People with obstructive sleep apnea (OSA) have an elevated risk of cancer, according to a large study presented at the European Respiratory Society (ERS) International Congress in Barcelona, Spain.
A second study showed that OSA was also linked to a decline in processing powers in the elderly; in particular, those aged 74 years or more and men showed a steeper decline in certain cognitive tests.
A third study found that patients with more severe OSA were at greater risk of developing blood clots in their veins – a potentially life-threatening condition. OSA is a common sleep disorder whereby people experience partial or complete obstruction of their airways during sleep and stop breathing several times a night. This can manifest as loud snoring, gasping, choking and daytime sleepiness.
It is believed to affect at least 7-13% of the population. People who are overweight or obese, have diabetes, or who smoke or consume large amounts of alcohol are most at risk of OSA.
Dr Andreas Palm, a researcher and senior consultant at Uppsala University, Sweden, who presented the first study, said: “It is known already that patients with obstructive sleep apnoea have an increased risk of cancer but it has not been clear whether or not this is due to the OSA itself or to related risk factors for cancer, such as obesity, cardiometabolic disease and lifestyle factors. Our findings show that oxygen deprivation due to OSA is independently associated with cancer.”
Dr Palm and colleagues looked at data from 62,811 patients five years prior to the start of treatment for OSA in Sweden. Between July 2010 and March 2018, patients were treated with continuous positive airway pressure (CPAP), which provides a positive pressure of air through a mask to keep the airways open during sleep. The researchers linked these data with data from the Swedish National Cancer Registry and socio-economic data from Statistics Sweden.
The researchers took account of factors that could affect the results such as body size, other health problems and socio-economic status. They matched 2,093 patients with OSA and a diagnosis of cancer up to five years before OSA diagnosis with a control group of 2,093 patients with OSA but no cancer. They measured the severity of OSA with the apnoea hypopnea index (AHI), which measures the number of breathing disturbances during sleep, or the oxygen desaturation index (ODI), which measures how many times an hour levels of oxygen in the blood fall by at least 3% for ten seconds or longer.
“We found that patients with cancer had slightly more severe OSA, as measured by an apnoea hypopnea index average of 32 versus 30, and an oxygen desaturation index of 28 versus 26,” he said. “In further analysis of subgroups, ODI was higher in patients with lung cancer (38 versus 27) prostate cancer (28 versus 24) and malignant melanoma (32 versus 25).
“The findings in this study highlight the need to consider untreated sleep apnoea as a risk factor for cancer and for doctors to be aware of the possibility of cancer when treating patients with OSA. However, extending screening for cancer to all OSA patients is not justified or recommended by our study results.”
The study only looked at data from one point in time and it cannot show that OSA causes cancer, only that it is associated with it. Some important lifestyle factors such as physical activity and food preferences were not captured on an individual basis in the study. The main strength of the study is its large size and the high quality of data on cancer diagnosis and OSA.
In the future, Dr Palm and his colleagues plan to increase the number of patients and to follow the patients over time to study the potential influences of CPAP treatment on cancer incidence and survival. “The association between OSA and cancer is less well established than the link with diseases of the heart and blood vessels, insulin resistance, diabetes and fatty liver disease,” he said. “Therefore, more research is needed, and we hope our study will encourage other researchers to research this important topic.”