Sleep Apnea Linked to Higher Cancer Death Risk
Cancer compensates, spreads in search for oxygen, researcher suggests
SUNDAY, May 20, 2012 (HealthDay News) -- Sleep apnea has already been linked to a host of adverse health problems, such as high blood pressure and heart disease. Now, new research suggests that in people who already have cancer, the sleep disorder may raise their risk of dying from cancer.
People with the most severe sleep apnea -- those who have 30 or more episodes of low or no oxygen in an hour of sleep -- had almost five times the risk of cancer death compared to someone without sleep apnea.
"Sleep apnea is the periodic pausing of breathing during sleep that results in drops in oxygen levels in your blood. It causes snoring and sleepiness during the day," explained study author Dr. Javier Nieto, chair of the department of population health sciences at the University of Wisconsin School of Medicine and Public Health, in Madison.
"Aside from being an annoyance to your spouse, family members and maybe even your neighbors depending on how loud your snoring is, sleep apnea is a severe problem. Drowsiness and sleepiness during the day increase the risk of accidents, and sleep apnea is associated with cardiovascular disease, heart disease, strokes, hypertension and cardiovascular mortality. Now, we see this new angle: an increase in cancer mortality," said Nieto.
Nieto is scheduled to present the study Sunday at the American Thoracic Society International Conference, in San Francisco.
Nieto said the new study was suggested by researchers from the University of Barcelona in Spain who found that when mice were deprived of oxygen periodically, skin cancer tumors grew faster in the mice. And, cancer cells in the lab that are deprived of oxygen produce molecules that stimulate the growth of blood vessels in an attempt to get more oxygen, he said.
Nieto and the Spanish researchers wondered if this effect was the same in humans. To test that theory, they reviewed data from more than 1,500 people included in the Wisconsin Sleep Cohort. This study included 22 years of mortality data, as well as information from sleep studies.
The researchers adjusted the data to account for age, sex, body mass, smoking and other factors that might affect the risk of cancer death, and they found that sleep apnea increased the risk of cancer death. They also found that the more severe the sleep apnea, the more likely someone was to die from cancer.
People with mild sleep apnea -- five to 14.9 episodes of low or no oxygen in an hour -- had a 10 percent increased risk of cancer death, while those with moderate sleep apnea -- 15 to 29.9 episodes of low or no oxygen in an hour -- had double the risk of cancer death. Those with severe sleep apnea -- more than 30 episodes of low or no oxygen in an hour -- had a 4.8 times higher risk of cancer death.
Nieto said the study didn't prove a cause-and-effect relationship, but the association was quite strong. And, he noted that the findings were consistent in humans, animals and in cells.
He added that there is also a plausible mechanism for this association. When you have cancer and you repeatedly have episodes of low or no oxygen, the cancer cells "try to compensate for the lack of oxygen by growing additional blood vessels to get more oxygen. It's a defense mechanism," Nieto said. And, as those blood vessels keep growing, it helps the tumor to spread, he explained.
Dr. Steven Park, a sleep medicine specialist and otorhinolaryngologist at Montefiore Medical Center in New York City, said he wasn't surprised by the findings.
"This goes along with the link between sleep apnea and pretty much every chronic medical condition out there," Park said. But, he added that this study's findings need to be confirmed in other studies, and ideally be published in a peer-reviewed journal. Research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed medical journal.
"Anyone with snoring, severe daytime fatigue, lack of memory or focus, high blood pressure, diabetes, and even someone who has to get up to go to the bathroom at night should be screened for sleep apnea," Park said. He added that it's possible to have sleep apnea without snoring, especially for women. So, if you're getting enough sleep at night, yet still feel tired during the day, it's important to bring this up to your doctor.
Park said there are home-monitoring devices that can be used to screen people at home initially.
Nieto said that treating sleep apnea will improve your quality of life, as well as reduce your risk of high blood pressure and cardiovascular disease. And, if you have cancer, he said, treating sleep apnea may help increase your odds of surviving cancer.
Learn more about sleep apnea from the U.S. National Heart, Lung and Blood Institute.