The most interesting finding of this analysis is that 1 in 4 women in the United States is at high risk for the presence of OSAS. Self-reported symptoms, such as habitual snoring, daytime sleepiness, and observed apnea, insomnia symptoms, and leg movements, are common in women at high risk for sleep apnea. The risk in women increases with advanced age, the presence of obesity, irregularity of the menstrual cycle, and menopause. Pregnant women had a similar risk for OSAS as nonpregnant women, and, more importantly in those pregnant women with high risk for OSAS, the reporting of pregnancy complications was very high. Women at high risk for OSAS have greater morbidity than women at low risk. Although many of our results also have been reported in previous studies, this analysis may help understand the lower prevalence of females in sleep medicine clinics, illustrating the possible atypical presentation of sleep apnea in women, and may help the medical community to increase its awareness about the significance of diagnosing sleep apnea in women. According to our results, OSAS prevalence in women may have increased in the United States in recent years. This report may enhance the need for future epidemiological studies.
Underrecognition of female cases of OSAS could be explained by a different clinical presentation.6
Several studies have investigated the gender-related differences in clinical presentation in order to explain the gender discrepancy in OSAS prevalence between general population and clinic-based studies. Redline et al.,7
in a general population study, reported that snoring and witnessed apnea were 2–3-fold more common in males. In contrast, data from the Wisconsin Sleep Cohort Study10
and the Sleep Heart Health study18
showed that women with sleep apnea report snoring, breathing cessation, and sleepiness equally with men. Clinical population studies11,19
also did not find significant gender-related differences in loud snoring and observed stops of breathing as symptoms at any level of apnea severity. Thus, data from both clinical and population-based studies suggest that the prevalence of common presenting symptoms of OSAS are not different between men and women and, therefore, cannot explain the reported lower prevalence of OSAS in the female population.
Our data showed that habitual snoring is common among women (19% of the whole sample). In a recent analysis from the 2005 NSF Sleep in America Poll,20
it was reported that habitual snoring was found in 13% of women and 19% of men. Thus, we found a higher prevalence among women that was equal to that reported previously among men. We also found that reported sleepiness at least a few days a week was also very common among females (23.3%).The 2005 NSF Poll analysis showed a similarly high prevalence of sleepiness in the general population (26%). Witnessed apneas every night were reported by 2.3% of women, similar to the prevalence reported in the 2005 Poll analysis (2% of women). Thus, the common symptoms of sleep apnea are also common in the female population and become significantly more prevalent among those women at high risk for sleep apnea. Witnessed apnea episodes, however, are less frequently reported than snoring among women at high risk. In clinical population studies,11,21
it has been shown that women with OSAS are less likely than men to report observed apneas, especially in milder forms of sleep apnea syndrome.19
This may be explained by a possibly different attitude of males to the sleep problems of their female bed partners. In conclusion, our data suggest that women at high risk for sleep apnea report symptoms of OSAS commonly and not differently from men, as has been shown in previous population studies.
It has been estimated that the prevalence of insomnia in the general population is about 10%,22
and female gender has been regarded as a risk factor for insomnia-like symptoms. About half of OSAS patients may have insomnia-like symptoms.23
We found that sleep onset insomnia, frequent awakenings, and maintenance insomnia were very common in the female population and that women at risk for the presence of sleep apnea had a higher prevalence of insomnia symptoms. Several studies have found that insomnia is much more likely to be the presenting symptom in women than in men. Although Krakow et al.24
found no gender difference in the frequency of insomnia symptoms in patients with sleep disordered breathing (SDB), Ambrogetti et al.21
showed that women had a 2-fold frequency of sleep onset insomnia compared with men. Shepertycky et al.11
showed that 1–5 women with OSAS had insomnia as the presenting symptom. In the community sample of the Sleep Heart Health Study,18
women more frequently than men had difficulty in falling or staying asleep, early morning awakenings, and leg cramps. Similarly, we found a strong association of unpleasant leg feelings and body movements with the estimated high risk for OSAS. These findings indicate that although women with OSAS frequently report the common symptoms, they may also have an atypical clinical presentation. Referring physicians should be aware of these features of clinical presentation in women and avoid relying only on the classic clinical symptoms. Atypical symptoms may explain the lower prevalence of female cases in clinic-based population studies. OSAS may not be different among genders, but there maybe some differences in particular aspects of presentation.
Risk factors for OSAS in women
We found that 1 in 4 women is at high risk for the presence of OSAS using the Berlin Questionnaire. This value is slightly higher than was found in the 2005 Poll for U.S. adults (21%) using similar methods,20
indicating a possible increase in the risk in women over these years. In our sample, 4% of women had been told by their doctors that they have OSA. This percentage, although not controlled with laboratory findings, is higher than the report from the Wisconsin Sleep Cohort Study1
reported in 1993, in which 2% of women met the minimal criteria for OSAS (AHI (apnea hypopnea index) >5 events per hour associated with daytime sleepiness). It is possible that OSAS is more prevalent in women today than it was previously. This could be attributed to the increase in obesity and age in the U.S. population or the increased diagnosis of female cases in sleep clinics.
OSAS is strongly associated with level of obesity.25
We found that high risk for OSAS was more prevalent among obese women and that the RR increased proportionally to obesity. Several population studies have demonstrated that the relationship of obesity to SDB is similar between men and women,15,26,27
although some have reported this relationship to be stronger in men than in women, who may develop SDB at much higher levels of obesity.28
Our findings showed a higher than 2-fold increase in high risk for OSAS in overweight subjects in comparison with normal weight women (8.5% vs. 21%, p
0.01) and an almost linear relationship of obesity with high risk for OSAS, suggesting that obesity may be the major risk factor for OSAS in women.
The risk for significant SDB increases with age.25
It has been suggested that younger women are protected from developing sleep apnea by the action of the female hormones on upper airway function.29
Low levels of female sex hormones are associated with an increased probability for SDB in women who experience daytime sleepiness.30
Progesterone levels affect pharyngeal dilator muscle activity, and higher activity of the genioglossus has been observed during the luteal phase of the menstrual cycle.31
It has been reported that the majority of female OSAS patients are older than men and postmenopausal.32
In this report, we found that the risk for OSAS in women increases with age and that the RR for OSAS was almost 2-fold higher in postmenopausal women in comparison with perimenopausal women and those with normal menstrual cycle status. Menopause appears to be an important risk factor for OSAS.
Obesity seems to be more important than age in increasing the risk for OSAS, although in older women, its effect is smaller than in younger women. This finding may reflect the more important role of menopause in this age group (>50 years old). Younger women need to be more obese than older women in order to develop a high risk for OSAS.
Pregnancy may enhance the risk for sleep apnea by changes in the anatomy of the respiratory system, alterations in sleep architecture, and weight gain. On the other hand, increased levels of female hormones during pregnancy may protect women from developing SDB.33
Although it has been found that snoring increases during pregnancy,34
the true prevalence of OSAS in pregnancy is not known. We found that in pregnant women a similar proportion to that of the whole sample was at risk for OSAS. This indicates that the risk is not increased in pregnancy, perhaps because of protective mechanisms. Similarly, postpartum women and women with past pregnancies did not show greater prevalence of risk for OSAS in comparison to the whole sample of women. More interestingly, pregnant women who were found to be at risk for OSAS more frequently reported complications of pregnancy, such as preeclampsia, premature contractions, preterm labor, and gestational diabetes. This finding raises concerns about the role of SDB in adverse pregnancy outcomes. Although the true incidence of SDB-related preeclampsia remains to be determined, several reports have shown a relationship of snoring and SDB with this condition.35
Our findings support the hypothesis that although pregnant women may be protected from the development of SDB, existing SDB during pregnancy is associated with maternal complications.
Medical disorders and risk for OSAS in women
Women at high risk for SDB reported the occurrence of several medical disorders more frequently than did women at low risk. This has several clinical implications in the diagnosis and management of SDB. Several studies have shown that more women than men with OSAS have been diagnosed with depression in the initial presentation and that women are more likely to be treated for depression before the diagnosis of sleep apnea.11,36
This finding, along with the atypical symptoms observed in women, could partly explain the lower presentation of women in sleep clinics, as their physicians attribute their symptoms to other diagnoses.
Women with high risk for OSAS also more frequently reported arterial hypertension or heart disease than low-risk women, indicating a possible relationship of sleep apnea with increased cardiovascular morbidity.15
Women at risk reported a greater prevalence of diabetes and polycystic ovarian syndrome, a condition characterized by increased insulin resistance. Increased insulin resistance has been linked to the increased cardiovascular disease observed in SDB.37
However, higher morbidity rates among women at risk may be due to obesity rather than OSAS. The lack of comparison between groups matched for age and BMI does not allow us to exclude the confounding role of obesity.
Limitations of study
The major limitations of the study derive from its nature, as has been stated in the previous report of the NSF Poll.20
Data were collected from a telephone review and could be inaccurate. This could be more important in the calculation of BMI, as weight and height were self-reported. Ethnicity may play a significant role in the epidemiology of sleep apnea.25
Only 19% of participants described themselves as nonwhite, and this percentage is not representative of the U.S. population. Thus, the risk for sleep apnea may have been underestimated. It should be acknowledged that the Berlin Questionnaire determines high risk for OSAS depending on self-reported symptoms and obesity which are known predictors of OSAS. It would be more precise if symptoms were evaluated as predictors of SDB diagnosed by polysomnography. The use of a slightly different version of the Berlin Questionnaire may also have influenced the estimation of risk of OSAS. Finally, this analysis has a univariate nature when a multivariable analysis would better control for confounding factors.