This is the VOA Special English Health Report.

(SOUND)

Loud snoring can be a problem -- and not just for other people trying to sleep with the noise. It can also be a sign of sleep apnea. People with this condition repeatedly stop breathing while they sleep, and may not even know it.

Doctor David Gross is a lung specialist at the National Rehabilitation Hospital of Washington.

DAVIS GROSS: "Sleep apnea means that the airway, the upper airway, cuts off at night. So the person, while he's breathing normally in the daytime, when he goes to sleep, the muscles get all relaxed and cut off and this can happen over and over again, 60 to 100 times an hour."

Most people who snore do not have sleep apnea. But doctors say most people with sleep apnea do snore. Sleep apnea not only reduces sleep quality and makes people feel tired during the day. More and more studies show that it can also lead to strokes and heart attacks.

Dr. Michael Twery of the National Institutes of Health explains why.

MICHAEL TWERY: "Whenever we run out of enough air to breathe, it sends alerting signals to our minds. It raises the level of stress hormones. It tells our heart to work harder."

When a person stops breathing, oxygen levels in the blood decrease. This happens again and again with sleep apnea.

MICHAEL TWERY: "And it's constantly exposing us, night after night, to periods of insufficient oxygen. The level of oxygen in our blood will actually decrease to levels that would be considered a medical emergency."

Dr. Twery compares the effect of sleep apnea to racing a car engine for long periods of time.

MICHAEL TWERY: "Our heart becomes overworked and we become more vulnerable to heart attack."

And also strokes. Dr. Twery led a study of about 9,000 people who had sleep apnea but no history of heart disease. The researchers followed their progress for nine years.

MICHAEL TWERY: "They found that men can experience up to a three-fold increased risk of stroke, and that risk seemed to be well correlated with the severity of sleep apnea."

In other words, the more severe the sleep apnea, the greater the chance of a stroke.

The next step will involve sleep apnea patients who have already had a stroke or heart attack. Researchers will study whether patients can reduce the risk of a second one with a machine called a CPAP. CPAP is continuous positive airway pressure. It provides a continuous flow of air into the throat and lungs while the person sleeps.

Sleep apnea seems to be more common in men than in women, and it becomes more common as people get older. The most common form is called obstructive sleep apnea. People who have it are often overweight or have it in their family, but it can affect anyone. In children, for example, enlarged tonsils in the throat can interfere with breathing as they sleep.

And that's the VOA Special English Health Report. I'm Mario Ritter.

sleep apnea: 睡眠呼吸暫停

tonsil: either of the two small organs at the sides of the throat, near the base of the tongue 扁桃體

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（來源：VOA 編輯：崔旭燕）