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Researchers found no link between cigarette smoking and the severity of COVID-19 among cases in China, according to results of a preliminary meta-analysis published in the European Journal of Internal Medicine.A previous report of 44,672 cases in China revealed a higher mortality rate in men compared with women (2.8% vs. 1.7%), which some hypothesized to be caused by a higher prevalence of comorbidities such as smoking among men, Giuseppe Lippi, MD, of the clinical biochemistry department of neuroscience biomedicine and movement at the University of Verona in Italy, and Brandon Michael Henry, MD, PhD, a research fellow at The Heart Institute in the Cincinnati Children's Hospital Medical Center, wrote. In China, 52.1% of men are reportedly smokers vs. 2.7% of women.

“However, decreased levels of angiotensin converting enzyme 2, the reported host receptor of the virus responsible of COVID-19, are observed in smokers,” the researchers wrote.Lippi and Henry reviewed five studies totaling 1,399 patients. Among them, there were 288 patients whose COVID-19 disease was considered severe.Active smoking was a significant predictor of COVID-19 severity in only one study, according to the researchers. But overall, the link was not significant. “Despite a trend toward higher risk was appreciable, no significant association could neither be found between active smoking and severity of COVID-19 when data of individual studies were pooled (OR, 1.69; 95% CI, 0.41–6.92),” Lippi and Henry wrote.

A sensitivity analysis excluding the largest study yielded similar results. “In conclusion, the results of this preliminary meta-analysis based on Chinese patients suggest that active smoking does not apparently seem to be significantly associated with enhanced risk of progressing towards severe disease in COVID-19,” the researchers wrote.