If you spend your evenings on the couch flipping through channels or staying up late to boost your high score on the latest shoot-em-up video game, you probably already know your risk for obesity is a touch on the high side.

What you didn’t know is all that time spent holding down the couch may not be the only reason why.

According to researchers from the Ohio State University and the University of Haifa, the problem isn’t just being sedentary but being exposed to too much light at night.

People are programmed to have a certain number of light and dark hours each day. Everyone has an internal body clock called a circadian rhythm. Staying up late in a room illuminated by hazy glow of the television can throw this clock out of balance.

As part of the study, the scientists watched what happened to groups of mice who were exposed to different levels of light during the day. The mice were broken up into three groups. One set was exposed to a typical schedule with eight hours of total darkness each day. The second group got eight hours of dim light, so not total darkness but not full light either. The third lived in full light all day. Although the mice all ate the same chow and exercised, the mice who had eight hours of darkness every day ended up weighing less than the other mice and ate a smaller percentage of their food.

Other problems can result when your circadian rhythm goes rogue, namely problems with sleep. Interestingly, numerous studies have linked not getting enough Z’s at night to an increased risk for obesity as well.

Word to the wise? It may be your best bet to try to turn off the TV, get to bed a little earlier, and get in a few more winks.

After all, who doesn’t want a little more sleep?