Being a current smoker or having a chronic obstructive pulmonary disease (COPD) are associated with an increased risk of severe complications and higher death risk from COVID-19 infection, according to a study.

COPD is a common, persistent dysfunction of the lung associated with a limitation in airflow.

The researchers from the University College London in the UK noted that an estimated 251 million people worldwide are affected by COPD.

Given the effects of the SARS-CoV-2 coronavirus on respiratory function, they sought to understand the prevalence and the effects of COPD in COVID-19 patients.

COVID-19 patients with COPD had a 63 percent risk of severe disease and a 60 percent risk of mortality.

The study, published in the journal PLOS ONE, systematically searched databases of scientific literature to find existing publications on the epidemiological, clinical characteristics and features of COVID-19, and the prevalence of COPD in COVID-19 patients.

As many as 123 potentially relevant papers were narrowed to 15 that met all quality and inclusion guidelines, the researchers said.

The included studies had a total of 2,473 confirmed COVID-19 patients, they said.

The study found that critically ill COVID-19 patients with COPD had a 63 percent risk of severe disease and a 60 percent risk of mortality.

On the other hand, critically ill patients without COPD had only a 33.4 percent risk of severe disease, and 55 percent risk of mortality, the researchers said.

Current smokers were also 1.45 times more likely to have severe complications compared to former and never smokers, they said.

The study was not able to examine whether there was an association between the frequency of COPD exacerbations, or severity of COPD, with COVID-19 outcomes or complications.

The researchers noted that the results are limited by the fact that few studies were available to review, as well as the diverse locations, settings, and designs of the included studies.

"Despite the low prevalence of COPD and smoking in COVID-19 cases, COPD and current smokers were associated with greater COVID-19 severity and mortality," the researchers added.