Obesity and risk of venous thromboembolism among postmenopausal women: Differential impact of hormone therapy by route of estrogen administration. The ESTHER Study

Abstract

Background: Oral estrogen use and elevated body mass index (BMI) increase the risk of venous thromboembolism (VTE). Recent data suggest that transdermal estrogenmight be safe with respect to thrombotic risk. However, the impact of transdermal estrogen on the association between overweight (25 kg m-2 < BMI ≤ 30 kg m-2) or obesity (BMI >30 kg m-2) and VTE risk has not been investigated. Methods: Wecarried amulticenter case-control study of VTE among postmenopausal women aged 45-70 years, between 1999 and 2005, in France. Case population consisted of women with a first documented idiopathic VTE. We recruited 191 hospital cases matched with 416 hospital controls and 62 outpatient casesmatched with 181 community controls. Results: The odds ratio (OR) for VTE was 2.5 [95% confidence interval (CI):1.7- 3.7] for overweight and 3.9 (95%CI: 2.2-6.9) for obesity. Oral, not transdermal, estrogen was associated with an increased risk (OR = 4.5; 95% CI: 2.6-7.7 and OR = 1.1; 95%CI: 0.7-1.7, respectively). Compared with non-users with normal weight, the combination of oral estrogen use and overweight or obesity further enhanced VTE risk (OR = 10.2; 95% CI: 3.5- 30.2 andOR = 20.6;95%CI: 4.8-88.1, respectively).However, transdermal users with increased BMI had similar risk as nonusers with increased BMI (OR = 2.9; 95% CI: 1.5-5.8 and OR = 2.7; 95%CI: 1.7-4.5 respectively for overweight; OR = 5.4; 95% CI: 2.1-14.1 and OR = 4.0; 95% CI: 2.1-7.8 respectively for obesity). Conclusions: In contrast to oral estrogen, transdermal estrogen does not confer an additional risk of idiopathic VTE in women with increased BMI. The safety of transdermal estrogen on thrombotic risk has to be confirmed. © 2006 International Society on Thrombosis and Haemostasis.