People with severe sleep apnea have a much higher mortality risk than people without sleep apnea, and this risk increases when sleep apnea is untreated.
Results show that people who have severe sleep apnea, which involves frequent breathing pauses during sleep, have three times the risk of dying due to any cause compared with people who do not have sleep apnea.
This risk is represented by an adjusted hazard ratio of 3.2 after controlling for age, sex and body mass index. When 126 participants who reported regular use of continuous positive airway pressure (CPAP) therapy were removed from the statistical analysis, the hazard ratio for all-cause mortality related to severe sleep apnea rose to 4.3.
“We found that both men and women with sleep apnea in the general population – not patients – mostly undiagnosed and untreated, had poorer survival compared with persons without sleep apnea, given equal BMI, age and sex,” said principal investigator and lead author Terry Young, PhD, professor of epidemiology at the University of Wisconsin-Madison.
According to Young, most previous studies of sleep apnea and mortality have involved patients referred for a clinical sleep diagnostic evaluation; the mortality risk for sleep apnea in the general population has not been previously reported.
The study was an 18-year follow-up of 1,522 participants in the ongoing Wisconsin Sleep Cohort Study, which was established in 1988 and involved a random sample of men and women from the community who were between the ages of 30 and 60 when the study began. After spending one night at the University of Wisconsin General Clinical Research Center for assessment by polysomnography, participants were categorized by apnea-hypopnea index (AHI), which is the average number of breathing pauses (apneas) and reductions (hypopneas) per hour of sleep. Sixty-three individuals (about four percent) had severe sleep apnea at baseline with an AHI of 30 or more and a range of 30 to 97 apneas and hypopneas per hour. About 76 percent of the study group (1,157 individuals) had no sleep apnea with an AHI of less than five.
For the follow-up study, state and national death records were reviewed up to March 1, 2008, to identify participants who had died and to note the causes of death listed on the death certificates. Eighty deaths were recorded, including 37 deaths attributed to cancer and 25 deaths attributed to cardiovascular disease and stroke.
About 19 percent of participants with severe sleep apnea died (12 deaths), compared with about four percent of participants with no sleep apnea (46 deaths). Although participants with mild sleep apnea (AHI of five to 14) or moderate sleep apnea (AHI of 15 to 29) had a mortality risk that was 50 percent greater than those with no sleep apnea, the results did not achieve statistical significance.
Hazard ratios for all-cause mortality remained high after further adjustments for other factors such as smoking, alcohol use, sleep duration and total cholesterol. Severe sleep apnea was associated with increased mortality whether or not participants experienced daytime sleepiness.
About 42 percent of deaths in people with severe sleep apnea (5 of 12 deaths) were attributed to cardiovascular disease or stroke, compared with 26 percent of deaths in people with no sleep apnea (12 of 46 deaths). When the 126 participants who reported regular CPAP use were removed from the analysis, the hazard ratio for cardiovascular mortality soared from 2.9 to 5.2 for people with severe sleep apnea. The results suggest that regular CPAP use may protect sleep apnea patients against cardiovascular death.
“I was surprised by how much the risks increased when we excluded people who reported treatment with CPAP,” Young said. “Our findings suggest – but cannot prove – that people diagnosed with sleep apnea should be treated, and if CPAP is the prescribed treatment, regular use may prevent premature death.”
Statistical adjustments show that high blood pressure, cardiovascular disease, stroke and diabetes may play a role in the association between sleep apnea and mortality, but the specific mechanisms by which sleep apnea contributes to mortality remain unclear.
The study was supported by grants from the National Institutes of Health.
Source: American Academy of Sleep Medicine, USA