Study Links Sleep Apnea to Increased Risk of Stroke
Obstructive sleep apnea (OSA) is associated with an increased risk of stroke in middle-aged and older adults, especially men, according to new results from new research supported by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health. Overall, sleep apnea more than doubles the risk of stroke in men.
The research was reported online ahead of the print edition of the American Journal of Respiratory and Critical Care Medicine.
Obstructive sleep apnea is a common disorder in which the upper airway is intermittently narrowed or blocked, disrupting sleep and breathing during sleep. Stroke is the second-leading cause of death worldwide.
The Sleep Heart Health Study (SHHS) is a prospective, multi-center study. Researchers studied stroke risk in 5,422 participants aged 40 years and older without a history of stroke. At the start of the study, participants performed a standard at-home sleep test, which determined whether they had sleep apnea and, if so, the severity of the sleep apnea. Participants were followed for an average of nine years. During that period, a total of 193 participants had a stroke--85 men (of 2,462 men enrolled) and 108 women (out of 2,960 enrolled).
The researchers found that the increased risk of stroke appeared in men with mild sleep apnea and rose with the severity. Men with moderate to severe sleep apnea were nearly three times more likely to have a stroke than men without sleep apnea or with mild sleep apnea. However, in women, the increased risk of stroke was significant only with severe levels of sleep apnea. The increased risk of stroke from sleep apnea is independent of other risk factors such as weight, high blood pressure, race, smoking, and diabetes.
The researchers suggest that the differences between men and women might be because men are more likely to develop sleep apnea at younger ages. Therefore, they tend to have untreated sleep apnea for longer periods of time than women.
"It's possible that the stroke risk is related to cumulative effects of sleep apnea adversely influencing health over many years," noted Susan Redline, M.D., MPH, professor of medicine, pediatrics, and epidemiology and biostatistics, at Case Western Reserve University in Cleveland and lead author of the paper.
"Research on the effects of sleep apnea not only increases our understanding of how lapses of breathing during sleep affects our health and well being, but it can also provide important insight into how cardiovascular problems such as stroke and high blood pressure develop," said Michael J. Twery, Ph.D., director of the NIH National Center on Sleep Disorders Research, an office administered by the NHLBI.
The new results support earlier findings that have linked sleep apnea to stroke risk. SHHS researchers have also reported that untreated sleep apnea is associated with an increased risk of high blood pressure, heart attack, irregular heartbeats, heart failure, and death from any cause. Other studies have also linked untreated sleep apnea with overweight and obesity and diabetes. It is also linked to excessive daytime sleepiness, which lowers performance in the workplace and at school, and increases the risk of injuries and death from drowsy driving and other accidents.
"Our findings provide compelling evidence that obstructive sleep apnea is a risk factor for stroke, especially in men," Redline said. "Overall, the increased risk of stroke in men with sleep apnea is comparable to adding 10 years to a man's age. Importantly, we found that increased stroke risk in men occurs even with relatively mild levels of sleep apnea.
"We now have abundant evidence that sleep apnea is associated with cardiovascular risk factors and diseases. The next logical step is to determine if treating sleep apnea can lower a person’s risk of these leading killers," Redline added. "Our research group is now developing the additional research and resources to begin answering this important question."
John Heffner, M.D., past president of the ATS emphasized the importance of this study. "We now have strong evidence from this study that obstructive sleep apnea increases stroke risk directly. But we also have emerging evidence from other studies that sleep apnea may further increase stroke risk by causing, or at least accelerating, other diseases, such as diabetes, that contribute to cerebrovascular disease," he said. "The importance of diagnosing and treating obstructive sleep apnea requires greater emphasis in general clinical practice considering it is still under-recognized by primary care physicians."