There may be a link between sleep apnea and cancer, and research has identified it predominantly in women.
According to the National Heart, Lung, and Blood Institute, sleep apnea is a widespread sleep condition among people in the United States.
A person with this condition will stop and start breathing repeatedly during sleep. This may cause them to wake up and will affect the quality of their rest.
One subtype of this condition — obstructive sleep apnea (OSA) — involves obstruction of the airways as a person sleeps. This is caused by the abnormal relaxation of throat muscles.
Studies show that the number of people receiving a diagnosis of OSA is on the rise. This is a worrying trend since this condition can increase a person's risk of hypertension (high blood pressure), cognitive decline, stroke, and chronic fatigue, among other health problems. Moreover, some research suggests that elements of OSA may promote mechanisms that can increase a person's risk of cancer.
Now, a team of researchers from 12 academic institutions — including University College Dublin in Ireland, and Gothenburg University in Sweden — have analyzed a large dataset corresponding to 19,556 participants to learn more about the possible ties between sleep apnea and cancer risk. The data come from the European Sleep Apnoea Database (ESADA), which includes participants with OSA.
In the new study, the researchers looked at the link between the severity of sleep apnea, blood oxygen concentration levels, and a person's risk of cancer. They also took the impact of biological sex on this association into account. The research findings now appear in the European Respiratory Journal.
"Recent studies have shown that low blood oxygen levels during the night and disrupted sleep, which are both common in OSA, may play an important role in the biology of different types of cancers," says study author Athanasia Pataka, who is an assistant professor at Aristotle University of Thessaloniki in Greece.
"But this area of research is very new, and the effects of gender on the link between OSA and cancer have not been studied in detail before," she explains.
Link stronger among women
Among the ESADA cohort whose medical data the researchers analyzed, 5,789 of the participants were women, and 13,767 were men.
The team first assessed the severity of the participants' sleep apnea by looking at how often a person experienced airway obstruction during sleep. They also looked at how many times per night their blood oxygen levels fell below 90%.
Then, the researchers looked at how many people in the entire cohort had also received a cancer diagnosis. They saw that 388 individuals (or 2% of participants) — of which 160 were women and 228 men — held a serious cancer diagnosis.
They also noticed that the participants with cancer were typically aged 50 or over and less overweight than other participants. The researchers note that the most common form of cancer among women was breast cancer, and among men, it was prostate cancer.
The team looked into sex differences in more detail. They found that women with severe OSA who had lower blood oxygen levels during sleep were more likely to have a cancer diagnosis than women without sleep apnea.
When it came to men, the researchers found that this trend did not apply. They found that men with severe sleep apnea were no more likely to have developed cancer than men without this condition.
"Our study of more than 19,000 people shows that [the] severity of OSA is linked to a cancer diagnosis," says Pataka. She adds that "[t]his link was especially strong in the women that we analyzed, and less so in the men, and suggests that severe OSA could be an indicator for cancer in women, though more research is needed to confirm these findings."
While this study was observational and did not look into cause and effect relationships or possible underlying mechanisms explaining these patterns, the researchers believe that there may be a biological explanation for their findings.
Although Pataka admits that the current "study did not explicitly explore the causes of different cancers," she explains that "cancer may differ between men and women because of factors such as how hormones affect tumor growth; how the different types of cancer that were more prevalent in men and women are affected by low blood oxygen levels; or how gender-specific exposure to cigarette smoking may play a role."
Despite research, no cause for alarm
The researchers note that the findings should be ground enough for doctors to pay extra attention when diagnosing sleep apnea in women. Because women experience a different range of symptoms to men, their condition sometimes remains undetected.
"The classic symptoms of OSA, such as sleepiness, snoring, and stopping breathing during the night time are reported more frequently in men, but other lesser known symptoms like fatigue, insomnia, depression, and morning headaches are more common in women, therefore clinicians should be more careful when evaluating their female patients for possible OSA," Pataka urges.
The researchers note that their findings require confirmation by further studies, given the limitations embedded in their analysis.
They adjusted for certain modifiable factors that can affect a person's cancer risk, such as age, body mass index [BMI], smoking, and alcohol consumption. However, the investigators were unable to account for other important factors, including physical activity levels, marital status, education, or occupation.
Despite the fact that the study adds to the body of evidence suggesting a link between respiratory conditions and the likelihood of developing cancer, other specialists urge individuals with OSA not to worry.
Prof. Anita Simonds, from Royal Brompton and Harefield NHS Foundation Trust in the United Kingdom, who was not involved with the current study, comments that cancer prevalence in the cohort the researchers looked at was actually very low, so the chances that a person's sleep apnea will boost their cancer risk might, in context, be low as well.
"In this study, the overall cancer prevalence was low at just 2%, therefore [obstructive sleep apnea] patients should not be alarmed by this research."
Prof. Anita Simonds