New research suggests that one night of sleep with just a small amount of light may have negative effects on health.
The small, 20-person study conducted by Dr. Phyllis Zee, director of the Center for Circadian (生理节奏的) and Sleep Medicine, was designed to measure the physiological effects of 100 lux (照度) of artificial light on healthy adults while they were sleeping. For the study, all the participants spent their first night sleeping in a mostly dark room. The next night, half of them slept in a better lit room. Meanwhile, the researchers ran tests on the sleepers: brainwaves, heart rates and blood. In the morning, they'd give both groups a large amount of sugar to see how well their systems responded to it.
The group exposed to the light had raised heart rates throughout the night, and also had trouble getting their blood sugar into a normal range.
These changes suggest the small amount of light was enough to shift the nervous system to a more excited and alert state. "It's almost like the brain and the heart knew that the lights were on, although the individual was sleeping," says Zee.
While the findings of this study alone can't predict what would happen in the long term, Dr. Colwell suspects the harmful effects would be cumulative: "This was only one night, so imagine if you' re living that way constantly?"
"That's going to increase the risk of long-term diseases," says Dr. Charles Czeisler whose research has looked at the consequences of circadian rhythm sleep disorder for longer than just one night. He concluded that the unpleasant effects were primarily because of the "internal clock" being disturbed — not necessarily because of the lack of sleep.
This is not to say that the lack of sleep doesn't also have negative effects on health — it does — but he says it simply stresses the lasting consequences of being exposed to light at nighttime.
"People think that as long as they fall asleep and are unconscious, it's not having physiological effects, but that's simply not true," Czeisler says.
