Time spent outdoors in daylight and depression risk after 2.5 years: Insights from the Lifelines cohort

BACKGROUND: Daylight exposure is crucial to synchronize our circadian system, which is essential for physical and mental health. This study prospectively examined the association between time spent outdoors in daylight and depression, 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. Time spent outdoors in daylight was assessed with the Munich Chronotype Questionnaire (MCTQ). Major Depressive Episodes were assessed at follow-up with the Mini International Psychiatric Interview (MINI). Generalized Additive Models (GAM) were used to assess the potentially non-linear association, adjusting for relevant confounders. Moderation was tested via interaction terms for age, sex, and chronotype, and if significant, subgroup analyses were performed. If GAM indicated a (close to) linear association, logistic regression was done.

RESULTS: No significant association was found between the amount of hours of daylight exposure and future depression status, nor any interaction with age or sex. However, there was a significant interaction with chronotype, and increased daylight exposure was linearly associated with lower odds of depression 2.5 years later in late chronotype individuals (OR 0.93, 95 % CI: 0.87-0.99).

CONCLUSIONS: Time spent outdoors was not associated with depression after 2.5 years in the whole group, but the odds for late chronotypes were 7 % lower for each additional hour of daylight. Tailored daylight exposure recommendations based on chronotype may support mental health. Further studies are needed to explore the role of the timing of daylight exposure.