A US study that followed a random sample of men and women for 18 years showed that those with sleep apnea, where breathing pauses during sleep, had more than three times the risk of death from any cause compared to those who did not, and the risk went up when the condition was not treated.
The study is published in the 1st August issue of the Journal SLEEP and was the work of lead author and investigator Dr Terry Young, professor of epidemiology at the University of Wisconsin-Madison, and colleagues.
Young told the press most previous studies of apnea and mortality have been done on patients referred for clinical evaluation, and this is the first time that a study of the general population has been reported. Young said he and his colleagues 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 [body mass index], age and sex.”
For the 18-year follow-up study, Young and colleagues examined records of 1,522 people taking part in the ongoing Wisconsin Sleep Cohort Study, which started in 1988 and recruited a random sample of community-dwelling men and women aged from 30 to 60 years.
The participants spent one night at the University’s General Clinical Research Center where they underwent a polysomnography, from which their apnea-hypopnea index (AHI) was calculated. The AHI is the average number of breathing pauses (apneas) and reductions (hypopneas) per hour of sleep.
For the follow up, the researchers reviewed state and national death records up to 1st March 2008, and found which participants had died and what was recorded as the cause of death in each case.
The results showed that:
- 63 of the participants (4 per cent) had severe sleep apnea at the start (baseline) of the study: they had an AHI of 30 or more, ranging from 30 to 97 apneas and hypopneas per hour.
- 1,157 people (76 per cent) of the participants had no sleep apnea, and their AHI was under 5.
- 80 deaths were recorded, including 37 attributed to cancer and 25 attributed to cardiovascular disease and stroke.
- 12 (that is about 19 per cent) of the participants with severe sleep apnea died, compared with 46 (about 4 per cent) with no sleep apnea.
- Those participants who had severe sleep apnea had over three times the risk of dying due to any cause compared with people who did not have sleep apnea (hazard ratio 3.2, after controlling for age, sex, and BMI).
- This figure went up to 4.3 when 126 people who reported regular use of continuous positive airway pressure (CPAP) therapy were removed from the calculation.
- Hazard ratios for mortality due to any cause remained high even after adjusting for smoking, alcohol, sleep duration and total cholesterol, and severe sleep apnea was linked to increased mortality regardless of whether participants felt sleepy during the day or not.
- About 42 per cent of the deaths among those with severe sleep apnea (5 of 12 deaths) were attributed to cardiovascular disease or stroke.
- This compared with 26 per cent of deaths among those with no sleep apnea (12 of 46 deaths).
- When the 126 people who reported regular use of CPAP were taken out of the figures, the hazard ratio for cardiovascular mortality climbed from 2.9 to 5.2 for people with severe sleep apnea.
- Although those 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 were not statistically significant, said the researchers.
The researchers concluded that:
“Our findings of a significant, high mortality risk with untreated SDB [sleep-disordered breathing], 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.”
They said the findings suggest that regular use of CPAP may protect people with sleep apnea against cardiovascular death.
“I was surprised by how much the risks increased when we excluded people who reported treatment with CPAP.”
“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,” he added.
“Sleep-Disordered-Breathing and Mortality: Eighteen-Year Follow-Up of the Wisconsin Sleep Cohort.”
Terry Young; Laurel Finn; Paul Peppard; Mariana Szklo; Diane Austin; F. Javier Nieto; Robin Stubbs; Khin Mae Hla.
Journal SLEEP, Volume 31, Issue 8, August 1, 2008.
Sources: Journal abstract, American Academy of Sleep Medicine.
Written by: Catharine Paddock, PhD