A study from the National Institute of Environmental Health Sciences found a link between one common nighttime habit and weight gain.
woman in bed sleeping peacefully
Credit: gorodenkoff/Getty Images

We'll be the first to admit we sometimes fall asleep with the TV on (we're not above late-night Netflix binges!) But it's just a harmless habit, right? The latest research says maybe not.

A study backed by the National Institute of Environmental Health Sciences found strong associations between sleeping with artificial light (be it a lamp or TV) and weight gain. What's more is that researchers accounted for various factors—such as sleep duration and quality, diet and exercise—but none of those factors could better explain the reason for their findings.

"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 Dale Sandler, Ph.D., one of the study's authors in a press release.

Researchers surveyed almost 43,000 American women between the ages of 35-74 from 2003 to 2009, and conducted a follow-up survey in 2015. None of these women had a history of cancer or cardiovascular disease when the study began, nor were they pregnant, daytime sleepers or shift workers. The study questionnaire asked whether the women slept with no light, a small nightlight, light outside of the room or a light or television on in the room.

The data from this study showed having any artificial light exposure at night while sleeping was positively associated with a higher prevalence of obesity at the beginning of the study and throughout. Compared with receiving no artificial light exposure at night while sleeping, exposure was associated with gaining about 11 pounds and increasing BMI by 10 percent.

The only exception here was those who slept with a small nightlight. Those who slept with one did not seem to experience the same kind of weight patterns as those who slept with larger lights or the TV on.

"Unhealthy high-calorie diet and sedentary behaviors have been the most commonly cited factors to explain the continuing rise in obesity," said lead author Yong-Moon Park, M.D., Ph.D. "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 Bottom Line

The researchers make it clear their findings depict an association rather than cause-and-effect evidence. More research needs to be done on the subject to back up the results they found.

However, loads of studies have been depicting a relationship between sleep and our overall health. Low-quality sleep, or not getting enough of it, has shown to increase our risk for obesity and various chronic diseases. And sleeping with artificial light may not be doing us any favors to help us reach that deep sleep our bodies need! It might be worth setting a timer on your TV at night, or ditching the habit entirely, to help you get some shuteye.