In the first study, researchers found:
- The presence of mild sleep apnea was associated with a 10% increase in death from cancer
- Moderate sleep apnea was associated with a doubling of the risk of cancer death
- Severe sleep apnea was associated with a nearly five-fold increase in death from cancer
These two studies mark the first time that sleep apnea and cancer have been linked in humans. But previous studies have found this link in animals. Researchers at the University of Barcelona investigated the link between OSA and cancer in mice. They found what when mice with melanoma were deprived of oxygen periodically, their melanoma tumors grew more quickly than mice that were not deprived of oxygen.
This kind of periodic oxygen deprivation -- known as hypoxia -- is the fundamental characteristic of obstructive sleep apnea. When a person has OSA, his or her airway collapses during sleep, depriving the body of oxygen for a short period of time. Breathing is interrupted, and the levels of oxygen in the blood drop. The severity of sleep apnea is determined by how frequently these periods of interrupted breathing occur. Mild sleep apnea is generally regarded as 5-15 breathing interruptions per hour of sleep, while moderate sleep apnea is measured at 15-30 interruptions per hour of sleep. Severe sleep apnea is considered anything over 30 periods of interrupted breathing per hour of sleep.
It is important to note that neither study established sleep apnea as a direct cause of developing cancer or dying from cancer. What each of these studies did is establish an association between the presence and severity of sleep apnea, and the risk of both developing and dying from cancer. These studies represent an important breakthrough in our understanding of the effects of sleep apnea and oxygen deprivation during sleep. They are a significant first step, and additional research will -- and should -- undoubtedly follow.