sleep-w-iStock

An estimated one in four men has sleep-disordered breathing. ((iStock))

Severe sleep apnea can increase the risk of premature death compared with people without the sleep disorder, U.S. researchers say.

In particular, men aged 40 to 70 with severe sleep-disordered breathing were twice as likely to die from any cause as healthy men the same age without the condition over the eight years of follow-up, Naresh Punjabi of Johns Hopkins University in Baltimore and his colleagues reported in Tuesday's issue of Public Library of Science journal PLoS Medicine.

The researchers studied more than 6,000 men and women aged 40 and older. None of them were being treated for sleep-disordered breathing when the study began.

In sleep-disordered breathing, the upper airway collapses during sleep. About one in 10 women and one in four men have the chronic condition, although most are unaware of their problem, according to the researchers.

The team assessed participants' nighttime breathing, sleep patterns and blood oxygen levels to calculate the number of sleep apneas — brief interruptions of breathing that can last from a few seconds to more than a minute.

Previous studies showed sleep apnea can lead to increased incidence of hypertension, heart failure and stroke as well as daytime sleepiness, which can interfere with the ability to drive a car or operate machinery. But earlier studies did not include enough participants to show whether factors such as age or gender are linked to an increased risk of premature death.

During the follow-up period of the latest study, 1,047 participants (587 men and 460 women) died.

Apnea lowers blood oxygen

Regardless of age, sex, race, weight or smoking status, participants were 1.5 times more likely to die during the average eight-years of follow-up if their blood showed apnea-induced low blood oxygen when the study began, the researchers found. They measured the number of times per hour that subjects' breathing slowed or became shallow — which correlated with low blood oxygen.

Among men in the study, 42.9 per cent did not have sleep-disordered breathing, 33.2 per cent had mild disease, 15.7 per cent had moderate disease, and 8.2 per cent had severe disease.

In women, 63.7 per cent did not have the condition, 24.5 per cent had a mild form, 7.9 per cent moderate and 3.0 had severely disordered breathing.

People with milder sleep-related breathing problems did not show a statistically increased risk of premature death in the study.

Death from coronary artery disease was also linked with sleep-disordered breathing in men but not women.

Mortality predictor

"In conclusion, the Sleep Heart Health Study shows that sleep-disordered breathing is an independent predictor of mortality and that this association is not attributable to age, obesity, or other chronic medical conditions," the study's authors wrote.

Given the high prevalence of sleep-disordered breathing in the general population, the researchers and journal editors called for more research to assess if treatment can reduce premature mortality associated with the disorder.

A limitation of the study is that it relied on a single night's measurements to diagnosis sleep-disordered breathing.

The study was funded by the National Heart, Lung, and Blood Institute. Several authors reported receiving support from companies that produce diagnostic tools and treatments for sleep-disordered breathing.