A systematic review of studies by researchers at the University of Warwick has found that people who have been diagnosed with obstructive sleep apnoea could be at an increased risk of adverse outcomes from COVID-19.

The review, published in the journal Sleep Medicine Reviews, emphasises the need for further research into the impact of the SARS-CoV-2 virus, which causes COVID-19, on those with the sleep condition.

The systematic review looked at eighteen studies performed up to June 2020, all of which investigated the relationship between sleep apnoea and COVID-19. Of these studies, eight were mainly related to the risk of death from COVID-19 and ten were related to diagnosis, treatment and management of sleep apnoea.

Despite there being only a few studies specifically looking at COVID-19 and sleep apnoea, the researchers found there is evidence to suggest that many patients in intensive care for COVID-19 had the sleep condition, and in diabetic patients it may exacerbate a risk that is independent from other risk factors.

In one study of patients who had diabetes who were hospitalised with COVID-19, patients who were being treated for obstructive sleep apnoea were at 2.8 times a greater risk of dying on the seventh day after hospital admission.

According to the researchers, in the UK up to 85% of obstructive sleep apnoea disorders are undetected, suggesting that the 1.5 million people currently diagnosed with the condition is just the tip of the iceberg.

“Without a clear picture of how many people have obstructive sleep apnoea it is difficult to determine exactly how many people with the condition may have experienced worse outcomes due to COVID-19,” said Dr Michelle Miller, lead author of the study.

“This condition is greatly underdiagnosed, and we don’t know whether undiagnosed sleep apnoea confers an even greater risk or not.

“It is likely that COVID-19 increases oxidative stress and inflammation and has effects on the bradykinin pathways, all of which are also affected in obstructive sleep apnoea patients. When you have individuals in which these mechanisms are already affected, it wouldn’t be surprising that COVID-19 affects them more strongly,” she added.