New research from scientists at Northwestern Medicine presents a persuasive argument for people to get rid of nightlights and break the common habit of being lulled to sleep by a television program.

Why should we sleep in the dark?

According to a press release about the study, even a small amount of light can affect your cardiovascular function as you sleep, resulting in increased insulin resistance when you wake up. What does that mean? Well, the light exposure can end up raising your risk for higher blood pressure and even diabetes.

“The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, disobeys, and metabolic syndrome,” explains Dr. Phyllis Zee, chief of sleep medicine at the Northwestern University School of Medicine and lead author of a study about the research.

Usually, your heart rate drops at night while sleeping, and rises again in the morning when we are exposed to sunlight, activating our sympathetic nervous system. However, even just a dim glow can have the same effect on us during our sleeping hours.

In the release mentioned above, Dr. Daniela Grimaldi, research assistant professor of neurology at Northwestern and co-author of the study, explains this further. “Even though you are asleep, your automatic nervous system is activated. That’s bad,” she says. “Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day.”

What should we do about it?

The next time you hit the sack, make sure to turn off all the lights—yes, that means putting your phone away and turning off whatever you’re streaming. Draw your curtains or shut your blinds if street lights creep in through your window, or alternatively, if you don’t have effective window coverings, then think about investing in a sleep mask.