Smoking and risk of venous thromboembolism: a systematic review.

The relationship between smoking and venous thromboembolism (VTE) is unclear, as a result we conducted a meta-analysis to assess the association between smoking and VTE. A comprehensive search was conducted to identify studies evaluating the relationship between smoking and VTE. Two reviewers independently selected studies and extracted data. The data were analyzed using Comprehensive Meta-Analysis software, version 2. Twenty-one studies were included. Our findings show current smoking (RR 1.24; 95% CI: 1.14-1.35) and former smoking (RR 1.05; 95% CI: 1.01-1.10) were associated with increased VTE risk. There was a dose-response relationship between cigarettes smoked per day and VTE: 1-14 cigarettes/day: RR 1.20; 95% CI: 1.08-1.34, I2 = 0%; 15-24 cigarettes/day: RR 1.33; 95% CI: 1.15-1.54, I2 = 0%; > 25 cigarettes/day: RR 1.63; 95% CI: 1.37-1.95, I2 = 6%. Our findings show smoking is a risk factor for VTE with a dose-response relationship.