Bedtimes and the Blues: Evidence in Support of Improving Adolescent Sleep parental set bedtimes as a protective factor against depression and suicidal SLEEP 2010;33:97-106.

IN THIS ISSUE OF SLEEP, GANGWISCH AND COLLEAGUES1 PRESENT A NOVEL QUASI-EXPERIMENTAL ANALYSIS THAT SUPPORTS A CAUSAL RELATIONSHIP between chronic partial sleep deprivation and depression among adolescents. The positive association between chronic shortened sleep duration and depression is widely observed in the scientific literature.2–5 Although longitudinal data show that regular short sleep duration temporally precedes depression,4 it is unclear whether it is a cause of depression, or a prodromal or comorbid symptom. In order to design interventions that reduce depression and suicidal ideation, we need to better understand the causal pathways through which they arise. 
 
In the absence of conducting an unrealistic and ethically questionable experimental study that repeatedly restricts teenagers' sleep for long enough to potentially induce depressive symptoms, establishing a causal link presents a creative challenge to the researcher. The authors rise to the challenge by using parentally set bedtimes as a quasi-experiment, thereby taking advantage of a large nationally representative longitudinal study, Add Health. The idea is that parentally set bedtime is exogenous—not determined by the adolescent (nor his/her depressive state)—and thus not at risk of having a reverse causal relationship in which depression causes the late nights and short sleep durations. If it were true that parents set their children's bedtimes based on their own parenting beliefs, and that such beliefs are unrelated to the depressive tendencies of an adolescent, then parental set bedtimes might act similarly to an experimental design in which parents are “randomly assigning” children to early and late bedtimes. Operating on this identifying assumption, the authors find that adolescents with bedtimes past midnight are 24% more likely to have depression and 20% more likely to have suicidal ideation compared to those with bedtimes earlier than 10PM after adjustment for confounding variables. Additional analyses show that the parentally set bedtime-depression relationship is attenuated by statistical adjustment of self-reports of sleep duration and perceptions of sleep sufficiency. These results suggest that the mediating pathway is indeed related to sleep duration and that sleep duration matters for mental health in teenagers. 
 
The results of the analyses should be interpreted with some caution, however, because the use of parentally set bedtime does not fully satisfy the characteristics of a perfect exogenous force: 
 
There is likely some endogeneity between how adolescents behave and how parents set their bedtimes: parents may set bedtimes based on natural tendencies of the adolescent. For example, if a defiant teenager refuses to go to bed before midnight, a parent may know that it is fruitless to set a bedtime before 10 PM. 
 
Parents who enforce early bedtimes are likely to be different than parents who set later bedtimes in ways that aren't adjusted for in the analyses. That is, parents who set earlier bedtimes for their children may also have different household habits that are more conducive to reduced depression. Gangwisch et al.1 partially address this concern by showing that adolescent perception of parent caring does not account for the reason why earlier bedtimes are associated with less depression. 
 
Finally, the presence of an early parentally set bedtime does not necessarily mean that it is enforced, nor that adolescents sleep more. To address these concerns, Gangwisch and colleagues present the remarkable finding that nearly 70% of adolescents report that they comply with their parent-determined bedtimes. It is less surprising, yet still important that the data show a strong relationship between earlier parentally set bedtimes and increased total sleep time. 
 
Despite the imperfect exogeneity of the parentally set bedtime measure, this work adds weight to the evidence that insufficient sleep may cause depression and suicidal ideation. 
 
The study offers additional implications for adolescent health. In particular, this work shows that parentally mandated bedtimes actually do have a strong association with adolescent bedtimes and sleep duration. Given that regular high-quality sleep has been shown to have a wide range of positive outcomes on children and adolescents health and well-being,6–8 as a result of this work, we can recommend parents continue to set bedtimes for their children through adolescence. 
 
Gangwisch et al.1 report that on average adolescents are sleeping 7 hours and 53 minutes, more than an hour less than the recommended 9 hours. Thus, earlier bedtimes may not be enough, as a range of other factors affect adolescent sleep duration. For example, computer use and television watching are known to both delay time in bed and affect sleep quality.9,10 Future studies should investigate whether the implementation of other household routines (e.g., limiting electronics after 9 PM, restricting caffeine intake, and incorporating exercise into daily routines) can cause improvements in sleep and subsequent changes in mental and physical health. 
 
There are a variety of community-level factors that can affect adolescent sleep. For example, school start time is associated with earlier wake times, and less total sleep time.9,11,12 Additional research into the relationship between adolescent sleep duration and depression should consider looking for variation in depression based on school start time, because school start time may serve as a better exogenous variable. Beyond school start time, adolescent schedules are driven by extracurricular activities, after-school employment, and social activities. Policy and community efforts aimed at improving adolescent sleep should be explored. 
 
Given a growing body of knowledge linking child and adolescent sleep to cognitive, behavioral, and health outcomes, this article raises a larger concern about sleep contributing social disparities in health.6,7,13 Starting early in life, social, economic, and neighborhood factors have an influence on sleep routines and sleep quality.9,12,14–16 To give all children a fair chance at a healthy and happy life, we should seek to create an environment in which all children and adolescents are able to get the sleep they need.

In thIs Issue of SLEEP, GanGwIsch and col-leaGues 1 present a novel quasI-experImental analysIs that supports a causal relatIonshIp between chronic partial sleep deprivation and depression among adolescents. the positive association between chronic shortened sleep duration and depression is widely observed in the scientific literature. [2][3][4][5] although longitudinal data show that regular short sleep duration temporally precedes depression, 4 it is unclear whether it is a cause of depression, or a prodromal or comorbid symptom. In order to design interventions that reduce depression and suicidal ideation, we need to better understand the causal pathways through which they arise.
In the absence of conducting an unrealistic and ethically questionable experimental study that repeatedly restricts teenagers' sleep for long enough to potentially induce depressive symptoms, establishing a causal link presents a creative challenge to the researcher. the authors rise to the challenge by using parentally set bedtimes as a quasi-experiment, thereby taking advantage of a large nationally representative longitudinal study, add health. the idea is that parentally set bedtime is exogenous-not determined by the adolescent (nor his/ her depressive state)-and thus not at risk of having a reverse causal relationship in which depression causes the late nights and short sleep durations. If it were true that parents set their children's bedtimes based on their own parenting beliefs, and that such beliefs are unrelated to the depressive tendencies of an adolescent, then parental set bedtimes might act similarly to an experimental design in which parents are "randomly assigning" children to early and late bedtimes. operating on this identifying assumption, the authors find that adolescents with bedtimes past midnight are 24% more likely to have depression and 20% more likely to have suicidal ideation compared to those with bedtimes earlier than 10pm after adjustment for confounding variables. additional analyses show that the parentally set bedtime-depression relationship is attenuated by statistical adjustment of self-reports of sleep duration and perceptions of sleep sufficiency. These results suggest that the mediating pathway is indeed related to sleep duration and that sleep duration matters for mental health in teenagers.
the results of the analyses should be interpreted with some caution, however, because the use of parentally set bedtime does not fully satisfy the characteristics of a perfect exogenous force: there is likely some endogeneity between how adolescents behave and how parents set their bedtimes: parents may set bedtimes based on natural tendencies of the adolescent. for example, if a defiant teenager refuses to go to bed before midnight, a parent may know that it is fruitless to set a bedtime before 10 pm.
parents who enforce early bedtimes are likely to be different than parents who set later bedtimes in ways that aren't adjusted for in the analyses. that is, parents who set earlier bedtimes for their children may also have different household habits that are more conducive to reduced depression. Gangwisch et al. 1 partially address this concern by showing that adolescent perception of parent caring does not account for the reason why earlier bedtimes are associated with less depression.
finally, the presence of an early parentally set bedtime does not necessarily mean that it is enforced, nor that adolescents sleep more. to address these concerns, Gangwisch and colleagues present the remarkable finding that nearly 70% of adolescents report that they comply with their parent-determined bedtimes. It is less surprising, yet still important that the data show a strong relationship between earlier parentally set bedtimes and increased total sleep time.
despite the imperfect exogeneity of the parentally set bedtime measure, this work adds weight to the evidence that insufficient sleep may cause depression and suicidal ideation.
the study offers additional implications for adolescent health. In particular, this work shows that parentally mandated bedtimes actually do have a strong association with adolescent bedtimes and sleep duration. Given that regular high-quality sleep has been shown to have a wide range of positive outcomes on children and adolescents health and well-being, 6-8 as a result of this work, we can recommend parents continue to set bedtimes for their children through adolescence.
Gangwisch et al. 1 report that on average adolescents are sleeping 7 hours and 53 minutes, more than an hour less than the recommended 9 hours. thus, earlier bedtimes may not be enough, as a range of other factors affect adolescent sleep duration. for example, computer use and television watching are known to both delay time in bed and affect sleep quality. 9,10 future studies should investigate whether the implementation of other household routines (e.g., limiting electronics after 9 pm, restricting caffeine intake, and incorporating exercise into daily routines) can cause improvements in sleep and subsequent changes in mental and physical health.
there are a variety of community-level factors that can affect adolescent sleep. for example, school start time is associated with earlier wake times, and less total sleep time. 9,11,12 additional research into the relationship between adolescent sleep duration and depression should consider looking for variation in depression based on school start time, because school start time may serve as a better exogenous variable. Beyond school start time, adolescent schedules are driven by extracurricular activities, after-school employment, and social activities. policy and community efforts aimed at improving adolescent sleep should be explored.
Given a growing body of knowledge linking child and adolescent sleep to cognitive, behavioral, and health outcomes, this article raises a larger concern about sleep contributing social disparities in health. 6,7,13 starting early in life, social, economic, and neighborhood factors have an influence on sleep routines and sleep quality. 9,12,[14][15][16] to give all children a fair chance at a healthy and happy life, we should seek to create an environment in which all children and adolescents are able to get the sleep they need.

diSCloSure Statement
Dr. Hale has indicated no financial conflicts of interest.