Keeping a lot of light on while you snooze—such as from a television or bright nightlight—has been linked with an increased risk of weight gain and obesity.
Specifically, sleeping with a television or light on in the room was positively associated with gaining five kilograms, or 11 pounds, over a five-year period among women in a new study published in the medical journal JAMA Internal Medicine on Monday.
“There was a 17 percent chance of gaining the five kilograms, after we adjusted for confounding factors,” said Dale Sandler, a senior investigator at the National Institute of Environmental Health Sciences in North Carolina and senior author of the study.
In addition, there was a 22 percent chance of becoming overweight and a 33 percent chance of becoming obese, she added.
Obesity means having too much body fat and overweight means weighing too much, according to the US National Library of Medicine. Both overweight and obesity are based on your body mass index but “obese” generally means having a much higher BMI.
“We are in the middle of an obesity epidemic in the United States and the things that we usually think about for obesity prevention are hard for people to do—eat a better diet, get more exercise—and we don’t seem to be making a dent,” Sandler said. “If these study findings are true and if they can be replicated then it’s a very easy public health message to turn off the lights when you’re sleeping.”
The study involved analyzing data on 43,722 women, aged 35 to 74, in the United States.
The data came from a nationwide cohort study called the Sister Study that enrolled women between 2003 and 2009. The data included information on each woman’s sleeping habits, such as if she slept with a small nightlight or a television on, and her body mass index.
Body mass index or BMI, a calculation derived from a person’s weight and height, can be used as a screening tool for body fatness and obesity risk. A normal or healthy BMI is typically considered to be between 18.5 and 24.9. A BMI of 30 and higher is considered to be obese.
The women’s self-reported sleeping habits were put into four categories: no light, small nightlight in the room, light outside of the room, and light or television in the room.
Women who reported more than one type of artificial light were categorized at the highest level of exposure. Women who slept with a mask on or reported no light while sleeping were classified as experiencing no artificial light exposure.
The researchers took a close look at each woman’s sleeping habits and her weight and obesity risk over a five-year period.
Among the women, the researchers found that sleeping with a television or light on in the room was associated with gaining five kilograms or more, a BMI increase of at least 10 percent, and a higher risk of being overweight or obese, compared with being exposed to no artificial light during sleep.