Sleeping with even a small amount of light in the room can harm the heart and increase blood insulin levels, according to researchers. The study underscores the importance of avoiding or minimizing light exposure during sleep, they said.
Exposure to artificial light at night is common in large urban areas, where many people sleep with a bedside lamp, keep a light on in the bedroom, or keep the television on. Past studies have implicated ambient nighttime light exposure as a risk factor for adverse health outcomes, including cardiometabolic heart disease. But the exact effects of light exposure during sleep on cardiometabolic health and the associated mechanisms behind it are unclear.
In the new study, researchers studied 20 healthy people in their 20s and had them spend two nights in a sleep lab. One group of 10 slept in dimly lit conditions for two consecutive nights, while the other group of 10 slept in dimly lit conditions for only one night followed by one night of sleep under much brighter conditions with overhead room lighting. Researchers measured the insulin levels and heart rates of the participants during the study. Those who were exposed to the brighter room light conditions developed a higher heart rate and increased insulin resistance the next morning. The researchers believe that exposure to more light during sleep can impair glucose metabolism, possibly through increase activation of the sympathetic nervous system.
The study, funded in part by the NHLBI, appeared in Proceedings of the National Academy of Sciences.