Previous studies have linked the sleep disordered breathing (SBD) problems to hypertension, cardiovascular disease, depression and earlier death, but this is the first to find a link to cancer.
Lead author Dr. F. Javier Nieto, chair of the Department of Population Health Sciences at the University of Wisconsin School of Medicine and Public Health commented that the study had subjects with severe SBD had five times higher incidence of cancer deaths, more than just a statistical anomaly. Previous studies in animals have shown similar results, while other studies have linked cancer to possible lack of oxygen or anaerobic cell activity over long periods of time, therefore, it's possible poor breathing fails to oxygenate the cells sufficiently.
Dr. Nieto, an expert in sleep epidemiology continued:
"Clearly, there is a correlation, and we are a long way from proving that sleep apnea causes cancer or contributes to its growth ... But animal studies have shown that the intermittent hypoxia (an inadequate supply of oxygen) that characterizes sleep apnea promotes angiogenesis-increased vascular growth - and tumor growth. Our results suggest that SDB is also associated with an increased risk of cancer mortality in humans."
Dr. Nieto presented his study at the American Thoracic Society 2012 International Conference in San Francisco on May 20th. His study was supported by the National Institutes of Health's the National Heart, Lung, and Blood Institute (NHLBI), the National Institute on Aging, and the former National Center for Research Resources. Dr. Susan B. Shurin, acting director of the National Heart, Lung and Blood Institute commented on her interest in the findings:
"These findings provide clues to help further our understanding of the relationship between sleep and health ... It will be important to understand the relationship and mechanisms, if the association is confirmed."
Dr. Nieto and his team at the University of Wisconsin-Madison made their research in collaboration with Dr. Ramon Farré, professor of physiology at University of Barcelona, Spain, who presented a separate but highly relevant study at the ATS conference. Dr. Farre's team demonstrated that intermittent hypoxia on cancer growth is considerably stronger in lean mice than in obese mice.
The Wisconsin scientists looked at the 22 year mortality rate of over 1,500 subjects, taking data from the Wisconsin Sleep Cohort, a longitudinal, community-based epidemiology study of sleep apnea and other sleep problems that began in 1989 under the leadership of Dr. Terry Young. The doctor is also a member of the UW health sciences faculty.
Those in the study, which started out with local state workers, undergo overnight monitoring that include polysomnography, an all-night recording of sleep and breathing - and many other tests at four-year intervals. The studies are conducted in a specially designed unit at the federally funded UW Institute for Clinical and Transitional Research Center (ICTR).
Nieto's team then adjusted the results to take into account, age, sex, smoking habits and body mass index.126 of the subjects had to be excluded because they used continuous positive airway pressure, but still the results came in nearly 5 times higher than amongst those with no sleep breathing problems.
Dr. Nieto concludes that:
"In our large population-based sample, SDB was associated with an elevated risk of cancer mortality ... Additional studies are needed to replicate these results. If the relationship between SDB and cancer mortality is validated in further studies, the diagnosis and treatment of SDB in patients with cancer might be indicated to prolong survival."