Close the blinds, draw the curtains, and turn off all the lights before bed. Exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, harms your cardiovascular function during sleep, and increases your insulin resistance the following morning, reports a new Northwestern Medicine study.
“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,” said senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “It’s important for people to avoid or minimize the amount of light exposure during sleep.”
There is already evidence that light exposure during daytime increases heart rate via activation of the sympathetic nervous system, which kicks your 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,” Zee said.
Added Dr. Daniela Grimaldi, co-first author and research assistant professor of neurology at Northwestern: “We showed your heart rate increases when you sleep in a moderately lit room. 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.”
There are sympathetic and parasympathetic nervous systems to regulate our physiology during the day and night. Sympathetic takes charge during the day, and parasympathetic is supposed to at night, when it conveys restoration to the entire body.
Investigators found insulin resistance occurred the morning after people slept in a light room. Insulin resistance is when cells in your muscles, fat, and liver don’t respond well to insulin and can’t use glucose from your blood for energy. To make up for it, your pancreas makes more insulin. Over time, your blood sugar goes up.
An earlier study published in JAMA Internal Medicine looked at a large population of healthy people who had exposure to light during sleep. They were more overweight and obese, Zee said.
“Now we are showing a mechanism that might be fundamental to explain why this happens,” Zee said. “We show it’s affecting your ability to regulate glucose.”
The participants in the study weren’t aware of the biological changes in their bodies at night.
“But the brain senses it,” Grimaldi said. “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.”