Light at night exposure and risk of depression and other mental disorders: a systematic review

Background In modern society, individuals are increasingly exposed to artificial light at night (LAN) i.e., different sources of light altering the natural day-night cycle. Emerging evidence suggests a possible association between LAN exposure and physiological and behavioral changes, with implications on mood and mental health at the population level. We performed a systematic review of observational studies to investigate if LAN exposure, may be associated with an increased risk of mental diseases in humans. Methods/Approach We reviewed the epidemiological evidence about the association between LAN exposure as assessed either via satellite photometry (outdoor LAN) or via measurements of bedroom brightness (indoor LAN), and risk of mental disorders. We systematically searched the PubMed, Embase and Web of Science databases up to September 1, 2022. Studies were included if they assessed the link between exposure to indoor or outdoor LAN and one or more mental disorders. Results Ten 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. Studies were published between 2002 and 2022. Eight studies were conducted in adult populations, one in adolescents, and one in children. Mental disorders investigated include anxiety and mood disorders, depression, bipolar disorder, autism and mild cognitive impairment. 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 air 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 risk of depressive disorders.