Canadian researchers have found no apparent connection between sleep apnea and cancer in a new study of more than 10,000 people with this common sleep disorder.
People with sleep apnea experience repeated periods of disrupted breathing during sleep. Studies suggesting a link between the condition and cancer risk theorized that low oxygen levels might trigger cell mutations connected with cancer.
"We were not able to confirm previous hypotheses that obstructive sleep apnea is a cause of overall cancer development through intermittent lack of oxygen," said lead author Dr. Tetyana Kendzerska, from the Institute for Clinical Evaluative Sciences and Women's College Hospital at the University of Toronto.
The report, published Aug. 5 in the Canadian Medical Association Journal, is unlikely to put the question to rest, however.
"Additional studies are needed to find out whether there is an independent effect of sleep apnea on specific types of cancer," Kendzerska said.
Dr. Leonard Lichtenfeld, deputy chief medical officer of the American Cancer Society, said the findings suggest that sleep apnea by itself is not related to an increased risk of cancer. "However, for some people the factors that cause sleep apnea are related to an increased risk of cancer," he said.
Risk factors for sleep apnea include smoking, chronic lung disease, obesity and diabetes, Lichtenfeld said. "It is these conditions that are more likely to cause the increased cancer risk seen in other studies, not the sleep apnea itself," he said.
This study isn't the "final answer," he said. "More research will have to be done."
For the study, Kendzerska and colleagues studied about 10,150 patients suffering from sleep apnea who took part in a sleep study between 1994 and 2010. They linked this data to health databases from 1991 to 2013.
At the start of the study, about 5 percent of the patients had cancer. Over an average of nearly eight years of follow-up, an additional 6.5 percent of the participants developed cancer. Most common were prostate, breast, colorectal and lung cancers, the researchers said.
Although no link was seen for cancer in general, the researchers did find that low oxygen levels related to sleep apnea were associated with smoking-related cancers, such as lung cancer.
Dr. Yosef Krespi, director of the Center for Sleep Disorders at Lenox Hill Hospital in New York City, cautioned that while sleep apnea may not cause cancer, it is a serious condition that needs to be treated.
"One should not ignore sleep apnea," Krespi said. "Sleep apnea is a chronic progressive disorder that if left untreated can result in serious heart problems."
More than 18 million American adults have sleep apnea, according to the National Sleep Foundation. Some experts say the condition is increasing because of the obesity epidemic.
Sleep apnea can make a cancer patient's life more difficult, Krespi said.
"The quality of life of sleep apnea patients with cancer and their ability to tolerate treatments such as chemotherapy and radiation can be very different than those without the condition," he said.