Obstructive sleep apnoea (OSA) has now been linked to the development of cancer in men younger than age 65, although the researchers acknowledge the relatively small number of people in the study may have distorted the statistics. The worrying findings of the study seem to be limited to men younger than 65 years, although the incidence of OSA related cancer in women and those over 65 could simply be because of the relatively small size of the study.
They researchers do say, and we agree, that the associations which were discovered are worthy of further study. Especially when you look at the likely cause and effect...
The study, published in the American Journal of Respiratory and Critical Care Medicine, analysed 4,910 individuals who were assessed for suspected OSA. These people were then followed for 4.5 years.
"We found an increased cancer incidence (i.e., occurrence of a new cancer) in OSA patients exhibiting nocturnal hypoxia, as compared with those who did not experience nocturnal hypoxia,” said Dr Campos-Rodríguez, the lead researcher.
This is bad news for untreated OSA sufferers. Hypoxia is the technical term for unhealthily / dangerously low blood oxygen levels. It is one of the most specific indicators for OSA, because people with untreated OSA frequently stop breathing hundreds of times per night, for as much as a couple of minutes at a time while asleep. Blood oxygen levels plummet as a result.
As a rough guideline, healthy people in normal conditions have oxygen saturation levels of between 96% and 99%. We have seen OSA sufferers with blood oxygen levels as low as 58%. At that level, their mental function is seriously impaired and, frankly, it’s a miracle they are conscious.
The point being, hypoxia reportedly plays an important role in tumour formation and progression, says Dr Francisco Campos-Rodríguez, of the Sleep-Disordered Breathing Unit at Hospital de Valme, Sevilla, Spain.
He also noted that a recent study showed that when mice were subjected to an intermittent hypoxia pattern mimicking OSA, the growth rate of melanoma tumours was twice that in control animals who were not subjected to hypoxia. The mice subjected to intermittent hypoxia also showed more pulmonary metastases (spread of disease) than the control group.
These findings prompted the researchers to perform a multicenter study in a large sleep cohort to investigate whether OSA is associated with increased cancer incidence in humans.
It appears that the longer a person lives with low night time oxygen levels, the greater the risk of developing a cancer. "For example," Dr Campos-Rodríguez said, "compared with patients who spent <12% of the night time with low oxygen levels, those who spent >12% of the time with low oxygen levels (oxygen saturation of less than 90%) had more than twice the risk of having a cancer during the follow-up period."
More work, they say, is needed to investigate whether a specific cancer location or subtype is more likely to be associated with OSA and the potential role of continuous positive airway treatment (CPAP) in this relationship.
"CPAP is the treatment of choice for OSA patients. This treatment avoids upper airway collapse and its consequences, including intermittent hypoxia. Unfortunately, we did not assess the effect of CPAP treatment in our cohort," Dr Campos-Rodríguez said. "Therefore, although one may speculate that if CPAP avoids intermittent hypoxia associated with OSA, it would possibly have a protective effect against this outcome, whether CPAP reduces cancer incidence in OSA patients needs to be investigated."