EVANSTON, Ill. — Closing your curtains won’t just give you more privacy at night, a new study finds it can also protect your heart while you sleep! Researchers from Northwestern University found that even a small amount of light exposure while sleeping increases the risk of heart disease and diabetes.
Researchers say heart rates rise and the body can’t rest properly when there’s light in a bedroom. Their findings add that exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, harms cardiovascular function and increases insulin resistance the following morning.
“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 senior study author Dr. Phyllis Zee in a university release. “It’s important for people to avoid or minimize the amount of light exposure during sleep.”
Zee says there is already evidence that light exposure during daytime increases heart rate through the activation of the sympathetic nervous system, which kicks the heart into high gear and heightens alertness to meet the challenges of the day.
“Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep,” Dr. Zee continues.
“We showed your heart rate increases when you sleep in a moderately lit room,” adds co-first author Dr. Daniela Grimaldi, an assistant professor of neurology at Northwestern. “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.”
Your brain senses light even while you sleep
Researchers explain that there are sympathetic and parasympathetic nervous systems to regulate our physiology during the day and night. The sympathetic system takes charge during the day while the parasympathetic works at night, when it conveys restorative benefits to the entire body.
Study authors found that insulin resistance occurred the morning after people slept in a lit room. Insulin resistance occurs when cells in muscles, fat, and the liver don’t respond well to insulin and can’t use glucose from blood for energy. To make up for it, the pancreas makes more insulin. Over time, blood sugar goes up.
Dr. Zee says that an earlier study looked at a large group of healthy people who had exposure to light during sleep. They were more overweight and obese.
“Now we are showing a mechanism that might be fundamental to explain why this happens. We show it’s affecting your ability to regulate glucose,” Zee says.
The participants in the study weren’t aware of the biological changes in their bodies at night.
“But the brain senses it,” Grimaldi explains. “It acts like the brain of somebody whose sleep is light and fragmented. The sleep physiology is not resting the way it’s supposed to.”
How can you cut down on nighttime light?
The team adds that exposure to artificial light at night during sleep is common, either from indoor light emitting devices or from sources outside the home, particularly in large urban areas. Up to four in 10 people sleep with a bedside lamp on or with some other light or television on in the bedroom.
“In addition to sleep, nutrition and exercise, light exposure during the daytime is an important factor for health, but during the night we show that even modest intensity of light can impair measures of heart and endocrine health,” says co-first author Dr. Ivy Mason, who is now a research fellow at Harvard Medical School.
The study tested the effect of sleeping with 100 lux (moderate light) compared to three lux (dim light) in participants over a single night. The team discovered that moderate light exposure caused the body to go into a higher alert state. In that state, the heart rate increases as well as the force with which the heart contracts and the rate of how fast the blood travels to blood vessels for oxygenated blood flow.
“These findings are important particularly for those living in modern societies where exposure to indoor and outdoor nighttime light is increasingly widespread,” Zee concludes. “If you’re able to see things really well, it’s probably too light.”
Researchers have three top tips for reducing light during sleep:
- Don’t turn lights on. If you need to have a light on, which older adults may want for safety, make it a dim light that is closer to the floor.
- Color is important. Amber or a red/orange light is less stimulating for the brain. Don’t use white or blue light and keep it far away from the sleeping person.
- Blackout shades or eye masks are good if you can’t control the outdoor light. Move your bed so the outdoor light isn’t shining on your face.
The findings are published in the journal Proceedings of the National Academy of Sciences.
South West News Service writer Stephen Beech contributed to this report.