Is artificial light at night while sleeping associated with weight gain and obesity?
In this cohort study of 43 722 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. Exposure 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. Short 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. To determine whether
ALAN exposure while sleeping is associated with the prevalence and risk of obesity.
This 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 43 722 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. Artificial 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. Prevalent 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. Among 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. These 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.