Exposure to light at night doesn't just mess with your quality of sleep; it may also result in extra pounds, according to a new study published in theAmerican Journal of Epidemiology.
Researchers asked 113,000 women to rank the amount of light in their bedrooms, from "light enough to read" to "too dark to see your hand.
" The research team then compared the answers to the study subjects' body mass indexes (BMIs), waist-to-hip ratios, and waist-to-height ratios. The result: All three obesity measures were higher among women who were exposed to light while trying to sleep, and the more light in the room, the heavier the woman who slept there was likely to be. This link persisted even after researchers controlled for potentially mitigating factors, such as how long the women slept and their physical activity levels.The idea that light can affect weight isn't exactly new; previous animal studies have suggested that nocturnal light may trigger metabolic changes resulting in extra fat and body mass, even when calorie intake and physical activity is constant. But the new study is one of the few that have ID'd this connection in humans. "We've known that exposure to light probably affects production of the hormone melatonin, which helps regulate sleep," says Michael Breus, Ph.D., clinical psychologist and diplomate of the American Academy of Sleep Medicine, who was not involved with the study. "Melatonin in turn affects other hormones, and these could play a role in changing appetite, altering glucose metabolism, and inducing hunger."
More research needs to be done before a definitive cause and effect can been shown between light and BMI. In the meantime, it's not a bad idea to unplug the nightlight and redecorate with room-darkening shades if you're watching the scale. "Sleeping in darkness leads to deeper sleep and less sleep deprivation," says Breus. "More restful sleep has a positive effect on your entire system, and that theoretically includes your weight."
