A large observational study suggests exposure to artificial light at night while sleeping raises risk for obesity.
Animal and limited human data indicate that exposure to artificial light at night (ALAN) contributes to obesity. As part of a prospective U.S. cohort study, 43,222 women (mean baseline age, 55) were asked about sources of ALAN present while sleeping, including no light (Category 1 [C1]), a nightlight or clock radio (C2), light from outside the room (C3), or a television or ≥1 light on in the room (C4). Body-mass index (BMI) was measured at baseline and every 2 to 3 years. Baseline mean BMI progressively increased with ALAN exposure, from 27.0 kg/m2 (C1 and C2) to 29.2 (C4).
Exposure to ALAN may suppress melatonin production, disrupting circadian rhythms. However, as the authors also note, ALAN exposure while sleeping may simply reflect socioeconomic disadvantage and unhealthy lifestyles associated with obesity. Either way, counseling the patients to minimise nighttime exposure to artificial light seems eminently reasonable.