Madison, WI - An 18-year follow-up study has found that untreated sleep-disordered breathing (SDB) increases the risk for mortality threefold, according to the results of a study reported in the August 1, 2008 issue of Sleep [1].

"SDB is a treatable but markedly underdiagnosed condition of frequent breathing pauses during sleep," write Dr Terry Young (University of Wisconsin-Madison) and colleagues. "SDB is linked to incident cardiovascular disease, stroke, and other morbidity. However, the risk of mortality with untreated SDB, determined by polysomnography screening, in the general population has not been established."

The cohort for this 18-year mortality follow-up study came from the population-based Wisconsin Sleep Cohort (n=1522). Participants underwent baseline polysomnography to detect SDB, which was characterized by the number of apnea and hypopnea episodes per hour of sleep. Cutoff points at 5, 15, and 30 episodes per hour of sleep identified mild, moderate, and severe SDB, respectively. All-cause and cardiovascular mortality risks associated with SDB severity level, after adjustment for potential confounding factors, were estimated with the Cox proportional hazards regression.

After adjustment for age, sex, body-mass index (BMI), and other clinical variables, the risk for all-cause mortality significantly increased with SDB severity. For severe SDB, compared with no SDB, the adjusted hazard ratio (HR) for all-cause mortality was 3.0 (95% CI 1.4-6.3). When the 126 people who had been treated with continuous positive airway pressure (CPAP) were excluded, the adjusted HR for all-cause mortality for severe SDB, compared with no SDB, was 3.8 (95% CI 1.6-9.0) and the adjusted HR for cardiovascular mortality was 5.2 (95% CI 1.4-19.2). Accounting for daytime sleepiness did not change these results.

"Our findings of a significant, high mortality risk with untreated SDB, independent of age, sex, and BMI, underscore the need for heightened clinical recognition and treatment of SDB, indicated by frequent episodes of apnea and hypopnea, irrespective of symptoms of sleepiness," the study authors write.

Limitations of this study include a lack of information about consistent CPAP use over time and the effectiveness of air pressure level to prevent airway closure, the lack of randomization, a cohort that was 95% white and fully employed, and the inability to determine how CPAP contributes to lower death rates and how long participants had SDB before baseline.

"Although further studies are needed to quantify the proportion of mortality that could be lowered by prevention or treatment of SDB, the results of our study can be applied directly to current healthcare practice," the study authors conclude.