Sleep Apnea Tied to Increased Cancer Risk

Two new studies have found that people with sleep apnea have a higher risk of cancer. The new research marks the first time that sleep apnea has been linked to cancer in humans.

The first study, of about 1,500 government workers in Wisconsin, showed that those with the most breathing abnormalities at night had five times the rate of dying from cancer as people without the sleep disorder.

Recent animal studies have suggested that sleep apnea might play a role in cancer. When mice with tumors were placed in low-oxygen environments that simulate the effects of sleep apnea, their cancers progressed more rapidly. Scientist speculate that depriving mice of oxygen may cause their bodies to develop more blood vessels to compensate, an effect that could act as a kind of fertilizer for cancer tissue and cause tumors to grow and spread more quickly.

The researchers wondered whether a similar relationship might exist in people with sleep apnea, in whom throat muscles collapse during sleep, choking off the airway and causing gasping and snoring as the body fights for air. Severe sleep apnea can produce hundreds of such episodes each night, depleting the body of oxygen.

The researchers found that the more severe a person's breathing problems were at night, the greater the likelihood of dying from cancer. People with moderate apnea were found to die of cancer at a rate double that of people without disordered breathing at night, while those in the severe category died at a rate 4.8 times that of those without the sleep disorder.

In the second study, researchers with the Spanish Sleep Network took a slightly different approach, looking not at cancer mortality among apnea patients, but at the incidence of cancer. They used a measure called the hypoxemia index, which looks at the amount of time the level of oxygen in a person's blood drops below 90 percent at night. About 5,200 people were followed for seven years, none of whom had a cancer diagnosis when the study began. The researchers found that the greater the extent of hypoxemia, or oxygen depletion, during sleep, the more likely a person would receive a cancer diagnosis during the study period.

People whose oxygen levels dropped below 90 percent for up to 12 percent of the total time they were asleep, for example, had a 68 percent greater likelihood of developing cancer than people whose oxygen levels did not plummet at night. As time spent without oxygen increased, so, too, did cancer risk.

Although the study did not look for it, researchers speculated that treatments for sleep apnea like continuous positive airway pressure, or CPAP, which keeps the airways open at night, might reduce the association.

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