executive function and also with possible neuronal injury in the hippocampus and frontal cortex.
Editors' Summary
Background.
Sleep is essential for health, and in children it is crucial to normal development. Symptomatic childhood sleep-disordered breathing (SDB) is the name for a range of conditions in which children have difficulties with breathing when they are asleep. The conditions range from simple snoring to the most severe condition, known as obstructive sleep apnea (OSA). Apnea means a temporary absence of breathing, and in OSA this is caused by a temporary but repeated blockage of the flow of air to the lungs. In children, OSA occurs for a number of reasons including enlarged tonsils, long-term allergy, and obesity. About two in every hundred children have OSA. The symptoms of OSA are loud snoring at night, disrupted, restless sleep, undue tiredness, and difficulties in concentration. The main test for it is a sleep study (polysomnography). If untreated, researchers believe that it may lead to a number of long-term problems with health and learning; children with disorders of sleep have been shown to have memory problems, lower general intelligence, and worse executive function (the ability to adapt to new situations), and may have behavioral problems similar to those of attention deficit hyperactivity disorder (ADHD).
Why Was This Study Done?
Adults with sleep apnea have been shown to have abnormalities of parts of their brain, specifically the frontal cortex, cerebellum, and hippocampus, but so far there are no data on whether there are similar changes in children. Children with sleep apnea may have cognitive deficits, but the research on this topic is limited.
What Did the Researchers Do and Find?
The researchers wanted to investigate the brains of children with OSA to see if there was any evidence of changes in the brain and if these changes were associated with any learning problems. They studied 31 children (19 with OSA and 12 healthy controls, aged 6–16 y). Participants underwent polysomnography and neuropsychological assessments, such as IQ tests and tests of their ability to perform tasks involving decision making. Some of the children also had specialized scans of their brains (known as proton magnetic resonance spectroscopic imaging) that can measure the levels of certain metabolites—substances that are produced as a result of brain activity. The researchers then compared the neuropsychological test scores with the levels of the metabolites. They found that relative to controls, children with severe OSA had lower IQ and ability to perform tasks involving decision making. Children with OSA also had changes in metabolites in the brain similar to those seen in diseases in which there is damage to brain cells.
What Do These Findings Mean?
It seems clear that OSA in children is associated with learning problems, and that these learning problems may in turn be associated with changes in brain metabolites. The changes in metabolites are not necessarily permanent—in other diseases where changes have been found they can be reversed with treatment. If these results are confirmed in other children with OSA, it will highlight the importance of treating children for OSA as soon as possible. In addition, the measurement of metabolites may be a way of measuring how well children are responding to treatment.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0030301.
MedlinePlus's encyclopedia has an entry on sleep apnea
The American Sleep Apnea Association has information about having a child investigated for sleep apnea
The National Sleep Foundation also provides information about sleep disorders
doi:10.1371/journal.pmed.0030301
PMCID: PMC1551912  PMID: 16933960
23.  Role of respiratory sleep disorders in the pathogenesis of nocturnal angina and arrhythmias. 
Postgraduate Medical Journal  1994;70(822):275-280.
This report documents how respiratory sleep disorders can adversely effect ischaemic heart disease. Three male patients (aged 60-67 years) with proven ischaemic heart disease are described. They illustrate a spectrum of nocturnal cardiac dysfunction, two with nocturnal angina and one with nocturnal arrhythmias. Full sleep studies were performed in a dedicated sleep laboratory on all patients, and one patient had 48 hours of continuous Holter monitoring. Two patients were found to have obstructive sleep apnoea with apnoea/hypopnoea indices of 57 and 36 per hour, respectively, the former with nocturnal arrhythmias and the latter with nocturnal angina. In both cases, nasal continuous positive airways pressure successfully treated the sleep apnoea, with an associated improvement in nocturnal arrhythmias and angina. The third patient who presented with nocturnal angina, did not demonstrate obstructive sleep apnoea (apnoea/hypopnoea index = 7.2) but had significant oxygen desaturation during rapid eye movement (REM) sleep. This patient responded to a combination of nocturnal oxygen and protriptyline, an agent known to suppress REM sleep, and had no further nocturnal angina. All patients were considered to be an optimum cardiac medication and successful symptom resolution only occurred with the addition of specific therapy aimed at their sleep-related respiratory problem. We conclude that all patients with nocturnal angina or arrhythmias should have respiratory sleep abnormalities considered in their assessment.
PMCID: PMC2397870  PMID: 8183772
24.  Circadian-Related Sleep Disorders and Sleep Medication Use in the New Zealand Blind Population: An Observational Prevalence Survey 
PLoS ONE  2011;6(7):e22073.
Study Objectives
To determine the prevalence of self-reported circadian-related sleep disorders, sleep medication and melatonin use in the New Zealand blind population.
Design
A telephone survey incorporating 62 questions on sleep habits and medication together with validated questionnaires on sleep quality, chronotype and seasonality.
Participants
Participants were grouped into: (i) 157 with reduced conscious perception of light (RLP); (ii) 156 visually impaired with no reduction in light perception (LP) matched for age, sex and socioeconomic status, and (iii) 156 matched fully-sighted controls (FS).
Sleep Habits and Disturbances
The incidence of sleep disorders, daytime somnolence, insomnia and sleep timing problems was significantly higher in RLP and LP compared to the FS controls (p<0.001). The RLP group had the highest incidence (55%) of sleep timing problems, and 26% showed drifting sleep patterns (vs. 4% FS). Odds ratios for unconventional sleep timing were 2.41 (RLP) and 1.63 (LP) compared to FS controls. For drifting sleep patterns, they were 7.3 (RLP) and 6.0 (LP).
Medication Use
Zopiclone was the most frequently prescribed sleep medication. Melatonin was used by only 4% in the RLP group and 2% in the LP group.
Conclusions
Extrapolations from the current study suggest that 3,000 blind and visually impaired New Zealanders may suffer from circadian-related sleep problems, and that of these, fewer than 15% have been prescribed melatonin. This may represent a therapeutic gap in the treatment of circadian-related sleep disorders in New Zealand, findings that may generalize to other countries.
doi:10.1371/journal.pone.0022073
PMCID: PMC3138759  PMID: 21789214
25.  Obstructive Sleep Apnea and Risk of Cardiovascular Events and All-Cause Mortality: A Decade-Long Historical Cohort Study 
PLoS Medicine  2014;11(2):e1001599.
Tetyana Kendzerska and colleagues explore the association between physiological measures of obstructive sleep apnea other than the apnea-hypopnea index and the risk of cardiovascular events.
Please see later in the article for the Editors' Summary
Background
Obstructive sleep apnea (OSA) has been reported to be a risk factor for cardiovascular (CV) disease. Although the apnea-hypopnea index (AHI) is the most commonly used measure of OSA, other less well studied OSA-related variables may be more pathophysiologically relevant and offer better prediction. The objective of this study was to evaluate the relationship between OSA-related variables and risk of CV events.
Methods and Findings
A historical cohort study was conducted using clinical database and health administrative data. Adults referred for suspected OSA who underwent diagnostic polysomnography at the sleep laboratory at St Michael's Hospital (Toronto, Canada) between 1994 and 2010 were followed through provincial health administrative data (Ontario, Canada) until May 2011 to examine the occurrence of a composite outcome (myocardial infarction, stroke, congestive heart failure, revascularization procedures, or death from any cause). Cox regression models were used to investigate the association between baseline OSA-related variables and composite outcome controlling for traditional risk factors. The results were expressed as hazard ratios (HRs) and 95% CIs; for continuous variables, HRs compare the 75th and 25th percentiles. Over a median follow-up of 68 months, 1,172 (11.5%) of 10,149 participants experienced our composite outcome. In a fully adjusted model, other than AHI OSA-related variables were significant independent predictors: time spent with oxygen saturation <90% (9 minutes versus 0; HR = 1.50, 95% CI 1.25–1.79), sleep time (4.9 versus 6.4 hours; HR = 1.20, 95% CI 1.12–1.27), awakenings (35 versus 18; HR = 1.06, 95% CI 1.02–1.10), periodic leg movements (13 versus 0/hour; HR = 1.05, 95% CI 1.03–1.07), heart rate (70 versus 56 beats per minute [bpm]; HR = 1.28, 95% CI 1.19–1.37), and daytime sleepiness (HR = 1.13, 95% CI 1.01–1.28).The main study limitation was lack of information about continuous positive airway pressure (CPAP) adherence.
Conclusion
OSA-related factors other than AHI were shown as important predictors of composite CV outcome and should be considered in future studies and clinical practice.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder, particularly among middle-aged and elderly people. It is characterized by apnea—a brief interruption in breathing that lasts at least 10 seconds—and hypopnea—a decrease of more than 50% in the amplitude of breathing that lasts at least 10 seconds or clear but smaller decrease in amplitude associated with either oxygen desaturation or an arousal. Patients with OSA experience numerous episodes of apnea and hypopnea during the night; severe OSA is defined as having 30 or more episodes per hour (an apnea-hypopnea index [AHI] of >30). These breathing interruptions occur when relaxation of the upper airway muscles decreases the airflow, which lowers the amount of oxygen in the blood. As a result, affected individuals frequently wake from deep sleep as they struggle to breathe. Symptoms of OSA include loud snoring and daytime sleepiness. Treatments include lifestyle changes such as losing weight (excess fat around the neck increases airway collapse) and smoking cessation. For severe OSA, doctors recommend continuous positive airway pressure (CPAP), in which a machine blows pressurized air through a face mask into the airway to keep it open.
Why Was This Study Done?
OSA can be life-threatening. Most directly, daytime sleepiness can cause accidents, but OSA is also associated with an increased risk of developing cardiovascular disease (CVD, disease that affects the heart and the circulation). To date, studies that have investigated the association between OSA and the risk of myocardial infarction (heart attack), congestive heart failure, stroke, and other CVDs have used the AHI to diagnose and categorize the severity of OSA. However, by focussing on AHI, clinicians and researchers may be missing opportunities to improve their ability to predict which patients are at the highest risk of CVD. In this historical cohort study, the researchers investigate the association between other OSA-related variables (for example, blood oxygen saturation and sleep fragmentation) and the risk of cardiovascular events and all-cause mortality (death). A historical cohort study examines the medical records of groups of individuals who have different characteristics at baseline for the subsequent occurrence of specific outcomes.
What Did the Researchers Do and Find?
The researchers used administrative data (including hospitalization records and physicians' claims for services supplied to patients) to follow up adults referred for suspected OSA who underwent diagnostic polysomnography (a sleep study) at a single Canadian hospital between 1994 and 2010. A database of the polysomnography results provided information on OSA-related variables for all the study participants. Over an average follow-up of about 6 years, 11.5% of the 10,149 participants were hospitalized for a myocardial infarction, stroke, or congestive heart failure, underwent a revascularization procedure (an intervention that restores the blood supply to an organ or tissue after CVD has blocked a blood vessel), or had died from any cause. After adjusting for multiple established risk factors for CVD such as smoking and age in Cox regression models (a statistical approach that examines associations between patient variables and outcomes), several OSA-related variables (but not AHI) were significant predictors of CVD. The strongest OSA-related predictor of cardiovascular events or all-cause mortality was total sleep time spent with oxygen saturation below 90%, which increased the risk of a cardiovascular event or death by 50%. Other statistically significant OSA-related predictors (predictors that were unlikely to be associated with the outcome through chance) of cardiovascular events or death included total sleep time, number of awakenings, frequency of periodic leg movements, heart rate, and daytime sleepiness.
What Do These Findings Mean?
These findings indicate that OSA-related factors other than AHI are important predictors of the composite outcome of a cardiovascular event or all-cause mortality. Indeed, although AHI was significantly associated with the researchers' composite outcome in an analysis that did not consider other established risk factors for CVD (“confounders”), the association became non-significant after controlling for potential confounders. The accuracy of these findings, which need to be confirmed in other settings, is likely to be limited by the lack of information available about the use of CPAP by study participants and by the lack of adjustment for some important confounders. Importantly, however, these findings suggest that OSA-related factors other than AHI should be considered as predictors of CVD in future studies and in clinical practice.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001599.
The US National Heart Lung and Blood Institute has information (including several videos) about obstructive sleep apnea (in English and Spanish), sleep studies, heart disease, and other cardiovascular diseases (some information in English and Spanish)
The UK National Health Service Choices website provides information (including personal stories) about sleep apnea and about cardiovascular disease
The not-for-profit American Sleep Apnea Association provides detailed information about sleep apnea for patients and health-care professionals, including personal stories about the condition
The MedlinePlus encyclopedia has pages on obstructive sleep apnea and on polysomnography; MedlinePlus provides links to further information and advice about obstructive sleep apnea, heart diseases, and vascular diseases (in English and Spanish)
doi:10.1371/journal.pmed.1001599
PMCID: PMC3913558  PMID: 24503600

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