Obstructive sleep apnea, in which people stop breathing for short periods while sleeping. Breathing pauses last from seconds to minutes and may occur 30 times per hour, after which normal breathing then starts again, often with a snoring or choking sound.

About five percent of adults have some form of sleep apnea. It can ncrease the risk of high blood pressure, heart attack and arrhythmias. It is most prevalent in obese people and some studies have also postulated that obstructive sleep apnea may be linked to cancer because of low levels of oxygen in the blood. 

To understand whether obstructive sleep apnea is associated with cancer development, researchers undertook a study of 10,149 patients with the disorder who underwent a sleep study between 1994 and 2010. They linked this information to health administrative databases from 1991 to 2013. At the start of the study, 520 (5.1%) had a cancer diagnosis.

In the study follow-up period (median 7.8 years), 627 (6.5%) people who did not have cancer at baseline had incident cancer. Prostate, breast, colorectal and lung cancers were the most common. 

After controlling for cancer risk factors, the researchers found no apparent causal link between obstructive sleep apnea and cancer.

"There is a need for a sufficiently large cohort study with a long enough follow-up to allow for the potential development of cancer that adjusts for important potential confounders, examines common cancer subtypes and has a rigorous assessment of both obstructive sleep apnea and cancer," writes Dr. Tetyana Kendzerska, Institute for Clinical Evaluative Sciences (ICES) and Women's College Hospital, University of Toronto, Toronto, Ont., with coauthors. 

"We were not able to confirm previous hypotheses that obstructive sleep apnea is a cause of overall cancer development through intermittent hypoxemia [low blood oxygen levels]," write the authors. "However, in subgroup analyses, we found that the level of oxygen desaturation was associated with the development of smoking-related cancer."

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The HeartBEAT Study. Susan Redline