No Genetic Causality between Tobacco Smoking and Venous Thromboembolism: A Two-Sample Mendelian Randomization Study.

Background:  Given the current debate in clinical research about the relationship between tobacco smoking and the risk of venous thromboembolism (VTE), a Mendelian randomization (MR) study was conducted aimed at elucidating the causal associations of current and past tobacco smoking with the risk of VTE, from the perspective of genetics.

Methods:  Two-sample univariate and multivariable MR analyses were designed, using summary-level data from large genome-wide association studies involving European individuals. Causality was primarily assessed using multiplicative fixed-effects or random-effects model and inverse variance weighting, supplemented by MR-Egger regression, MR-PRESSO, Cochran's Q test, and leave-one-out for sensitivity analysis to test the reliability of the results.

Results:  In the univariate MR analysis, no significant causal effects were found between current tobacco smoking and the risk of VTE, deep vein thrombosis (DVT), and pulmonary embolism (PE). Similarly, no significant causal effects were found between past smoking and VTE, DVT, and PE. As for the multivariable MR analysis, results were consistent with univariate MR analysis, with no significant causal effect of either current or past tobacco smoking on the risk of VTE, DVT, and PE.

Conclusion:  Evidence from both univariate and multivariable MR analyses demonstrated no significant causal relationships between current and past tobacco smoking and VTE, DVT, and PE. This contradicts positive correlations reported in some previous observational studies, which may be explained by other confounding factors. This provided genetic evidence for the conclusion reported in other observational studies that smoking did not affect VTE risk.