A study, published in the journal JAMA Internal Medicine, is the first to find an association between any exposure to artificial light while sleeping to an increase in weight in women. The results suggested that cutting off lights at bedtime could potentially reduce women’s chances of becoming obese.Lead author Yong-Moon Park said, “The research suggests a viable public health strategy to reduce obesity incidence in women.” The study’s 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 scientists used weight, height, waist and hip circumferences and body mass index measurements taken at baseline, as well as self-reported information on weight at baseline, with a follow-up five years later to study obesity and weight gain in women exposed to artificial light at night with women slept in dark rooms.
The results varied with the level of exposure to artificial light at night. For example, using a small night light was not associated with weight gain, whereas women who slept with a light or television on were 17 per cent more likely to have gain at least 5 kilograms or more over the follow-up period.
Co-author Chandra Jackson noted that for many who live in urban environments, a light at night is more common and should be considered. Streetlights, storefront neon signs, and other light sources can suppress the sleep hormone melatonin and 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, they added.