WESTCHESTER, Ill. – Moderate to severe obstructive sleep apnea (OSA) is an independent risk factor for all-cause mortality, according to a study in the August 1 issue of the journal Sleep.
Fourteen years after initial data were collected, about 33 percent of participants with moderate to severe sleep apnea had died (six of 18 individuals), compared with 6.5 percent of people with mild OSA (five of 77) and 7.7 percent of people with no OSA (22 of 285). The association between moderate to severe OSA and mortality remained significant after statistical adjustment for other risk factors, producing a fully adjusted hazard ratio of 6.24 for all-cause mortality; mild OSA was not a risk factor for mortality.
"This is the first study to demonstrate an independent association between all-cause mortality and sleep apnea in a community-based study," said lead author Nathaniel Marshall, PhD, a postdoctoral fellow at the Woolcock Institute of Medical Research in Sydney, Australia. "The size of the increased mortality risk was surprisingly large. In our particular study a six-fold increase means that having significant sleep apnea at age 40 gives you about the same mortality risk as somebody aged 57 who doesn't have sleep apnea."
According to Marshall, previous studies that have linked OSA to mortality as an independent risk factor have involved patients referred to sleep clinics rather than community-based samples; the association between OSA and mortality in the community was unknown.
The study involved 380 men and women between the ages of 40 and 65 who were already involved in the Busselton Health Study, an ongoing survey of residents in the rural town of Busselton in the state of Western Australia. From November to December 1990, each participant used a portable home-monitoring device for one night to assess his or her level of sleep-disordered breathing.
Individuals were categorized according to the frequency of recorded respiratory disturbance. Only three participants had severe OSA with an average of 30 or more respiratory disturbances per estimated hour of sleep, while 18 individuals (about 4.7 percent) had moderate to severe OSA with 15 or more respiratory disturbances per hour. Seventy-seven participants (about 20.3 percent) had mild OSA with five to 14 respiratory disturbances per hour, and 285 people (75 percent) had no OSA.
State and national death records were reviewed through 2004 to identify participants who had died and to note the cause of death listed on the death certificates. From the records of the 33 study participants who died, no predominant cause of death could be linked to OSA.
Initial results were adjusted for other mortality risk factors such as age, sex, body mass index, smoking status, blood pressure, cholesterol and diabetes. All statistical models produced a significant relationship between sleep apnea and mortality. No information was gathered about participants' use of any sleep apnea treatment.
According to Marshall, the results of this study indicate that OSA is a potentially life-threatening condition that demands increased medical attention.
"Our findings, along with those from the Wisconsin Cohort, remove any reasonable doubt that sleep apnea is a fatal disease," he said. "People who have, or suspect that they have, sleep apnea should consult their physicians about diagnosis and treatment options."
The study was supported by grants from the Australian National Health and Medical Research Council.
According to the American Academy of Sleep Medicine, most people with OSA snore loudly and frequently, with periods of silence when airflow is reduced or blocked. They then make choking, snorting or gasping sounds when their airway reopens. About 80 percent to 90 percent of adults with OSA remain undiagnosed.
The most common treatment for OSA is continuous positive airway pressure (CPAP) therapy, which provides a steady stream of air through a mask that is worn during sleep. This airflow keeps the airway open to prevent pauses in breathing and restore normal oxygen levels.
A media fact sheet about obstructive sleep apnea is available from the AASM at http://www.aasmnet.org/Resources/FactSheets/SleepApnea.pdf. Information from the AASM for patients and the public is available about OSA at http://www.sleepeducation.com/Disorder.aspx?id=7 and about CPAP at http://www.sleepeducation.com/CPAPCentral/.
Sleep is the official journal of the Associated Professional Sleep Societies, LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.
For a copy of the study, "Sleep Apnea as an Independent Risk Factor for All-Cause Mortality: The Busselton Health Study," or to arrange an interview with an AASM spokesperson, please contact Kathleen McCann, AASM director of communications, at (708) 492-0930, ext. 9316, or kmccann@aasmnet.org.
Journal Sleep Fact Sheet: Obstructive Sleep Apnea & Mortality
Comparing the Wisconsin Sleep Cohort with the Busselton Health Study
Journal Sleep – August 1, 2008
Two studies in the August 1 issue of the journal Sleep link obstructive sleep apnea (OSA) to mortality risk. This fact sheet compares the design and results of the two studies.
Study Design
Wisconsin: Random, population-based sample of adults who were recruited from several Wisconsin state agencies.
Busselton: Community-based sample of residents in the rural town of Busselton in the state of Western Australia.
Note: Previous studies linking OSA to mortality involved sleep-clinic patients instead of population samples.
Study Group
Wisconsin: 1,522 adults between the ages of 30 and 60 years
Busselton: 380 adults between the ages of 40 and 65 years
Sleep Assessment
Wisconsin: One night of in-lab, 18-channel polysomnography conducted at the University of Wisconsin General Clinical Research Center
Busselton: One night of at-home, 4-channel portable monitoring
Primary Measurement
Wisconsin: Sleep apnea or "sleep-disordered breathing," measured by the apnea-hypopnea index (AHI) – per hour of sleep, the average number of apneas (breathing pauses of 10 seconds or more) and hypopneas (breathing reductions with a decrease in blood oxygen saturation of four percent or more).
Severe (AHI 30 or more), Moderate (AHI 15 to 29), Mild (AHI 5 to 14), No sleep apnea (AHI less than 5)
Busselton: Obstructive sleep apnea, measured by the respiratory disturbance index (RDI) – per estimated hour of sleep, the average number of oxygen desaturations of three percent or more that were accompanied by an increased heart rate of 10 or more beats per minute and/or a burst of snoring at the beginning and end of the desaturation event.
Moderate-Severe (RDI 15 or more), Mild (RDI 5 to 14), No OSA (RDI less than 5)
Mortality Follow-Up
Wisconsin: Eighteen years, reviewing state and national death records up to March 1, 2008.
Mean follow-up: 13.8 years. Total observation: 20,963 person-years
Busselton: Fourteen years, reviewing state and national death records through 2004.
Mean follow-up: 13.4 years. Total observation: 5,073 person-years
Deaths
Wisconsin: Total: 80 of 1,522 individuals (5.3%). Severe sleep apnea: 12 of 63 (19%).
Moderate: 6 of 82 (7.3%). Mild: 16 of 220 (7.3%). No sleep apnea: 46 of 1,157 (4%).
Busselton: Total: 33 of 380 individuals (8.7%). Moderate-Severe OSA: 6 of 18 (33%).
Mild OSA: 5 of 77 (6.5%). No OSA: 22 of 285 (7.7%).
All-Cause Mortality Hazard Ratios
Wisconsin: Severe sleep apnea: 3.2. Moderate sleep apnea: 1.3. Mild sleep apnea: 1.5.
Adjusted for age, sex and body mass index. Hazard ratios were significantly increased with SDB severity. Adjusted hazard ratios remained high after further adjustments for smoking, alcohol use, general health status, educational status, neck girth, waist:hip ratio, sleep duration and total cholesterol.
Busselton: Moderate-Severe OSA: 6.24. Mild OSA: 0.47.
Adjusted for age, sex, body mass index, smoking, total cholesterol, HDL cholesterol, diabetes, angina and blood pressure. After controlling for all the same risk factors except blood pressure, the hazard ratio for moderate-severe OSA was 4.4. Only moderate-severe OSA was statistically significant.
Effect of Continuous Positive Airway Pressure (CPAP) Therapy
Wisconsin: When 126 participants who reported regular CPAP use were removed from the statistical analysis, the adjusted hazard ratio for all-cause mortality related to severe sleep apnea jumped from 3.2 to 4.3. The adjusted hazard ratio for cardiovascular mortality related to severe sleep apnea soared from 2.9 to 5.2. These results suggest that CPAP was protective particularly against cardiovascular death.
Busselton: The people living in Busselton did not have regular access to sleep medicine services, and treatment with CPAP was probably rare. The untreated all-cause mortality hazard ratio of 4.3 seen in the Wisconsin cohort is very similar to the hazard ratio of 4.4 observed in the most comparable analysis from the Busselton study.
Journal
SLEEP