"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, diabetes and metabolic syndrome," says Phyllis Zee, MD, PhD, chief of Sleep Medicine in The Ken and Ruth Davee Department of Neurology at Northwestern University Feinberg School of Medicine, a Northwestern Medicine physician and senior author of the study. "It's important for people to avoid or minimize the amount of light exposure during sleep."

Here are some ways to reduce light exposure:  

• Don't keep lights on when you're sleeping. If you need to have a light on for safety, use a dim light that is closer to the floor.
• Color is important. If you must have a light on, choose an amber, red or orange light, which is less stimulating for the brain. Don't use white or blue light. And, keep it as far away from you as possible while you're sleeping.
• Shield yourself from outside light. Use blackout shades or eye masks if you can't keep light out of the room. Move your bed so outdoor light isn't shining on your face.

There is evidence that light exposure during daytime activates the autonomic nervous system, which controls your body's involuntary activities. This increases your heart rate and heightens your alertness to meet the challenges of the day.

"We showed your heart rate increases when you sleep in a moderately lit room," says Daniela Grimaldi, MD, PhD, co-first author of the study and a research assistant professor of Neurology in the Division of Sleep Medicine at Northwestern Medicine. "Even though you are asleep, your autonomic nervous system is activated. That's bad. Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day."