TUESDAY, Sept. 28, 2021 (HealthDay News) — Smoking seems to have a causal effect on the risk for severe COVID-19, according to a study published online Sept. 27 in Thorax.

Ashley K. Clift, M.B.B.S., from the University of Oxford in the United Kingdom, and colleagues conducted a large-scale observational analysis and Mendelian randomization analyses using U.K. Biobank data. The associations between smoking status and confirmed severe acute respiratory syndrome coronavirus 2 infection, COVID-19-related hospitalization, and COVID-19-related death were examined. Data were included for 421,469 participants and for 1,649 confirmed infections, 968 COVID-19-related hospitalizations, and 444 COVID-19-related deaths.

The researchers found that current smokers had elevated risks for hospitalization compared with never-smokers (odds ratio, 1.80) and for mortality (odds ratios, 2.14, 5.91, and 6.11 for smoking one to nine, 10 to 19, and 20+ cigarettes/day). In Mendelian randomization analyses of 281,105 White British participants, the risks for infection and hospitalization were increased for a genetically predicted propensity to initiate smoking (odds ratios, 1.45 and 1.60, respectively). There was also an association for a genetically predicted higher number of cigarettes smoked per day with increased risks for all outcomes (odds ratios, 2.51, 5.08, and 10.02 for infection, hospitalization, and death, respectively).

“The congruence of observational analyses indicating associations with recent smoking behaviors and Mendelian randomization analyses indicating associations with lifelong predisposition to smoking and smoking heaviness support a causal effect of smoking on COVID-19 severity,” the authors write.

Several authors disclosed financial ties to the pharmaceutical and medical technology industries.

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