Scientists from the National Center on Sleep Disorders Research reported Friday that people with severe sleep apnea, also known as sleep-disordered breathing, are many times more likely to die from any cause than those without the condition.
The 18-year study confirmed previous, smaller studies suggesting an increased risk of death for people with the disorder.
“This is not a condition that kills you acutely. It is a condition that erodes your health over time,” Dr. Michael J. Twery, director of the National Center on Sleep Disorders Research, told the Associated Press. The center is part of the National Heart, Lung and Blood Institute, which is under the U.S. National Institutes of Health.
People with these conditions “have been sleep deprived for perhaps very long periods of time, they are struggling to sleep. If this is happening night after night, week after week, on top of all our other schedules, this is a dangerous recipe,” Twery said.
According to estimates from the institute, 12 million to 18 million people in the U.S. have moderate to severe apnea. Since victims are asleep when the problem occurs, the condition is not easily detected. In the current study, researchers initially tested participants for sleep-disordered breathing in the laboratory and then followed them over the next several years.
For those with apnea, their upper airway becomes periodically narrowed or blocked during sleep, preventing air from reaching the lungs. In some cases, breathing may cease altogether for up to a minute. These pauses in breathing disrupt sleep and prevent sufficient oxygen from reaching the bloodstream.
“When you stop breathing in your sleep you don’t know it, it doesn’t typically wake you up,” said Twery.
Instead, it often causes a person to move from a state of deep sleep to light sleep, when breathing resumes. This can happen hundreds of times per night, disrupting overall sleeping patterns.
Twery said that a person will usually have four or five nightly cycles of light sleep, deep sleep and REM (rapid eye movement) sleep, the cycle in which most dreams occur. Typically, more deep sleep happens early in the night, whereas more REM sleep occurs closer to waking. This pattern serves to control metabolism, hormones and stress levels. The institute has linked apnea to an increased risk of high blood pressure, heart disease, stroke, diabetes and excessive daytime sleepiness.
In the current study, led by Terry Young of the University of Wisconsin, Madison, Wisconsin Sleep Cohort followed 1,522 adults ages 30 to 60, and found the annual death rate in those without sleep apnea was 2.85 per 1,000 people per year. However, for those with mild and moderate apnea the death rates were 5.54 and 5.42 per 1,000, respectively, while those with severe apnea had a rate of 14.6, researchers reported.
Furthermore, while cardiovascular mortality accounted for 26 percent of deaths among those without apnea, it accounted for 42 percent of the deaths among those with severe apnea, according to researchers.
A separate Australian study involving 380 adults aged 40 to 65 reached a similar conclusion. The study found that after 14 years, nearly one in three participants with moderate to severe sleep apnea had died, compared with only 6.5 percent of those with mild apnea and 7.7 percent of those without the disorder.
“Our findings, along with those from the Wisconsin Cohort, remove any reasonable doubt that sleep apnea is a fatal disease,” Dr. Nathaniel Marshall of the Woolcock Institute of Medical Research, the study’s lead author, told the Associated Press.
Sleep apnea is often treated with a special mask-like device placed over the nose and/or mouth that delivers continuous positive airway pressure. The National Center on Sleep Disorders study found reduced death rates in patients using the device. The report referenced debate over the use of airway pressure to treat patients who are not lethargic during the day.
According to the U.S. researchers, 95 percent of the participants in their study were white, with adequate health care access and income.
“It is likely that our findings may underestimate the mortality risk of SDB in other ethnic groups or the lowest socio-economic strata where there is poor awareness and access to health care,” they wrote in their report.
The U.S. National Institutes of Health supported the U.S. research, while the Australian study was funded by the Australian National Health and Medical Research Council.
Both studies were published in Friday’s edition of the journal Sleep. Abstracts of the studies can be viewed at http://www.journalsleep.org/ViewAbstract.aspx?citationid=3621 and http://www.journalsleep.org/ViewAbstract.aspx?citationid=3622.
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