Women who slept with a light or even the TV on were 17% more likely to have gained 11 pounds over the course of five years, according to the study, the results of which were published Monday in the medical journal JAMA Internal Medicine.
Light coming in from outside the room was associated with more modest weight gain, researchers found.
The study is the first to find an association between exposure to artificial light at night while sleeping and weight gain in women, according to the National Institutes of Health (NIH), which funded the study.
More than 43,000 women in the U.S. ages 35 to 74 were observed in the study.
One of the factors pointed to by researchers is that light could suppress the sleep hormone melatonin and disrupt our circadian rhythms, according to ABC News chief medical correspondent Dr. Jennifer Ashton.
Ashton suggests that women create a prime sleeping environment for themselves by using tools like eye masks and blackout shades or drapes. People should also turn off all electronics in their bedroom and dim their alarm clocks to avoid the glare of any bright lights.
This sleep study comes on the heels of another study that found irregular sleep patterns, including not going to bed and waking up at the same time each day or getting different amounts of sleep each night, can put people at a higher risk for obesity, heart disease, hypertension, high blood sugar and other metabolic disorders.
That means the bedtimes advised for children may be a good thing to implement well into adulthood, too.
"Sleep has a [public relations] problem in this country," Ashton said on "Good Morning America" last week. "We look at it like a luxury. It is a medical necessity on par with our food and our fitness."
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