Artificial light at night and risk of mental disorders: A systematic review

Background: Emerging evidence suggests a possible association between artificial light at night (LAN) exposure and physiological and behavioral changes, with implications on mood and mental health. Due to the increased amount of individuals' LAN exposure, concerns have been raised regarding harmful impact of LAN on mental health at the population level. Aim: To perform a systematic review of observational studies to investigate if light-at-night, assessed both indoor and outdoor, may be associated with an increased risk of mental diseases in humans. Methods: We reviewed the epidemiological evidence on the association between LAN exposure, assessed either via satellite photometry or via measurements of bedroom brightness, and mental disorders. We systematically searched the MEDLINE, Embase and Web of Science databases up to April 1, 2022. Studies were included if they assessed the link between indoor or outdoor artificial light at night and one or more mental disorders in human populations. Results: Nine eligible studies were included in this review: six studies had a cross-sectional design, two had a longitudinal design with a median follow-up of 24 months, and one was a case-cohort study. Overall, we found moderate evidence of a positive association between LAN exposure and depressive symptoms and to a lesser extent other mental disorders, though the number of studies was limited and potential residual confounding such as socioeconomic factors, noise, or pollution may have influenced the results. Conclusions: Although more robust evidence is needed, the epidemiological evidence produced so far seems to support an association between LAN and depressive disorders. Keywords: Depression; Environmental risk factors; Light-at-night; Mental disorders; Systematic review.