Sleep problems predict cortisol reactivity to stress in urban adolescents
Introduction
Almost 70% of US adolescents do not receive sufficient sleep (8 or more hours per night) and only 8% report optimal sleep duration of 9 or more hours [12]. Both insufficient sleep and sleep problems contribute to cognitive problems and poor mental and physical health over time [35]. Since adequate sleep is necessary for optimal functioning of the HPA axis [42] and dysregulation of the HPA axis contributes to cognitive, emotional, and health problems [24], alteration of HPA axis activity has been proposed as a key mechanism through which sleep problems lead to negative outcomes [27]. The relationship between sleep and HPA axis activity has been studied in children and adults, but little is known about this link during adolescence when both sleep and the HPA axis undergo significant developmental changes related to puberty [10], [35].
Among prepubertal children and adults, insufficient sleep and sleep problems consistently predict elevated cortisol levels throughout the day [13], [19], [22], [27], [32], [38]. The only study conducted with adolescents found no effect of sleep restriction on morning and evening cortisol levels [43], but the study was limited by small sample sizes in each experimental condition (n = 12 to 17). Children with sleep problems and sleep deprived adults also had greater cortisol reactivity to stress [19], [27], [38], but lower stress reactivity was observed in adult women with lower objectively measured sleep quality [46] and in 10–12 year olds with more self-reported sleep–wake problems [8]. In the latter study, there was no link between sleep–wake problems and cortisol reactivity among adolescents (13–17 years old); however, the conclusions are limited by a small sample size (N = 31 across both age groups) and the use of parent reports of sleep problems. Parent reports of sleep problems have been validated for pre-adolescent children [3], but they tend to underestimate older children's sleep problems [33] and may be particularly inaccurate for adolescents who receive less parental supervision [1].
Given the paucity of research on sleep and HPA axis in adolescence, this study sought to examine the effects of sleep on HPA axis activity in this age group. Specifically, we examined two dimensions of sleep — sleep duration and sleep problems, from the perspectives of adolescents and their parents, as well as cortisol levels before and after social stress. Because urban African American adolescents are more likely to experience insufficient sleep [1], [26] and their functioning is more negatively affected by lower sleep quality [5], we focused on the understudied population of urban and mostly African American adolescents. We hypothesized that shorter sleep duration and more sleep problems will predict higher cortisol levels and reactivity to stress (i.e., a social evaluative threat). Finally, because cortisol reactivity to stress in urban, African American adolescents and young adults varies by gender [2], [11], we also examined gender differences in the effects of sleep on stress-related cortisol regulation and reactivity.
Section snippets
Participants and procedures
Participants were 84 adolescents (M age 13.36 years, SD = 0.95; 50% male; 95% African American, 4% Caucasian and 1% Hispanic) who took part in the Coping with Violence Study. The sample was socioeconomically heterogeneous, but comprised primarily low-income families; average annual family income was $20,000–$25,000 (range <$5000 to $70,000–$90,000) and average parental education was some college but no degree (see Table 1 for sample characteristics). The adolescents were recruited from four public
Results
Preliminary data analyses identified seven cortisol observations as outliers; these values were truncated to 3 SD above the mean. Overall, 11% of participants had some missing data, but only 1.62% of observations were missing, supporting the use of FIML to utilize all available data in the regression analyses. The adolescents were on average 13 years old, early- to mid-pubertal, and at the 74th percentile for BMI (Table 1). Descriptives for all sleep items (Table 2) indicated that the most
Discussion
This study examined relationships between sleep and HPA axis activity in adolescence, focusing on a vulnerable, yet understudied population of urban and mostly African American adolescents. The results revealed greater cortisol reactivity to social evaluative threat among adolescents who reported more sleep problems and longer sleep duration, and whose parents also reported longer sleep duration. Girls showed greater cortisol elevation in response to stress than boys, as well as stronger
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