BACKGROUND: Daylight exposure is crucial to synchronize our circadian system, which is essential for physical and mental health. Modern lifestyle changes, however, have resulted in reduced time spent outdoors in daylight, potentially leading to mood disturbances. This study investigated the association between time spent outdoors in daylight and depression prospectively, including potentially moderating effects of age, sex, and chronotype.
METHODS: A prospective, population-based cohort study embedded in Lifelines in which 70,827 people aged 18-89 years were followed-up for 2.5 years. Daylight exposure was measured as time spent outdoors in daylight with the Munich ChronoType Questionnaire (MCTQ). Major Depressive Episodes were assessed at baseline and follow-up with the Mini International Psychiatric Interview (MINI). Generalized Additive Models (GAM) were used to capture non-linearity and adjusted for potential confounders. Moderation analyses were conducted with interaction terms for age, sex, and chronotype.
RESULTS: No significant association was found between the amount of hours of daylight exposure and future depression status in the general population, nor any interaction with age or sex. However, increased daylight exposure was associated with lower odds of depression 2.5 years later in individuals with late chronotypes (7% decrease per hour, 95% CI: 0.87 - 0.99).
CONCLUSIONS: Although time spent outdoors appears not to be associated with depression after 2.5 years in the general population, it may help decrease the risk for depression for late chronotypes. Tailored daylight exposure recommendations based on chronotype may enhance mental health outcomes. Further studies are needed to explore the role of the timing of daylight exposure.
Keywords: Depression; Natural light; Daylight; Chronotype; Circadian Rhythms