Exposure to artificial light while sleeping may be a risk factor for weight gain and development of overweight or obesity, says a new study from the National Institute of Environmental Health Sciences (NIEHS).
“Although poor sleep by itself was associated with obesity and weight gain, it did not explain the associations between exposure to artificial light while sleeping and weight,” said Dr. Dale Sandler, senior author of the study.
“Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night,” added co-author Dr. Chandra Jackson.
“Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity.”
The study included women aged 35 to 74 years enrolled in the Sister Study in all 50 U.S. 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.
The study questionnaire asked whether participants slept with no light, a small nightlight, light outside of the room, or a light or television on in the room.
The scientists used weight, height, waist and hip circumference, and body mass index measurements taken at baseline, as well as self-reported information on weight at baseline and follow-up five years later.
Using this information, they were able to study obesity and weight gain in women exposed to artificial light at night with women who reported sleeping in dark rooms.
The results varied with the level of artificial light at night exposure.
For example, using a small nightlight was not associated with weight gain, whereas women who slept with a light or television on were 17% more likely to have gained 5 kg or more over the follow-up period.
The association with having light coming from outside the room was more modest.
“For many who live in urban environments, light at night is more common and should be considered,” Dr. Jackson said.
“Streetlights, store front neon signs, and other light sources can suppress the sleep hormone melatonin and the natural 24-hour light-dark cycle of circadian rhythms.”
“Unhealthy high-calorie diet and sedentary behaviors have been the most commonly cited factors to explain the continuing rise in obesity,” said Dr. Yong-Moon Park, first author of the study.
“This study highlights the importance of artificial light at night and gives women who sleep with lights or the television on a way to improve their health.”
The study was published in the journal JAMA Internal Medicine.
Yong-Moon Mark Park et al. Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women. JAMA Intern Med, published online June 10, 2019; doi: 10.1001/jamainternmed.2019.0571