It's normal for your muscles to lose tone when you sleep--one reason people in meetings nod off so amusingly. But in 5 to 10 percent of middle-aged and older adults, the throat muscles relax so much that the airway repeatedly closes up--a condition that can be quite deadly, it turns out. According to a study published last week in the New England Journal of Medicine, obstructive sleep apnea sharply elevates the risk of stroke or death.

People with sleep apnea often don't realize they have it, since they don't remember waking up again and again, gasping for breath. Frequently, someone else hears the choking and "industrial-strength snoring," says Klar Yaggi, a sleep specialist at Yale who led the study. He and his colleagues followed two groups of patients who were tested for sleep apnea (defined as stopping breathing five or more times per hour). Some had the condition; some didn't. During the 3 1/2 years or so that they were studied, the people with sleep apnea were about twice as likely to have a stroke or die.

No one really knows why, although the explanation could have to do with the spikes of adrenaline that course through the body when breathing stops, increasing blood pressure, or with repeated plunges in the level of oxygen in the blood. This study didn't look at whether treatment--sleeping with a contraption that blows air into the mouth--lowers the risk. Losing weight can significantly improve sleep apnea, however. And patients who use the machine get more rest, Yaggi says, which should help them avoid another danger of sleep apnea: car accidents.

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