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Originally published October 27 2010

Turn off the lights when you go to bed - Even dim light at night may trigger obesity

by S. L. Baker, features writer

(NaturalNews) You are getting the same amount of exercise as always, you aren't taking in any more calories than usual and yet you keep on gaining weight. So you may be wondering what on earth is going on with your body. Maybe the question you should be asking yourself is this one: what lights are on in your bedroom at night? According to new research, persistent exposure to light at night may lead to weight gain, even without decreasing physical activity or eating more food.

The study, just published in the online edition of the Proceedings of the National Academy of Sciences, involved animals. However, the findings raise serious questions about whether the human body is also at risk from altered metabolism and weight gain from too much light exposure at night.

An Ohio State University research team found that mice exposed to a fairly dim light at night over about a two month period experienced a gain in body mass that was approximately 50 percent more than other mice who lived and slept in a normal 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," Laura Fonken, a doctoral student in neuroscience at Ohio State who headed the study, said in a statement to the media.

Although the lab mice exposed to night time light were not less active and didn't eat more, they were found to eat at times when they normally wouldn't be chowing down. In fact, in one study when mice exposed to light at night were restricted from eating except at their normal feeding times, they did not experience extra weight gain.

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

The researchers found that levels of the stress hormone corticosterone were not significantly different in the mice exposed to the dim light when compared to the mice living in a standard light-dark cycle. That was surprising because corticosterone has been linked to changes in metabolism. So the mice research showed there could be changes in metabolism causing weight gain without changes in corticosterone levels.

But how could dim light at night be triggering fat-causing changes in metabolism? The Ohio State scientists think the light may be disrupting levels of the hormone melatonin, which plays an important role in metabolism. Moreover, light exposure at night may disrupt the expression of clock genes, which help control when animals eat and when they are active.

Dr. Nelson stated that if these results are confirmed in people that could mean eating late at night might be a serious risk factor for obesity. "Light at night is an environmental factor that may be contributing to the obesity epidemic in ways that people don't expect," he said. "Societal obesity is correlated with a number of factors including the extent of light exposure at night."

Previously, researchers have targeted prolonged computer use and television viewing as risk factors for obesity -- but they've focused on how watching TV or surfing the Internet for hours on end contribute to a lack of physical activity. Instead, the link between being overweight and using the computer and watching TV a lot at night could hinge more on the association with too much light at night and eating at the wrong time, which disrupts 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," Dr. Nelson concluded in a press statement.

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