Smoking Prevalence and COVID-19 in Europe

Abstract

Introduction: This ecological study investigates the association between smoking prevalence and COVID-19 occurrence and mortality in 38 European nations as of May 30, 2020.

Methods: Data were collected from Our World in Data. Regression analysis was conducted to adjust for potential confounding factors such as economic activity (gross domestic product), the rate of COVID-19 testing, and the stringency of COVID-19 control policies.

Results: There was a statistically significant negative association between smoking prevalence and the prevalence of COVID-19 across the 38 European nations after controlling for confounding factors (p = 0.001). A strong association was found between the prevalence of COVID-19 per million people and economic activity (p = 0.002) and the rate of COVID-19 testing (p = 0.0006). Nations with stricter policy enactment showed fewer COVID-19 cases per million people, but the association was not significant (p = 0.122). Delaying policy enactment was associated with a greater prevalence of COVID-19 (p = 0.0535). Evidence of a direct association between smoking prevalence and COVID-19 mortality was not found (p = 0.626). There was a strong positive association between COVID-19 mortality rate and the prevalence of COVID-19 cases (p < 0.0001) as well as the proportion of the population over 65 years of age (p = 0.0034) and a negative association with the rate of COVID-19 testing (p = 0.0023).

Conclusions: We found a negative association between smoking prevalence and COVID-19 occurrence at the population level in 38 European countries. This association may not imply a true or causal relationship, and smoking is not advocated as a prevention or treatment of COVID-19.

Implications: Given the evidence of this ecological study, and of several other studies that found an underrepresentation of smoking prevalence in hospitalized cases, it may be worth examining, in laboratory experiments and controlled human trials, if nicotine offers any protection against COVID-19. Most importantly, to date, no study, including this one, supports the view that smoking acts as a treatment intervention or prophylaxis to reduce the impact or ameliorate the negative health impacts of COVID-19.

Figure 1.

Number of smokers versus COVID-19 cases in European nations. All variables were transformed to natural logarithms. COVID-19 cases per million people was adjusted for the influence of other confounding factors and standardized against standardized number of smokers per million people. The partial correlation coefficient is −0.576 (p < 0.001) with a 95% confidence interval (−0.761, −0.306), very similar to the simple Pearson correlation coefficient −0.575 (p < 0.001) with a 95% CI (−0.756, −0.313), indicating that the confounding factors controlled for did not distort the simple linear association that had been detected, either because these confounding factors are uncorrelated with the smoking prevalence rate or have an offseting impact on the COVID-19 prevalence when the smoking rate was correlated with the confounding factors. Smoking prevalence was negatively correlated with the rate of COVID-19 testing but was positively correlated with Max Stringency-Index.