To get a good night’s sleep, turn off the lights. However, in our constantly illuminated world, many people disregard this advice. Researchers are attempting to gain a better understanding of how nighttime light can harm our health.

Perhaps it’s falling asleep in front of the TV, the collective glow of electronics, or an obtrusive streetlight outside the window. Light pollution infiltrates our nighttime hours in a variety of ways, and research indicates that it is harmful to our health, particularly our metabolic health. So, what would the consequences be after only one night’s sleep?

Light’s Physiological Effects

“This is about enough light to see your way around, but it’s not enough light to read comfortably,” Zee says. For the study, all participants slept in a mostly dark room on the first night. The next night, half of them slept in a brighter room (the light was placed overhead).

Meanwhile, the researchers conducted tests on the sleepers, including recording brainwaves, measuring heart rates, and drawing blood every few hours, among other things. They’d give both groups a large dose of sugar in the morning to see how their systems reacted to the spike.

Light can interfere with metabolism

Although having the light on disrupts sleep quality, this study did not find that result while monitoring the people in the lighted room. In fact, the majority of the participants reported that they had a good night’s sleep.

Melatonin levels were also measured by the researchers, a hormone that aids in the timing of circadian rhythms and promotes sleep. Melatonin is normally suppressed during the day and increased at night.

According to studies, artificial light at night can suppress melatonin levels, and scientists have discovered a link between melatonin disruption and several diseases, including cancer and diabetes. However, the study found no evidence that melatonin levels were lower in people who slept with the light on.

Chronic illness risk is increased

Some of these human studies used much brighter light intensities — and not while people were sleeping. While the findings of this study cannot predict what will happen in the long run, Colwell believes the negative effects will be cumulative: “This was only one night, so imagine if you’re living that way all the time?”

The body’s “master clock,” called the suprachiasmatic nucleus, is found in the brain, but organs and tissues throughout the body have their own cellular timekeeping devices. Insulin-secreting cells in the pancreas are one example. Disrupting the sleep-wake cycle can affect their ability to appropriately secrete insulin, which in turn controls blood sugar.