We've told you that too little sleep raises the chance of obesity. Now, for the first time, there's a link between sleeping with artificial light at night and weight gain.
Using data from the nationwide Sisters Study, which predominantly examines breast cancer, federal scientists found that over 5 years, women sleeping with a light or the TV on were 17% more likely to have gained 10 pounds.
Outside light from outside the bedroom had a smaller link.
Study leaders suspect the light hampers the body clock and the sleep hormone melatonin.
They note that for many who live in urban environments, light at night is more common and should be considered.
They also add that humans are genetically set for a world on sunlight during the day and darkness at night.
Sleeping with light on at night may boost weight gain