Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women

Key PointsQuestionIs artificial light at night while sleeping associated with weight gain and obesity? FindingsIn this cohort study of 43722 women, artificial light at night while sleeping was significantly associated with increased risk of weight gain and obesity, especially in women who had a light or a television on in the room while sleeping. Associations do not appear to be explained by sleep duration and quality or other factors influenced by poor sleep. MeaningExposure to artificial light at night while sleeping appears to be associated with increased weight, which suggests that artificial light exposure at night should be addressed in obesity prevention discussions. This cohort study assesses whether exposure to artificial light at night while sleeping is associated with the prevalence and risk of general and central obesity among women. ImportanceShort sleep has been associated with obesity, but to date the association between exposure to artificial light at night (ALAN) while sleeping and obesity is unknown. ObjectiveTo determine whether ALAN exposure while sleeping is associated with the prevalence and risk of obesity. Design, Setting, and ParticipantsThis baseline and prospective analysis included women aged 35 to 74 years enrolled in the Sister Study in all 50 US states and Puerto Rico from July 2003 through March 2009. Follow-up was completed on August 14, 2015. A total of 43722 women with no history of cancer or cardiovascular disease who were not shift workers, daytime sleepers, or pregnant at baseline were included in the analysis. Data were analyzed from September 1, 2017, through December 31, 2018. ExposuresArtificial light at night while sleeping reported at enrollment, categorized as no light, small nightlight in the room, light outside the room, and light or television in the room. Main Outcomes and MeasuresPrevalent obesity at baseline was based on measured general obesity (body mass index [BMI] >= 30.0) and central obesity (waist circumference [WC] >= 88 cm, waist-to-hip ratio [WHR] >= 0.85, or waist-to-height ratio [WHtR]>= 0.5). To evaluate incident overweight and obesity, self-reported BMI at enrollment was compared with self-reported BMI at follow-up (mean [SD] follow-up,5.7 [1.0] years). Generalized log-linear models with robust error variance were used to estimate multivariable-adjusted prevalence ratios (PRs) and relative risks (RRs) with 95% CIs for prevalent and incident obesity. ResultsAmong the population of 43 722 women (mean [SD] age, 55.4 [8.9] years), having any ALAN exposure while sleeping was positively associated with a higher prevalence of obesity at baseline, as measured using BMI (PR, 1.03; 95% CI, 1.02-1.03), WC (PR, 1.12; 95% CI, 1.09-1.16), WHR (PR, 1.04; 95% CI, 1.00-1.08), and WHtR (PR, 1.07; 95% CI, 1.04-1.09), after adjusting for confounding factors, with P<.001 for trend for each measure. Having any ALAN exposure while sleeping was also associated with incident obesity (RR, 1.19; 95% CI, 1.06-1.34). Compared with no ALAN, sleeping with a television or a light on in the room was associated with gaining 5 kg or more (RR, 1.17; 95% CI, 1.08-1.27; P<.001 for trend), a BMI increase of 10% or more (RR, 1.13; 95% CI, 1.02-1.26; P=.04 for trend), incident overweight (RR, 1.22; 95% CI,1.06-1.40;P=.03 for trend), and incident obesity (RR, 1.33; 95% CI, 1.13-1.57; P<.001 for trend). Results were supported by sensitivity analyses and additional multivariable analyses including potential mediators such as sleep duration and quality, diet, and physical activity. Conclusions and RelevanceThese results suggest that exposure to ALAN while sleeping may be a risk factor for weight gain and development of overweight or obesity. Further prospective and interventional studies could help elucidate this association and clarify whether lowering exposure to ALAN while sleeping can promote obesity prevention.