Before you crawl into bed tonight, turn off the lights and turn off your devices. According to new research published in JAMA Internal Medicine, exposure to artificial light – from light sources such as overhead lights, smartphones and televisions – is associated with higher rates of obesity.
The study, which included nearly 44,000 women between the ages of 35 and 74 over a six-year period, found that women who were exposed to artificial light while sleeping had a 17 percent higher risk of gaining about 11 pounds compared to those who slept in the dark; they had a 33 percent higher rate of obesity. Women who slept with the TV or lights on were also more likely to gain weight and become overweight or obese over time.
“Humans are genetically adapted to be active during the day and sleep in the dark at night,” explains lead author Yong-Moon (“Mark”) Park, PhD, a postdoctoral researcher at the National Institutes of Health.” Exposure to light while sleeping at night may alter the body’s 24-hour body clock, leading to changes in hormones and other biological processes that regulate sleep, appetite, and weight gain.”
While the study focused on exposure to artificial light in the bedroom, Park noted that light from outside the room – such as from other rooms or streetlights – was also associated with a slightly increased risk of weight gain. The study did not explore whether overall exposure to artificial light, including daytime exposure, had an effect on weight.
Some studies have linked sleep problems, including insomnia, sleep duration and interrupted sleep, to higher rates of obesity. Research published in the journal Sleep Medicine found that people who slept less than six or more than nine hours per night had higher rates of obesity; one study showed that chronic insomnia was also associated with a higher BMI.
The link between sleep and obesity is one reason that makes improving sleep a priority, says Lucci, MD, PhD, director of the Center for Obesity Research at Tulane University. But sleep is just one of the known risk factors for obesity. Lifestyle factors such as unhealthy diet, sedentary lifestyle, stress, and smoking have also been linked to an increased likelihood of being overweight or obese.
“Even if you improve your sleep habits, you still need to be aware of other risk factors,” says Qi.” We also need to be cautious in interpreting these results; artificial light may be a factor, but it may be associated with other habits that were not part of this study.”
Park agrees, adding, “While our study provides stronger evidence than other previous studies, it’s still not conclusive. Even so, it seems reasonable to suggest that people should not sleep with the lights on. Turning off the lights while sleeping may be a simple thing we can do to reduce the chances of gaining weight.”