Blogs-14 Reducing Ambient Light During Sleep Improves Health

Moonlight gently wafting through the window at night may be somewhat romantic and soothing, but the darker your room when you sleep, the healthier you may become, according to researchers who state that even moderate light exposure during sleep can harm your heart and also increase insulin resistance.

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 study. 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.

"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. "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.

Co-author Dr. Daniela Grimaldi commented, "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.

The researchers 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 commented. "We show it's affecting your ability to regulate glucose."

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. A significant proportion of individuals (up to 40%) sleep with a bedside lamp on or with a light on in the bedroom and/or keep the television on.

The study tested the effect of sleeping with 100 lux (moderate light) compared to 3 lux (dim light) in participants over a single night. The investigators discovered that moderate light exposure caused the body to go into a higher alert state. In this state, the heart rate increases as well as the force with which the heart contracts and the rate of how fast the blood is conducted to your 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 said.

Citation:

Mason IC, et al. “Light exposure during sleep impairs cardiometabolic function.” Proceedings of the National Academy of Sciences, 2022; 119 (12)