Artificial light and the circadian rhythm: Sleeping with a TV or light on linked to weight gain, reveals study
01/29/2020 // Darnel Fernandez // Views

After a long day of work, many people might find themselves watching a show before they fall asleep. However, if you manage to fall asleep while leaving the television on, it might lead to some negative consequences on your health.

A study published in the journal JAMA Internal Medicine found that exposure to artificial light while sleeping can influence weight gain in women. This is the first study to find such association and the findings suggest that cutting off the lights at bedtime can significantly reduce the chances of becoming obese.

The link between obesity and your circadian rhythm

Previous research has established that short sleep has always been associated with obesity. However, the association between exposure to artificial light at night while sleeping and obesity has not been explored much. For this study, researchers from the National Institute of Environmental Health Sciences (NIEHS) aimed to determine whether exposure to this artificial light could influence the prevalence and risk of obesity.

To do so, the research team analyzed questionnaire data from 43,722 women aged 35-74 years enrolled in the Sister Study, a cohort study that studies risk factors for breast cancer and other diseases. Each of the women had no history of cardiovascular disease or cancer and were not shift workers, daytime sleepers or pregnant at the beginning of the trial. The questionnaire given asked about the women's sleep habits, including whether they slept with no light, a small nightlight, light outside the room or light or television on inside the room.


Further, the research team gathered measurements for height, waist and hip circumference, weight and body mass index at the start of the trial. They also asked the participants' to provide a self-report on weight both at baseline and after a five-year follow-up. Using all the information gathered, the researchers were able to study obesity and weight gain in women exposed to artificial light at night and women who reported sleeping in completely dark rooms. (Related: Could artificial light be making you fat? Or even worse, giving you cancer?)

The researchers divided light exposure into four categories: Those who slept in complete darkness, those who sleep with a small night light, those who had a light on outside the bedroom, and those who slept with an open television or light in the room. The results of the analysis varied between these four categories.

The findings show that women who slept with a light or television on saw the greatest likelihood of gaining weight by far, with a 17 percent increased chance to gain five kilograms or 11 pounds. Those who slept with a small nightlight on did not gain weight whatsoever, while women who slept with lights on in another room had a far more modest effect, seeing only a 3 percent increased likelihood to gain that extra five kilograms.

The researchers also theorized whether not getting enough rest could be factored into their findings but came up short.

"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," Dale Sandler Ph.D., chief of the Epidemiology Branch at the NIEHS and senior and corresponding author of the study, said.

Co-author Chandra Jackson, head of the NIEHS Social and Environmental Determinants of Health Equity Group, noted that people living in urban environments often experience consistent artificial light at night and should be considered. Artificial lights such as storefront neon lights, street lights and other forms of light sources can suppress the sleep hormone melatonin and disrupt the natural 24-hour light-dark cycle of circadian rhythms.

"Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night," Jackson said. "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 researchers concluded that exposure to artificial light at night can be a major risk factor for weight gain and the development of obesity. They suggest that future studies could help make this association clear and see whether lowering exposure to these artificial lights while sleeping could promote obesity prevention.

Learn more about other ways that cause obesity at

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