Adolescent mental health: influences of early life adversity, pubertal timing, and sleep

Abstract

Adolescence is a time marked by physiological change and dynamic socioemotional development. It is also a period of changes to sleep patterns and a sharp increase in incident psychiatric conditions. Nationally representative data on high school students shows a rise in persistent feelings of depression and anxiety and alarming increases in suicidal ideation and attempts in the past decade. The work presented in this dissertation examines influences of early life adversity, pubertal timing, and sleep on adolescent psychiatric health and suggests an effective structural intervention to interrupt the chain of vulnerability to distress psychopathology among youth. Specifically, this dissertation aims to examine: 1) which developmental phenotypes most saliently mediate the relationship between early life adverse experiences and adolescent psychopathology; 2) how pubertal timing impacts sleep and depressed mood over the course of adolescence; and 3) how a structural policy to delay high school start times affects adolescent depression symptoms by prolonging weeknight sleep. The first study (Chapter 2) utilized an extensively characterized longitudinal sample of children to examine relative contributions of cognitive, affective, and developmental phenotypes as mediating mechanisms linking early-life adversity to adolescent psychopathology. While there is rich literature describing theory and evidence for consequences of early-life adversity, an empirical approach has not been to date applied to select mediators with the strongest relationships to dimensions of adversity – threat and deprivation – and adolescent externalizing and internalizing psychopathology symptoms. We used a high-dimensional mediation algorithm to narrow in on the strongest mechanisms from a set of 15 phenotypes. Blunted reward sensitivity mediated threat’s relationship to internalizing psychopathology. Early pubertal timing emerged as a robust predictor of greater internalizing and externalizing symptoms prospectively, although associations between pubertal timing and adversity expected based on prior literature were not identified. The second study (Chapter 3) interrogated the relationship between pubertal timing and depression symptoms, and examined sleep, which fundamentally changes during puberty, as a potential mechanism. We demonstrated temporal differences in associations between pubertal timing and depressed mood by sex but identified a sex-invariant mechanism by which earlier pubertal stage (specifically, more advanced pubic hair development, or adrenarche) impacts depression symptoms in late adolescence via a sustained loss of weeknight sleep duration. In the final study (Chapter 4), we leveraged a natural experiment of a high school start time delay to evaluate the effect of extended weeknight sleep duration on depressed mood over two years of follow-up. The delay decreased overall depression symptoms, in large part due to a substantial improvement in the fatigue and sleep-related cluster of symptoms. While the delay policy had no overall impact on the cluster of low mood and worry symptoms, we identified significant heterogeneity in the policy’s effect. Older students, who were heavier and aiming to lose weight, who exercised less, spent more time on screens, and consumed more caffeine saw greater improvements in mood than would be expected on average. Nonetheless, universal delay policy adoption was notably superior to attempts to optimize the policy to subgroups who benefit most, identifying the policy to delay high school start time as a potential structural intervention to safeguard adolescent mental health. The work assembled in this dissertation contributes to the epidemiologic literature on developmental risk factors for adolescent psychopathology by focusing largely on the impacts of pubertal timing and sleep health – understudied risk factors for depression symptoms in adolescent years. Together, the three studies suggest that structurally safeguarding adequate weeknight sleep duration in adolescence may improve population-level depression outcomes.