A recent Ohio State U. study found that eight weeks of exposure to light at night caused mice to gain nearly 50 percent more weight than mice given eight hours of darkness daily.
Laura Fonken, a doctoral student in neuroscience, and Randy Nelson, a professor of neuroscience and psychology, began the study examining human evidence, such as the increased body mass index among night-shift workers, Fonken said.
“There’s been some evidence in studies with humans that kind of led us to be interested in this question, and not a lot of people have looked at these effects,” Fonken said.
Nelson said there is also a possible link to weight gain for college students.
“Perhaps part of the ‘freshman 15′ represents a shift to a more nocturnal lifestyle in college,” Fonken said.
However, results are not conclusive for humans, Fonken said.
“It’s very hard to say at this point whether or not we will find a similar pattern in humans, just because we haven’t looked yet, but it might start to explain some of the mechanisms we need to further investigate before drawing conclusions,” she said.
The study placed some mice in a standard light-dark cycle, with 16 hours of light and eight hours of darkness.
The others lived in a light-dim cycle, with 16 hours of light and eight hours at 5 lux of light, the equivalent of an open computer screen.
After one week, the mice with light at night gained more weight than the others and continued to gain weight during the eight-week study. There reasons for the weight gain wasn’t clear at first, Fonken said.
“We thought there was probably a difference in activity and how much food was consumed over a day, but both were the same,” Fonken said.
The weight gain could be caused by abnormal eating patterns among mice in the light-dim cycle, researchers said. They concluded that the mice in that cycle consumed more food at abnormal times, causing an increase in weight.
A follow-up study limiting food to the time of day when mice were most active led to the same amount of weight gain for both groups of mice.
“I think that by showing the increased fat could be blocked simply by restricting food intake to the active part of the day (night in the case of these nocturnal creatures) indicates a shift in metabolism and likely biological clock genes,” Nelson said in an e-mail.
Light at night does not affect corticosterone, a stress hormone that influences metabolism, but it might cause problems with melatonin, another hormone correlated with metabolism, Fonken said.
Research also showed that the mice exposed to light at night had a reduced glucose tolerance, an indication of a pre-diabetic state, she said.
According to the Centers for Disease Control and Prevention’s website, diabetes is directly linked to being obesity. The CDC predicted one in three Americans will have diabetes by 2050.
Aarthi Gobinath, a third-year in microbiology and Spanish, said she is surprised that something as seemingly harmless as light at night might be related to obesity and diabetes.
“I think it is definitely important to study,” she said. “Obesity is kind of an epidemic these days in developed countries, and anything that can be done to change the current habits is great.”
Nelson agreed that research is an important step toward improving quality of life.
“Obesity is associated with poor quality of life and reduced longevity,” he said. “It is growing in prevalence across the world, and no one really understands why that is so, especially in places where diets have not changed substantially over the past few years.”
Fonken said researchers will continue to build on the study.
“The most exciting result is that exposure to such low levels of light can have such an impact on body weight without changing the number of calories ingested or the amount of activity shown by the individual,” Nelson said. “We are interested in following up to look at the inflammatory effects of light at night in both brain and fat tissue.”