Sleeping with a dim light like a television or nightlight is enough to the raise blood sugar and heart rates of healthy people, according to a new study. Light helps our body maintain an internal clock, but artificial light at night can interrupt the rest and repair that should happen during the sleep. New research suggests that even when our eyes are closed, a small amount of light can disrupt the way our bodies normally keep our blood sugar within a healthy range.
In the study published in Sciences on Monday, scientists asked 20 participants ages 19 to 36 to spend two nights in their lab. On the first night of sleep, the volunteers slept in a very dark room. For their second night of sleep, half of the group snoozed with a small light like the glow of television at night, or streetlights through a window—and half spent their second night in a dark room.
During the trial, all participants were connected to devices that measured different markers of their sleep quality. They were each connected via a special tube, allowing researchers to collect samples without waking the individual. Researchers also recorded participants' heart rates and brain waves.
When the volunteers awoke in the morning, the team tested their blood sugar and found that participants that slept in rooms with a dim light spent less time in deep sleep. In addition to having slightly worse blood sugar control, the group exposed to dim light had a higher heart rate on average. "By comparison, those that spend two nights in the dark room had little difference in their blood sugar control. They thought they slept well, but your brain knows that the lights are on," says Zee, "you should clearly pay attention to the light in your bedroom. If you can't give up your night light, keep it dim and at floor level."
Earlier work has linked exposure to light during sleep to an increased risk of obesity in women. Zee recommends, "make sure that you start dimming your lights at least an hour or two before you go to bed to prepare your environment for sleep."
