Sleeping with the lights on may increase the risk for obesity.
Researchers prospectively followed 43,722 generally healthy women, average age 55, for an average of six years. At enrollment in the study, the women reported whether they slept with lights or a television on in the room. Those who slept with artificial light had higher body mass index and larger waist circumference than those who slept with no light.
But after controlling for these factors, as well as for age, race, physical activity, diet, sleep duration and other variables, they found that sleeping with lights on was independently associated with gaining 11 pounds or more, an increase of 10 percent or more in B.M.I., a 22 percent increased risk for being overweight and a 33 percent increased risk for obesity. The study is in JAMA Internal Medicine.
The mechanism is unclear, but the researchers suggest that light may disrupt sleep enough to change levels of appetite-regulating hormones or cause daytime sleepiness that reduces physical activity.
“Getting a good night’s sleep is really important for health,” said the senior author, Dale P. Sandler, an epidemiologist with the National Institutes of Health. “A very simple thing people can do to reduce the risk for obesity is to turn off the lights before going to sleep.”