Having Lights on at Night May Be Making You Fatter

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Having electric light available at all times during the night is one of those luxuries we have taken for granted in our modern age -- but the results of a new study suggest that a well-lit house at night might actually be making you fatter. Working with mice, researchers from Ohio State University found that subjects gained more weight when exposed to persistent light at night compared to those who didn't, despite the fact they received the same amount of food and exercise.

According to the study, researchers found that mice who had food available at all times didn't eat more food when exposed to a dim light during the evening, but instead they ate at unusual times -- like midnight snacking. "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 professor of neuroscience, Randy Nelson, to PhysOrg.

To study the relationship between weight-gain and nighttime lighting, researchers placed groups of mice in differently lit conditions and monitored their body mass over an eight week period. Some mice were exposed to 24 hours of normal lighting, another to 16 hours of normal light and 8 hours of dimness. The third group received a standard light-dark cycle (16 hours light, eight hours darkness).

The study noted that the group exposed to dim light at night best represented the conditions of many people live with. Results showed that the mice in this group gained 50 percent more body mass than those in the normal light-dark cycle that nature intended -- and they did it without eating more food than the others.

Researchers found that the persistent exposure to light, even when dim, changed the eating habits of the mice quite significantly -- meaning they consumed 20 percent more food during their off-hours than the mice with periods of both light and dark. It would seem that the animals' metabolism is affected by the light, as is the internal clock that normally dictates feeding patterns.

This has obviously implications for a culture that has grown accustomed to the bright lights that fill rooms at night all across the western world. Nelson explains:

Light at night is an environmental factor that may be contributing to the obesity epidemic in ways that people don't expect. Societal obesity is correlated with a number of factors including the extent of light exposure at night.
It may be that people who use the computer and watch the TV a lot at night may be eating at the wrong times, disrupting their metabolism. Clearly, maintaining body weight requires keeping caloric intake low and physical activity high, but this environmental factor may explain why some people who maintain good energy balance still gain weight.

If reducing your carbon footprint wasn't reason enough to switch off the lights at night, perhaps the prospect of slimming your waistline will.