TORONTO -- COVID-19 patients who have been diagnosed with obstructive sleep apnea may have a greater risk of adverse outcomes from the virus, according to a new U.K. study.

Researchers at the University of Warwick conducted a systematic review of studies that looked at COVID-19 patients and found that those who also had sleep apnea were at a higher risk of developing serious complications and dying.

"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 apnea patients," lead author Dr. Michelle Miller said in a press release.

"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.

According to the study, obstructive sleep apnea is a condition characterized by complete or partial blockage of the nasal airways during sleep when the muscles become relaxed. It is commonly diagnosed in people who snore or appear to stop breathing while sleeping.

While there are limited studies on the link between the nasal condition and the novel coronavirus, researchers say many of the risk factors associated with sleep apnea, such as diabetes, obesity and hypertension, are similar to those associated with poorer COVID-19 outcomes.

The findings were published Monday in the journal Sleep Medicine Reviews.

The review looked at 18 studies up to June that reported outcomes for COVID-19 patients with obstructive sleep apnea. Of these studies, eight focused on the risk of death from COVID-19 and 10 were related to diagnosis, treatment and management of sleep apnea.

Researchers found in one large study of patients that had diabetes and were also hospitalized for COVID-19, those being treated for obstructive sleep apnea were at a 2.8 times greater risk of dying after being in intensive care for seven days.

Researchers behind the study say it is important that those diagnosed with sleep apnea are aware of the potential additional risks they may face if they contract COVID-19.

However, the review suggests that treatment for obstructive sleep apnea with continuous positive airway pressure (CPAP) did have some beneficial effects on these individuals.

At least 1.5 million people in the U.K. are currently diagnosed with obstructive sleep apnea, but researchers say up to 85 per cent of sleep apnea disorders are undetected.

"Without a clear picture of how many people have obstructive sleep apnea it is difficult to determine exactly how many people with the condition may have experienced worse outcomes due to COVID-19," Miller said in the release.

Miller said people with sleep apnea should take additional measures to protect themselves against COVID-19, such as wearing a face mask, adhering to physical distancing and getting tested if they have symptoms. She added that these individuals should also be following their sleep apnea treatment plan "as diligently as possible."

The study acknowledged that more research is still needed to determine whether individuals with obstructive sleep apnea should be added to the list of vulnerable groups.

"Hospitals and doctors should also be recording whether their patients have obstructive sleep apnea as a potential risk factor, and it should be included in studies and outcomes data for COVID-19. We need more data to determine whether this is something we should be more concerned about," she said.