Lack of oxygen from disrupted rest may be to blame

By Nathan Seppa

Web edition: May 21, 2012
Print edition: June 30, 2012; Vol.181 #13 (p. 9)

Obstructive sleep apnea, a breathing disorder linked to heart disease and depression, may heighten the risk of cancer as well. A two-decade study shows that people with severe sleep apnea could be four times as likely to die of cancer as people without the condition.

“This is a kind of study that provides the opportunity to look at the long-range consequences of sleep apnea,” says Jonathan Samet, a pulmonary physician at the University of Southern California, who wasn’t part of the study team. “What’s surprising is the strength of the association they found,” he says. “This is a startlingly strong association.”

The findings were unveiled May 20 at a meeting of the American Thoracic Society in San Francisco and will appear in an upcoming issue of the American Journal of Respiratory and Critical Care Medicine.

Sleep apnea results when a flap of skin in the throat obstructs air intake, often due to obesity, halting breathing during sleep for at least 10 seconds at a time. Severe apnea is marked by frequent breathing stoppages that rouse a person from deep, restorative sleep and cause the individual to gasp for air. What’s more, the disruptions rob cells of needed oxygen, a condition called hypoxia. This may underlie the cancer link, says study coauthor Javier Nieto, a physician and epidemiologist at the University of Wisconsin–Madison.

Earlier research showed that the skin cancer melanoma grew faster in mice that were subjected to intermittent hypoxia than it did in mice with normal oxygen flow. That work inspired Nieto and his colleagues at Wisconsin to investigate cancer incidence among participants in a long-term sleep study that began in 1988. The 1,522 participants, who were age 30 to 60 at the start of the study, underwent an overnight sleep examination at the outset. Those tests showed that 59 people had severe sleep apnea from the get-go.

By November 2011, after a median follow-up of 18 years, those with severe apnea were 4.8 times as likely to have died of a cancer-related cause. Severe sleep apnea is defined as having an air interruption “every other minute or more,” Nieto says, “which is pretty striking.”

Readings taken at the outset of the original sleep study allowed the researchers to measure how much of the night each volunteer had spent in an oxygen-deficient state. Even after adjusting for other risk factors, those with the most severe hypoxia were nearly nine times as likely to have died of cancer during the ensuing study years than were those with normal-oxygen blood. The effect of using nighttime breathing devices called CPAP machines to control apnea was unclear, since some apnea patients but not all began using them at various times during the study.

Samet says the findings should lead to more research into an apnea-cancer link, especially in obese people. “Certainly in our terribly overweight and obese nation and world, if sleep disordered breathing increases cancer risk, we would want to know that,” he says.