APSS: Sleep Apnea Increases Risk of Death

By Michael Smith
BALTIMORE, 13 june 2008--reathing in sleep causes significant mortality, according to researchers here.In a long-running population-based study in Wisconsin, those with severe sleep-disordered breathing at baseline had a 3.2-fold increase in risk of death from any cause compared with people whose sleep breathing was normal, found Terry Young, Ph.D., of the University of Wisconsin in Madison.During 18 years of follow-up in the study, those with severe sleep-disordered breathing had a mortality rate of 14.6 per 1,000 person-years, compared with 2.85 for those whose sleep breathing was normal, Dr. Young said at SLEEP 2008, the meeting of the Associated Professional Sleep Societies.
"Untreated sleep apnea," Dr. Young concluded, is "significantly associated with increased risk of death."
The Wisconsin Sleep Cohort recruited 1,522 participants, ages 30 through 60, and tested them with overnight polysomnography at baseline and every four years thereafter, Dr. Young said.
They were divided into four groups, based on the apnea-hypopnea index, which divides the number of awakenings per night by the number of hours of sleep.
For this analysis, those with an apnea-hypopnea index below five were considered to be normal, while those from five through 14 were classified as having mildly disordered breathing.
Those from 15 through 19 were said to have moderate sleep-disordered breathing and those 30 or above were classified as severe. Sleep apnea is usually defined as an apnea-hypopnea index of greater than 15.
Using Social Security and Wisconsin death records, the investigators found that after 20,963 person-years of follow-up, 80 of the original cohort had died.
Cox regression analysis, adjusted for body mass index, age and sex, showed that compared to participants with an apnea-hypopnea index below five, the hazard ratio for death from any cause was 3.2 (with a 95% confidence interval from 1.6 to 6.8). The trend over the four groups was significant at P=0.005.
When the 126 participants using continuous positive airway pressure were excluded -- those treated for sleep apnea, in other words -- the hazard ratio for all-cause mortality jumped to 4.3 for the most severely affected and the trend was significant at P<0.001. p="0.03."

In this untreated subgroup, the risk for cardiovascular death was also increased. Compared to those without disordered breathing, those with the most severe apnea had a hazard ratio for cardiovascular death of 5.2. The 95% confidence interval was 1.4 to 19.1 and the trend was significant at P=0.03.
One implication of that analysis is that continuous positive airway pressure may reduce the risk of death in people with severe sleep apnea, Dr. Young said.
Another study reported here supported the notion that sleep apnea increases cardiovascular risk.
Researchers on the MrOS study, whose main goal is to look at osteoporotic fractures in men, conducted in-home polysomnography on 2,905 men with an average age of 76.4 years, according to Katie Stone, Ph.D., of California Pacific Medical Center in San Francisco.
On the basis of the results, they were stratified into those with an apnea-hypopnea index of below 15 and those with an apnea-hypopnea index of 15 or higher. There were 718 cardiovascular events in 2.5 years of follow-up.
Dr. Stone reported that men whose apnea-hypopnea index was 15 or higher had a 2.8-fold increased risk of heart failure compared to those in the lower group (with a 95% confidence interval from 1.4 to 5.4).
Taken together, the two studies confirm the dangers of sleep apnea, according to James Krainson, M.D., of Pulmonary Physicians of South Florida in Miami, who was not involved with either study.
"We always knew it was bad for your health, but the link with mortality hadn't been proved as definitively as now," Dr. Krainson said. "The more data we have, the more we know it's real."
The "clinical lesson" is that more physicians -- especially those in primary care -- need to be aware of the risks of sleep apnea for their patients and to do more to treat them, he said.

Primary source: Associated Professional Sleep Societies meetingSource reference:Stone KL, et al "Sleep disordered breathing and incident cardiovascular events in older men: the MrOS sleep study" APSS Meeting 2008; Abstract 885.