Hormones, Circadian Rhythms, and Mental Health

Circadian rhythms permit adaptations to predictable temporal environmental changes. Daily 24-hour rhythms are controlled by molecular clockworks within the brain that are set by the daily light–dark cycle. Downstream endocrine signaling conveys temporal information throughout the body. Mood disorders often present with disruptions in circadian clock-controlled responses, such as sleep and cortisol secretion, whereas circadian rhythm disruptions via jet lag, night-shift work, or light at night increase disordered affective symptoms. Evidence suggests strong associations between circadian rhythms and mental health, but only recently have studies begun to discover the direct interactions between the circadian system and mood regulation. This chapter provides an overview of circadian rhythms and the circadian regulation of the endocrine system. It discusses how the circadian and endocrine systems interact to affect depressive, anxious, and addictive responses. Finally, it discusses the potential detrimental effects the widespread use of nighttime light has for mood and cognition.