Exposure to Light at Night Could Lead to Weight Gain, Obesity

A new study has found that consistently being exposed to light at night can lead to obesity and weight gain, even if an individual isn’t eating more food or changing their physical activity. Researchers from Ohio State University found that mice exposed to dim light at night over a period of eight weeks gained about 50 percent more weight than mice that weren’t exposed to light.

Laura Fonken, a doctoral student in neuroscience at Ohio State University and lead author of the study, said that although both sets of rats ate the same amount of food and had the same amount of daily activity, the mice who were exposed to light gained more weight than the others. This could be because the light-exposed mice eat on different schedules.

In one study, light-exposed mice that were restricted to a normal eating schedule didn’t gain more weight than mice that weren’t exposed to light. Randy Nelson, co-author of the study and professor of neuroscience and psychology at Ohio State University, said that the light at night was prompting the mice to eat at abnormal times. If this is replicated in humans, it would suggest that late-night eating could be a risk factor for obesity.

In another study, mice were kept in three lighting conditions: 24 hours of constant light, 16 hours of light and 8 hours of dark (normal light/dark cycle), or 16 hours of light and 8 hours of dim light. The researchers tracked how much food the mice ate and their daily activity, and they calculated body mass index once per week.

The mice that were exposed to dim light at night had significantly higher weight gain from the first week and throughout the rest of the study. They gained about 12 grams of body fat whereas those in the standard cycle gained 8 grams. Mice exposed to constant light also gained more than those in the standard cycle, but the researchers noted that the dim light exposure was more comparable to the light exposure humans usually have.

While the dim-light mice did not eat more than other mice, they ate 55 percent of their food during the day, compared to the standard cycle mice that ate 36 percent of their food during the day. These mice normally would eat most of their food at night because they are nocturnal.

In another experiment, food was restricted to times when the mice would normally be active or at rest. Dim-light mice did not gain more weight than the others when their food was restricted to times when they would usually be active. Fonken said that this suggested that the time of day when eating occurs plays an important role in weight gain.

They also found that levels of the stress hormone corticosterone did not change among the mice. Because corticosterone has been associated with changes in metabolism, this suggests that changes in corticosterone levels weren’t necessary for changes in metabolism in the mice.

The researchers think the light at night could disrupt levels of the hormone melatonin, which plays a role in metabolism. It could also disrupt “clock genes,” which control when animals eat and when they are active.

Nelson said that their study suggested that light at night could be contributing to the epidemic of obesity in an unexpected way.

Source: Science Daily, Too Much Light at Night at Night May Lead to Obesity, Study Finds, October 11, 2010

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