Do you fall asleep with the TV on? Maybe have an alarm clock that's a bit too bright? Well, according to a new study, that could be making you fat.

The National Institutes of Health's study, which was published online June 10 in JAMA Internal Medicine, is said to be the first of its kind; it examined the effects artificial light on women's waistlines.

More than 43 thousand woman aged 35-74 took part in the Sister Study; they answered a questionnaire regarding their sleep habits. They were asked if they slept with no light, a small nightlight, a light or television on in the room, or if there was light outside of the room.

Correlating that data with BMI and other measurements, the females' weights were recording as a baseline, and then five years later -- and the women that slept without the intrusion of artificial light maintained their weights better than those who did not.

Interestingly, the results varied with how much light in the room: women who slept with a light or a TV on -- the brightest light -- were 17% more likely to have gained as 11 pounds in that five years; women who only slept with a small nightlight were better able to maintain their weight.  

"Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night," said study co-author Chandra Jackson, Ph.D. said in a release. "Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity."

So, get some blackout curtains and a sleep mask, STAT. They're less expensive than a new wardrobe!

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