Adolescence is characterized by normative biological, psychological, and social changes that impact sleep duration and sleep schedules. In non-clinical samples, adolescents typically obtain less than the 9.2 hours of sleep that is recommended.1–5
Lack of adequate sleep can lead to chronic patterns of sleep deprivation and attempts at “catch-up sleep,” leading to increased variability in sleep patterns. Such poor sleep may lead to negative social, psychological, and public health consequences 6
, including suicide and motor vehicle accidents7
, risk taking behaviors8
, increased pain, reports of poor overall health9,10
, and poor functioning at school11,12
and work. In addition to biological variables (e.g., circadian timing)13
and genetic factors14,15
, demographic and health-related variables may affect sleep duration and night to night variability. Identifying such associated variables would help to target interventions as well as provide directions for future research.
Factors impacting the variation of sleep duration among adolescent populations have not been well studied, though previous research with younger children underscores the need for further investigation. Minority ethnicity, socioeconomic status, and years of parental education have been shown to be associated with amount of sleep obtained in school age children. Generally, children of minority ethnicity and of lower socioeconomic status obtain less sleep and have more sleep problems than their counterparts. Spilsbury et al.16
showed that minority boys were more than 4.8 times more likely than non-minority children to have bedtimes of 11 pm or later. Fredriksen et al.5
found that adolescents who were more economically disadvantaged obtained less sleep. Roberts, Roberts, and Chen17
found the direction and magnitude of the effect of minority status on symptoms of insomnia depended on the ethnic group, with Chinese-American youths at lower risk and Mexican youths at higher risk for insomnia. African-American children have also been shown to have a higher prevalence of sleep disordered breathing than European Americans18
, which is partly mediated by neighborhood disadvantage19
. A related finding is that greater education has been associated with better sleep quality and with higher income in adults20
Gender has been shown to relate to amount of sleep, frequency of sleep disturbances, and circadian preferences, though the etiology of these effects are unknown. Results of various studies report contradictory findings about whether boys or girls obtain more sleep. For example, one study found that girls obtained less sleep than boys and reported greater sleep disturbances21
. Another study showed that boys woke up later than girls on weekdays and hypothesized that this was a result of girls having more lengthy morning grooming routines22
. Alternatively, at least one other study has found that boys obtain less sleep than girls16
. Finally, one study found that girls reported a longer ideal sleep duration and that there are gender-related circadian preferences for morningness and eveningness in adolescents23
. It is possible that inconsistencies in the results of existing studies may in fact reflect differences in the measurement of sleep time (e.g., parent report, self-report, sleep diary, actigraphy) or in the age of the participants in the study.
Previous studies also suggest that health-related variables such as asthma, obesity, and attention deficit hyperactivity disorder (ADHD) may be associated with sleep duration and sleep quality. Children with asthma may experience increased nocturnal awakenings due to poor control of asthma symptoms or because of unrecognized sleep disordered breathing24
. In studies with both children and adults, body mass index (BMI) has also been associated with complaints of sleep problems, sleepiness, and decreased sleep time25, 26
. Finally, several studies with children have found a relationship between the presence of ADHD and sleep problems27–29
Limitations of previous studies and contribution of current study
Previous research has demonstrated that decreases in sleep quantity, in part related to shifts to later bedtimes, occur with the onset of adolescence, which may be partly attributable to hormonally mediated changes in circadian rhythm13
. However, there have been relatively few studies of the impact of demographic and health-related variables on sleep time or variability in sleep duration. Moreover, the conclusions that can be drawn from existing studies have been affected by methodological limitations, such as imprecise measurement of sleep duration. Much previous research has primarily relied on single item self-report or parent report of average total sleep time (i.e., “how many hours do you/does your child usually sleep at night”) or bedtimes and wake times, which may not be adequate in terms of validity or reliability. Recent studies have also shown that self-reports of sleep duration and quality may be distorted in certain populations, including anxious adults with higher levels of cognitive and physiological arousal30
and adolescents with major depressive disorder31
The majority of prior studies have not used objective measures of sleep duration such as actigraphy or polysomnography (PSG). The use of actigraphy is a methodological strength, not only because of limitations related to adolescent and parent self-reported sleep time as described above, but also because this technique is less intrusive than PSG and, this may provide representative data over several days obtained in the adolescent’s usual sleeping environment.
Finally, adolescents are an understudied age group, yet adolescence is a time when health habits may begin to shape the emergence of health status in adulthood. Moreover, chronological age may not be the most sensitive variable for defining adolescence, as physiological changes in sleep are thought to relate to physiological changes in puberty3, 32
. Thus, pubertal status is thought to be a more sensitive marker of physiological changes associated with adolescence, and in the current study Tanner staging was used to determine pubertal status.
Aims and Hypotheses
The primary aim of this study was to determine the relationship between sleep duration and individual subject characteristics (age, Tanner stage, parent education and income, neighborhood distress, gender, ethnicity) and health-related variables that may influence sleep in adolescents (ADHD, asthma, BMI). Based on previous research investigating individual characteristics that relate to sleep duration and variability in sleep duration5, 16, 20
, specific hypotheses were made about such characteristics. It was hypothesized that both environmental and host factors would be associated with sleep patterns. Specifically, we hypothesized that minority ethnicity, less parent education, lower parent income, and the presence of neighborhood distress would correlate with less mean total sleep duration and higher night-to-night variability. Additionally, it was hypothesized that male gender, higher BMI, the presence of asthma, and the presence of ADHD would relate to lower average sleep duration and higher night-to-night variability in sleep duration.