Study shows light during nighttime sleep bad for heart health, insulin absorption, weight

Lullabye, and goodnight, make sure you turn out the light.

That’s the message emanating from results of a new study that illuminates the effect of even a small amount of overnight light on the body’s insulin absorption capabilities, and thus heart health.

A good 40% of people sleep with some kind of light, be it a bedside lamp or the television. But even one night of that can launch a domino effect in even the healthiest of people, a new study indicates.

The light dampens cardiovascular function during sleep, which in turn leads to insulin resistance the next morning – which can mark a roadmap to diabetes. Insulin-resistant cells are unable to extract glucose from the blood to make energy for bodily functioning. In response, the pancreas ups its insulin production. Eventually, this process increases blood sugar levels, which can lead to diabetes.

It didn’t take much ambient lighting during nighttime sleep to jump-start this reaction, researchers at Northwestern University Medicine found.

“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, in a statement. “It’s important for people to avoid or minimize the amount of light exposure during sleep.”

Plenty of evidence already existed to show that exposure to light during the daytime activates the sympathetic nervous system to increase the heart rate, which is necessary for charging through the day, the researchers explained.

This study, published Monday in Proceedings of the National Academy of Sciences (PNAS), the official journal of the National Academy of Sciences, looked at the effects of that light response at night.

“Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep,” Zee said.

“We showed your heart rate increases when you sleep in a moderately lit room,” said Dr. Daniela Grimaldi, a co-first author and research 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.”

Previous studies had found that people exposed to light during sleep tended to be more overweight and obese, Zee said in the statement. The new study gave an indication as to why.

The team studied 20 healthy people in their 20s and set them up with sleep monitors to spend two nights in a sleep lab, one night in a dark room. The second night, some of them were put under dim overhead light. Vital signs were measured throughout.

Those exposed to light had a higher heart rate, insulin resistance and their nervous systems were out of whack, a factor linked to higher blood pressure, as CNN noted.

While the study was small, the results pointed to the need for further research and corroborated previous findings, scientists not involved in it said.

“Light is the strongest signal to our circadian pacemaker that controls rhythms in physiology and behaviour, including in metabolism,” Jonathan Cedernaes, a professor at Uppsala University in Sweden, told The Guardian.

To ensure a healthy night’s sleep, the researchers suggest that people turn off all the lights, or have a dim one near the floor; eschew white or blue light, and keep that far from the person who’s sleeping; use blackout shades or masks to keep outdoor light at bay.

“Light is the strongest signal to our circadian pacemaker that controls rhythms in physiology and behaviour, including in metabolism,” Jonathan Cedernaes, a professor at Uppsala University in Sweden, told The Guardian.