Smoking and venous thromboembolism: a Danish follow-up study

Background: Large-scale prospective studies are needed to assess whether smoking is associated with venous thromboembolism (VTE) (i.e. deep venous thrombosis and pulmonary embolism) independently of established risk factors. Objective: To investigate the association between smoking and the risk of VTE among middle-aged men and women. Methods: From 1993 to 1997, 27 178 men and 29 875 women, aged 50-64 years and born in Denmark, were recruited into the Danish prospective study 'Diet, Cancer and Health'. During follow-up, VTE cases were identified in the Danish National Patient Registry. Medical records were reviewed and only verified VTE cases were included in the study. Baseline data on smoking and potential confounders were included in gender stratified Cox proportional hazard models to asses the association between smoking and the risk of VTE. The analyses were adjusted for alcohol intake, body mass index, physical activity, and in women also for use of hormone replacement therapy. Results: During follow-up, 641 incident cases of VTE were verified. We found a positive association between current smoking and VTE, with a hazard ratio of 1.52 (95% CI, 1.15-2.00) for smoking women and 1.32 (95% CI, 1.00-1.74) for smoking men, and a positive dose-response relationship. Former smokers had the same hazard as never smokers. Conclusions: Smoking was an independent risk factor for VTE among middle-aged men and women. Former smokers have the same risk of VTE as never smokers, indicating acute effects of smoking, and underscoring the potential benefits of smoking cessation.