MADISON - A continuing study of sleep problems in the general population shows some alarming findings: over an 18-year period, people with severe, untreated sleep apnea died a rate more than three times that of those without apnea.
Sleep apnea, a condition of repeated episodes of breathing pauses during sleep, is measured by the number of complete or partial halts in breathing per hour of sleep. In a paper published in the August issue of SLEEP, researchers found that the higher the number of breathing pauses, the greater the risk of death.
The conclusion comes from a study led by University of Wisconsin-Madison epidemiologist Terry Young, PhD, of the School of Medicine and Public Health.
"We have been studying the effects of sleep apnea in the Wisconsin Sleep Cohort for more than a decade and have reported links between sleep apnea and hypertension, stroke and depression," said Young, a professor in the department of population health sciences at UW-Madison.
"However, our new findings of a strong and significant decrease in survival with severe, untreated sleep apnea show most dramatically the serious health risk sleep apnea poses."
In addition, Young and her co-authors found the risk of cardiovascular death was strikingly high for participants with severe sleep apnea who had not reported being treated for it. People who had 30 or more breathing pauses per hour of sleep, compared to those who had fewer than five, had five times the risk of cardiovascular death over the 18-year period.
The good news is that people who reported that they had used continuous positive air pressure therapy (CPAP) for their sleep apnea fared better. After the participants who had reported CPAP treatment were excluded from the analysis, the cardiovascular mortality risk jumped from a three-fold risk to a five-fold increase in death.
Young is principal investigator of the Wisconsin Sleep Cohort Study, a longitudinal, community-based epidemiology study of sleep apnea and other sleep problems. The study, begun in 1989, is based on a random sample of 1,522 Wisconsin state employees. The participants undergo overnight sleep studies that include polysomnography – an all-night recording of sleep and breathing – and many other tests at four-year intervals. The studies are conducted in a specially designed unit at the federally funded UW Institute for Clinical and Transitional Research Center (ICTR).
Based on the results from participants' first polysomnography studies, Young found that 63 people (or four percent of the group) had severe sleep apnea, 20 percent had mild or moderate sleep apnea, and 76 percent had no sleep apnea.
In March 2008, researchers examined state death records and found that about 19 percent of participants with severe sleep apnea had died (12 deaths), compared with about four percent of participants with no sleep apnea (46 deaths).
Participants in the study were not selected because they were patients with known sleep problems. After the testing, researchers contacted participants with severe sleep apnea, and explained the condition, its health risks, and recommended seeing their doctor. Despite this information, most failed to seek diagnosis or treatment for their apnea. Furthermore, their primary care doctors may have been unaware of the need for further evaluation of reports of loud, irregular snoring and breathing pauses.
While intervention and treatment for sleep apnea was not part of this study, it is offered at an increasing number of health facilities in the U.S. In Madison, treatment is available at Wisconsin Sleep, located in the University Research Park. Young’s report in the journal, SLEEP, underscores the need for diagnosis of sleep apnea.
"I think many people who wrote off their snoring or apnea as a minor problem will be stunned by these findings, as the sleep-research community is," said Dr. Ruth Benca, medical director of the Wisconsin Sleep Clinic.
"The silver lining is that treatment for sleep apnea seems to help decrease the risk of death and serious complications."
The Wisconsin Sleep Cohort study is funded by the National Institutes of Health.
"In addition to strengthening the evidence that, over time, sleep-disordered breathing (sleep apnea) can increase the risk of death in adults, these findings suggest that treatment may help lessen the risk of dying from cardiovascular disease," noted Michael J. Twery, PhD, director of the NIH National Center on Sleep Disorders Research.