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Sleep apnoea linked to cancer mortality

21st May 2012

Researchers in the United States say that people who suffer from sleep apnoea, which has already been linked to higher risks of heart disease and high blood pressure, may also be at a higher risk of dying of cancer.


The study, which only applies to existing cancer patients, found that people with the most severe sleep apnoea--defined as having 30 or more episodes of low or no oxygen in an hour of sleep--are almost five times more likely to die of cancer than someone without sleep apnoea.

According to Javier Nieto, chair of the department of population health sciences at the University of Wisconsin School of Medicine and Public Health in Madison, sleep apnoea is the periodic pausing of breathing during sleep that results in drops in oxygen levels in your blood.

It gives rises to snoring and drowsiness during waking hours, and has been identified as a severe health problem, not just an irritation to partners, family members or neighbours.

Drowsiness and daytime sleepiness mean that a person is at an increased risk of accidents. But sleep apnoea has also been linked to cardiovascular disease, heart disease, strokes, hypertension and cardiovascular mortality.

Nieto will soon present his team's findings at an international conference of the American Thoracic Society in San Francisco.

Nieto's research was carried out in collaboration with scientists at the University of Barcelona in Spain, who reported in an earlier study that skin cancer tumours grew faster in mice that were deprived of oxygen from time to time.

He also cited earlier laboratory studies which showed that cancer cells that were deprived of oxygen produce molecules that stimulate the growth of blood vessels in an attempt to get more oxygen.

Working with the Barcelona researchers, Nieto reviewed data from more than 1,500 enrolled in the Wisconsin Sleep Cohort, which included 22 years of mortality data, as well as information from sleep studies.

They wanted to test whether or not a similar result would be found in people.

They found that, once the data was adjusted to take age, sex, body mass, smoking and other factors into account, sleep apnoea still increased the risk of cancer death in direct proportion to the severity of the sleep apnoea.

People with severe sleep apnoea were 4.8 times more likely to die of cancer than those with no sleep apnoea. The risk was 10% higher in patients with the mildest sleep apnoea, and double in patients with moderate sleep apnoea, defined as more than 15 and less than 30 of low or zero oxygen per hour.

The study does not prove a cause-and-effect link, although the findings have been consistent in cellular, animal and human studies.

According to Steven Park, sleep medicine specialist and otorhinolaryngologist at Montefiore Medical Centre in New York City, the findings were consistent with existing research on the link between sleep apnoea and chronic disease.

He called for further research to confirm the findings, however, and stressed that the study had not yet been published in a peer-reviewed medical journal.

Park said anyone who snored or complained of severe daytime fatigue or memory and concentration problems should be screened for sleep apnoea. In women, the condition was more likely to exist in the absence of snoring.


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