Too much junk food and lack of exercise makes us pudgy. But new research out of Ohio State University suggests there may be another factor at play: too much light at night.
“We were looking at the increasing level of obesity and realized that light at night -- and by that I mean electricity, TV viewing at night, people using computers later at night ... has also been increasing,” says Laura Fonken, a neuroscientist at Ohio State University in Columbus and lead author of the study.
To see if there was a connection, Fonken and her colleagues conducted a series of experiments exposing laboratory mice first to 16 hours of light and then eight hours of either total darkness, dim light -- like you’d get if the TV was on in your bedroom -- or full bright light. The result? The mice that “watched TV” all night gained weight. It was the same with the mice exposed to bright light all night long.
It didn’t take long for the pounds to pile up, either.
“After one week, the body mass increased with the mice with light at night and continued to increase throughout the eight-week study,” Fonken says. By the end of the study, the mice in the light cycle had about a 50 percent increase in weight compared to mice in the dark.
You might think the mice that were staying up late were chowing down on food more than the others. Perhaps a few bags of Cheetos?
Not so, Fonken says. When looking at the total food intake and total activity, the researchers didn’t see any difference between the groups.
There was a difference, however, when it came to when the mice were eating.
“The ones with the light at night were eating more during their typical rest phase, when they would normally be sleeping,” she says. “They were eating about 55 percent of their food during their rest phase.”
Another experiment was conducted with the same parameters -- light at night or total darkness -- only this time the mice were only allowed to eat within their normal waking period.
The result: skinnier mice. Something about the light changed their feeding behavior and disrupted their metabolism, Fonken suggested.
Fonken and her team haven’t tested their findings out on humans yet, but she says this does have important implications for people.
“If you consume food at the wrong time of day, if you eat during your rest phase, it disrupts your metabolic parameters so you see an increase in weight,” she says.
The Ohio State research backs up prior studies showing that late-night eating influences weight gain. It also helps explain obese people who suffer night eating syndrome – where they obsessively consume calories at night – and seem to experience disruptions in their internal body clocks.
Fonken says this doesn’t mean we should all go to bed as soon as it’s dark out (which in some parts of the country would mean hitting the hay at 4 p.m. in the winter), but we should think about the levels of light we have when we sleep and be cognizant of when we’re eating.
“It could be that ambient levels of light seeping in could make a difference,” she says. “We don’t really know yet, but it might be better for people to have black-out curtains or wear sleep masks. And leave time between their bedtime meal and when they actually go to bed.”