'This is probably the best data available now showing that if you have obstructive sleep apnea, you have an increased risk for stroke or death.'

The study of nearly 700 people found a doubled risk of stroke in all those with sleep apnea, and a threefold increased risk in those with a severe case of the condition.

"We followed people with sleep apnea forward in time to see who had strokes or died, and found this increased risk," said lead researcher Dr. H. Klar Yaggi, an assistant professor of medicine at the Yale University School of Medicine. "What our study found is a new risk factor for the development of stroke."

His team published its findings in the Nov. 10 issue of the New England Journal of Medicine.

Chicken-or-Egg Question

Other studies looking at sleep apnea and stroke have been done, but they focused on the incidence of sleep apnea in people who had already suffered strokes, Yaggi explained.

Those studies found that "a high percentage of patients with stroke have sleep apnea," he said. But they didn't solve the chicken-or-egg question of whether sleep apnea helps trigger stroke, or whether stroke risk factors cause sleep apnea by affecting the brain's sleep center.

But in its three-year prospective study, Yaggi's team found that the presence of sleep apnea nearly doubled the risk of stroke or death, even after the researchers adjusted for other risk factors.

The finding closes a gap in knowledge about the relationship between sleep apnea and heart problems, said Dr. Virend K. Somers, a professor of medicine at the Mayo Clinic, who wrote an accompanying editorial.

"We know there is an association between obstructive sleep apnea and various kinds of heart disease -- hypertension, atrial fibrillation, stroke and heart failure," he said. "We've never been able to prove that sleep apnea causes these things, other than hypertension. The evidence has been mainly circumstantial, and that is especially true of people with stroke. This is probably the best data available now showing that if you have obstructive sleep apnea, you have an increased risk for stroke or death."

Missing Piece

But there is still one more missing piece to the puzzle, Yaggi said.

"The next research has to be on the impact of treating sleep apnea," he said. "The question that this study raises is whether primary or secondary prevention would be helpful in reducing the risk."

No such trials are now underway, said Dr. Carl E. Hunt, director of the National Center on Sleep Disorders Research at the National Heart, Lung, and Blood Institute (NHLBI), which helped finance Yaggi's trial.

NHLBI is funding two trials on the effectiveness of the current first-line medical treatment for sleep apnea, continuous positive airway pressure (CPAP), Hunt said, "but neither of these clinical trials addresses stroke as a primary outcome."

However, the newly reported trial "provides a very rational basis for undertaking long-term interventional trials," he said.

Weight Loss

Another paper in the same issue of the journal reported that CPAP did not help people with a variant of the condition called central sleep apnea. But Yaggi noted that this form has a different cause than obstructive sleep apnea.

"Central sleep apnea is much less common, and results from a problem with the brain's breathing center, so that there is a lack of drive to breathe," he said. "Obstructive sleep apnea, which is significantly more common, is a problem of the upper airway, which is all muscle. When people with obstructive sleep apnea are awake and alert, there is enough muscle to keep the airway open. During sleep, they lose tone. The airway becomes significantly relaxed and closes off. The result is what I call 'industrial-strength' snoring."

Daytime drowsiness is another sleep apnea side effect, Somers said. "Until now, physicians have worked against sleep apnea primarily to prevent daytime sleepiness," he said. "We still need to prove that it can prevent stroke, but we believe that treating sleep apnea is good for a patient's heart disease."

Weight loss is perhaps the most direct intervention in fighting sleep apnea, since the condition often is associated with obesity, Yaggi added. "Weight loss of 10 to 20 percent can significantly reduce sleep apnea," he said.

More information: Find out more on sleep apnea at the National Library of Medicine.