Healthy living

Too much light at night may lead to weight gain

Too much light at night may lead to weight gain Disrupts eating times

Too much light at night may lead to weight gain, according to new research.

Researchers found that mice exposed to a relatively dim light at night over eight weeks gained around 50 percent more weight than mice that lived in a standard light-dark cycle. But both groups of animals ate the same amount of food.

“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, a neuroscientist at Ohio State University.

So what caused the weight gain?

The mice were housed in one of three conditions; 24 hours of constant light; a standard light-dark cycle - 16 hours of light, 8 hours of dark; or 16 hours of daylight and 8 hours of dim light.

Mice which were kept in the dim light started putting on significantly more weight from the first week and throughout the study.

By the end of the eight weeks, the dim light mice had increased their weight by 12g compared to 8g for those living in the standard light-dark cycle.

The dim light mice also had higher levels of epididymal fat, and impaired glucose tolerance – a marker of pre-diabetes.

Although mice sleeping in the dim light didn’t eat more than others, they changed when they ate, the researchers found.

Mice are nocturnal, and normally eat more food at night. But the mice which slept in dim light ate 55 per cent of their food during the daylight hours, compared to only 36 per cent in the mice living in a standard light-dark cycle.

Study co-author Professor Randy Nelson said: “Something about light at night was making the mice in our study want to eat at the wrong times to properly metabolise their food.”

If the results were confirmed in humans, it would mean that late-night eating might be a particular risk factor for obesity, he added.

Other research has identified prolonged computer use and television viewing as risk factors for obesity, but has focused on how they are associated with a lack of physical activity.

“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,” Dr Nelson said.

“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.”

The dimmed light could disrupt levels of melatonin, a hormone involved in metabolism, the researchers said. It may also disrupt the expression of clock genes, which help control when animals feed and when they are active.

The findings are published in the Proceedings of the National Academy of Sciences

This article was published on Tue 12 October 2010

Image © Valua Vitaly -

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