Sleep disordered breathing is associated with an increased risk of cancer mortality

Sleep disordered breathing (SDB), which is associated with an increased risk of adverse cardiovascular events and psychopathological outcomes, is also associated with an increased risk of cancer mortality, according to a new study.

"Recent in vitro and animal studies have shown that repeated episodes of hypoxia (an inadequate supply of oxygen) are associated with accelerated cancer progression," said F. Javier Nieto, MD, PhD, chair of the Department of Population Health Sciences at the University of Wisconsin School of Medicine and Public Health. "Our results are the first to suggest that SDB is also associated with an increased risk of cancer mortality in humans."

The results will be presented at the ATS 2012 International Conference in San Francisco.

The researchers examined 22-year mortality data on 1,522 subjects from the Wisconsin Sleep Cohort, a prospective, community-based study of the predictors and natural history of sleep disorders. SDB was assessed by polysomnography at baseline.

After adjustment for age, sex, body mass index, smoking and other factors, both all-cause and cancer mortality were associated with the presence and severity of SDB in a dose-response fashion. Compared to subjects without SDB, the adjusted relative hazards of cancer mortality were 1.1 for study participants with mild SDB, 2.0 for those with moderate SDB, and 4.8 for those with severe SDB.

The team of University of Wisconsin investigators led by Dr. Nieto conducted this research in collaboration with Ramon Farre, PhD, professor of Physiology at the Unit of Biophysics and Bioengineering at University of Barcelona, Spain. In a separate study which will also be presented at the ATS 2012 conference, Dr. Farre's group and colleagues at the Hospital Clinic-IDIBAPS in Barcelona follow up on their earlier mouse experimental model showing that the effect of intermittent hypoxia on cancer growth is considerably stronger in lean mice than in obese mice.

Overview of Sleep-Disordered Breathing Upper airway obstruction occurring during sleep—that is, sleep-disordered breathing (SDB)—was first demonstrated in the 1960s. SDB represents a group of physiopathologic conditions that are characterized by an abnormal respiratory pattern during sleep that can be isolated or can coexist with other respiratory, nervous, cardiovascular, or endocrine diseases. SDB is now known to be widely prevalent in the general population, and it is responsible for or contributes to numerous problems, ranging from fragmented sleep patterns to hypertension to traffic accidents.

SDB includes obstructive sleep apnea (OSA), which consists of breathing cessations of at least 10 seconds occurring in the presence of inspiratory efforts during sleep. Central sleep apnea consists of similar apneas, but these instead take place in the absence of inspiratory efforts.

The obstructive sleep apnea syndrome (OSAS) is a potentially disabling condition characterized by excessive daytime sleepiness, disruptive snoring, repeated episodes of upper airway obstruction during sleep, and nocturnal hypoxemia. It is defined by an apnea-hypopnea index (the total number of episodes of apnea and hypopnea per hour of sleep), or respiratory disturbance index, of 5 or higher in association with excessive daytime somnolence.