Smoking, postmenopausal hormone therapy and the risk of venous thrombosis: a population‐based, case–control study

Abstract

In postmenopausal women, oral hormone therapy (HT) is responsible for more than two venous thrombosis (VT) events per 1,000 person-years of treatment (Rossouw et al, 2002). Recent evidence supports a synergistic effect of smoking and oral contraceptives on the risk of VT (Pomp et al, 2008). Because HT has similar components as oral contraceptives – oestrogen progestogen, albeit in lower doses - smokers could represent a group in whom the VT risk associated with HT is considerably increased. Although no interaction between smoking and HT was found in the Women’s Health Initiative (WHI) clinical trial (Cushman et al, 2004), the small number of smoking VT cases and the selection of healthy participants in that trial may limit the validity and generalizability of this null finding. Our aim was to investigate the presence of this interaction in a large population-based study.