Sleeping with light on may lead to weight gain

Too much light at night appears to lead to weight gain, according to an American study of mice, by changing eating patterns.

The researchers found that mice exposed to a dim light at night over eight weeks had a weight gain that was about 50% more than other mice that lived in a standard light-dark cycle.

"Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others," said Laura Fonken, lead author of the study and a researcher at Ohio State University.

Could light affect metabolism?

The study, which appears in the journal Proceedings of the National Academy of Sciences, said the weight gain could be a sign that light has an effect on the metabolism.

"Something about light at night was making the mice in our study want to eat at the wrong times to properly metabolize their food," said Randy Nelson, co-author of the study and professor of neuroscience and psychology at Ohio State.

In humans, it would suggest that late-night eating might be a particular risk factor for obesity, Nelson said.