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Leaving the light on hampers sleep quality: study

By Kathryn Doyle

NEW YORK (Reuters Health) - Falling asleep in the glow of the TV or leaving a light on next to the bed can affect brain activity levels and lead to poor quality sleep, according to the authors of a new study.

"Our study showed that even a low light interferes with good sleep by inducing more light sleep, less deep sleep and more frequent micro-arousals during sleep," which is a new finding, Dr. Seung-Bong Hong said.

Hong, from the Samsung Medical Center of Sungkyunkwan University School of Medicine in Seoul, South Korea, is the senior author of the report.

The researchers had 10 healthy people sleep for two nights while machines assessed changes in their heart rate, breathing and brain and muscle activity.

The first night, there was no artificial light in the room.

On the second night, a fluorescent lamp was placed a few feet from the sleeping subject.

The total amount of time people spent in bed and the time they spent sleeping were similar whether the light was on or off.

But with the light on, sleepers spent more time in stage 1 sleep - the shallowest kind - and less time in stage 3 and 4 sleep.

That's similar to what happens to people with sleep apnea, Hong said.

Higher sleep stages are important for memory, he added.

Nine out of the 10 sleepers reported feeling like they got poorer quality sleep when the light was on, according to results published in Sleep Medicine.

With the light on, the researchers also recorded more "micro-arousals" - periods when the brain appears to be near-awake for more than three seconds.

"Chronic poor quality of sleep is detrimental both to mental and physical function and to health," Hong told Reuters Health in an email.

The study did not look at any possible health consequences of sleeping with a light on.

"What's truly surprising is that this kind of study hasn't been done before," Michael Gorman said.

Gorman is a biopsychologist who studies circadian rhythms at the University of California, San Diego. He was not involved in the new study.

"We know light at night increases alertness when awake, but I reviewed this literature a few years ago and was stunned to find out that no one had ever compared sleep in dark versus light in humans," Gorman told Reuters Health.

Ten people constitutes a fairly small study, he cautioned, and the fluorescent light the researchers used is relatively strong.

"It's not like the light from your alarm clock," he said. "People don't need to go out and get blackout curtains."

Humans spend one-third of their lives sleeping, Gorman said, and researchers still know very little about what altering this aspect of life does to a person.

Stage 1 sleep did seem to be affected by light, which is intriguing and requires more study, he said. But it's also important to note that although people say it's harder to sleep with a light on, they fall asleep pretty well in many conditions, he added.

No one should change the way they sleep based on this study, which is very preliminary, Gorman said.

"People can experiment with their sleep and see what works better, though," he said. "They're not going to do any harm."

SOURCE: http://bit.ly/1bug433 Sleep Medicine, online November 8, 2013.

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