Research by the Ohio State University has found that persistent exposure to light at night may lead to weight gain, even without changing physical activity or eating more food.
By studying mice the researchers found that mice exposed to a relatively dim light at night over eight weeks had a body mass gain that was about 50 percent 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 doctoral student in neuroscience at Ohio State University.
The study appears this week in the online early edition of the Proceedings of the National Academy of Sciences.
As they’re not less active or eating more, the results suggest that the weight gain is because the mice living with light at night eat at times they normally wouldn’t.
In one study, mice exposed to light at night – but that had food availability restricted to normal eating times – gained no more weight than did mice in a normal light-dark cycle.
“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.
If these results are confirmed in humans, it would suggest that late-night eating might be a particular risk factor for obesity, Nelson said.
Mice exposed to dim light-at-night showed higher levels of epididymal fat, and impaired glucose tolerance – a marker of pre-diabetes.
“When we restricted their food intake to times when they would normally eat, we didn’t see the weight gain,” Fonken said about the mice. “This adds to the evidence that the timing of eating is critical to weight gain.”
So how does light at night lead to changes in metabolism? The researchers believe the light could disrupt levels of the hormone melatonin, which is involved in metabolism. In addition, it may disrupt the expression of clock genes, which help control when animals feed and when they are active.
Overall, the findings show another possible reason for the obesity epidemic in Western countries.
Researchers have long associated prolonged computer use and television viewing as obesity risk factors, but have 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,” 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 research was supported by the National Science Foundation and the U.S.-Israel Binational Science Foundation for the Ohio State University.
