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Even a Small Amount of Light While You Sleep May Harm Your Health

Light exposure while you sleep leads to an elevated heart rate and higher insulin resistance study finds

Enes Evren / Getty Images 4 Stretches to Help You Sleep Better - AARP You’ve probably heard that keeping your bedroom dark can help improve the quality of your sleep. But new research reveals that eliminating artificial light during the night — from a TV set or radio clock or streetlight — could also have a positive impact on your heart and levels. In an , Northwestern University researchers found that adults exposed to even a moderate amount of light while they slept experienced compared to when they slept in a very dark room. They also had more insulin resistance in the morning, which meant their bodies had to work harder to regulate their blood sugar, the study showed. Get instant access to members-only products and hundreds of discounts, a free second membership, and a subscription to AARP the Magazine. Surprisingly, the study subjects who were exposed to the light didn’t report any trouble sleeping. “The upshot is, it appears that light during sleep is affecting you, even if you’re not aware of it,” says study coauthor Phyllis Zee, M.D., director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine. “Your subconscious is aware that there’s light and there’s something going on, and it’s keeping you a little bit on watch. Your fight-or-flight system is more activated.” Elevated heart rate and are risk factors for and early death. The study is important because it highlights a factor you can control that could improve your health and lower your long-term health risk, Zee says.

Effects of light exposure

Previous studies have linked light exposure at night to a variety of health problems, including an increased risk of , type 2 diabetes and some types of cancer. In addition, a large study of 43,722 women published in 2019 found that those who slept with artificial light had a higher risk of gaining weight and being obese than those who slept in a dark room. In light of that research, Zee says she wanted to design a controlled study to examine what happens to your body physiologically when you are exposed to light while you sleep. AARP Membership — $12 for your first year when you sign up for Automatic Renewal Get instant access to members-only products and hundreds of discounts, a free second membership, and a subscription to AARP the Magazine. and a significant increase in their insulin resistance levels compared to the night they slept in a darker environment. Flowers & Gifts 25% off sitewide and 30% off select items See more Flowers & Gifts offers > “What’s new and novel about our work is that it’s giving us a clue about the mechanism — how light exposure during sleep could lead to metabolic disorders,” Zee says.

Eyelids aren t designed to filter out light

Although the study was conducted on young people, Zee says her hunch is that the effect on older adults may be even more prominent. “That’s a population already at risk for insulin resistance,” she says. “It will be very interesting to do these types of studies with older adults because many institutions, like nursing homes, keep the lights on for safety reasons.” Kristin Daley, a psychologist and sleep medicine expert who chairs the clinical practice committee for the Society of Behavioral Sleep Medicine, says the study offers more evidence that it’s best to sleep in complete darkness if possible — a contention she and other sleep clinicians have been making for years. “The problem is, our eyelids are not designed to filter out light,” she says. “We all have receptors in back of our retinas that pick up light even when our eyes are closed.” AARP Membership — $12 for your first year when you sign up for Automatic Renewal Get instant access to members-only products and hundreds of discounts, a free second membership, and a subscription to AARP the Magazine. . If that’s the case, Daley recommends keeping a flashlight on your bedside table and using it to light the way if you visit the bathroom. “It trains the light away from your eye [as opposed to a nightlight, which] direct s the light toward your eye,” she explains. If you prefer to use a nightlight, Zee suggests plugging it in as close to the floor if possible. You may also want to cover it with a red light filter, since studies show red or orange light is less likely than white and blue light to affect brain activity. “I’m not saying you have to sleep in total darkness, because I understand that may not be possible for some people,” Zee says. “The goal is to minimize light exposure and yet create a safe environment.” Michelle Crouch is a contributing writer who has covered health and personal finance for some of the nation’s top consumer publications. Her work has appeared in Reader’s Digest, Real Simple, Prevention, The Washington Post and The New York Times. More on health AARP Membership — $12 for your first year when you sign up for Automatic Renewal Get instant access to members-only products and hundreds of discounts, a free second membership, and a subscription to AARP the Magazine. AARP VALUE & MEMBER BENEFITS See more Health & Wellness offers > See more Flights & Vacation Packages offers > See more Finances offers > See more Health & Wellness offers > SAVE MONEY WITH THESE LIMITED-TIME OFFERS