Smoking modestly increases risk for severe COVID-19, research now shows

Smoking modestly increased the risk for severe disease in hospitalized patients with COVID-19, particularly among younger patients without diabetes, according to a systematic review and meta-analysis.

The findings, published in Nicotine & Tobacco Research, contrast with those of an earlier meta-analysis that found no link between cigarette smoking and the severity of COVID-19 among nearly 1,400 patients in China.

In the latest analysis, Antonios Karanasos, MD, PhD, a cardiologist at the University of Athens and Hippokration General Hospital in Greece, and colleagues reviewed 22 studies that included more than 6,300 hospitalized patients with COVID-19. Most patients were from China, but a “considerable number” of American patients were also included, the researchers said.

They found that overall, smoking modestly increased the risk for severe COVID-19 (OR = 1.34; 95% CI, 1.07-1.67). However, the researchers found a difference in the relationship between smoking and disease severity between Chinese studies (n = 4,423; OR = 1.48; 95% CI 1.17-1.87) and American studies (n = 1,887; OR = 0.65; 95% CI, 0.33-1.29).

“This difference may be explained by the higher age and diabetes ratio of the non-Chinese population, which we showed to be important risk moderators, or could be due to further differences in comorbidities and care,” the researchers said.

Specifically, among studies in which less than 15% of the patients had diabetes, smoking increased the risk for severe disease (OR = 1.66; 95% CI, 1.26-2.18). However, among studies in which 15% or more had diabetes, “there was a trend for a negative association” (OR = 0.7; 95% CI, 0.46-1.08), according to the researchers.

Karanasos and colleagues also reported that smoking was not significantly associated with increased mortality from COVID-19.

After restricting their analysis to studies “explicitly reporting current smoking,” the researchers said the association between smoking and disease severity was no longer statistically significant.

“Our study provides evidence supporting the utilization of smoking cessation programs, especially in younger populations, as part of a strategy to minimize the adverse consequences of COVID-19 pandemic,” Karanasos and colleagues wrote. “Although smoking increased the risk of severe disease in hospitalized COVID-19 patients, it is not clear whether this hazard derives from nicotine itself or from other toxic components of tobacco smoke; therefore, a positive or neutral impact of nicotine alone on disease severity cannot be excluded based on the current study.”