Influence of age and obesity on serum estradiol, estrone, and sex hormone binding globulin concentrations following oral estrogen administration in postmenopausal women.

Objective: Hormone therapy (HT) increases the risk of venous thrombosis and stroke. Risk of venous thrombosis and stroke is higher in older, overweight, and obese women using HT. However, the impact of age and obesity on estrogen concentrations among HT users is not well defined.

Method: We measured serum levels of estrone, total and free estradiol, and SHBG in 180 postmenopausal women participating in the Estrogen in the Prevention of Atherosclerosis Trial (EPAT), 91 receiving estradiol therapy (ET) and 89 taking placebo, every 6 months over 2 yr. Mean on-trial levels of estrogens and SHBG were compared across age, body mass index (BMI), and waist to hip ratio categories among ET users and placebo separately.

Results: Among the ET users, total (P = 0.01) and free estradiol (P = 0.002) were significantly directly associated with BMI adjusted for age. SHBG was inversely related to waist to hip ratio adjusted for age (P = 0.005). Age was not associated with any of the estrogen or SHBG concentrations in ET or placebo groups. BMI was positively associated with estrone concentrations among older but not younger ET users (P for interaction = 0.03).

Conclusion: Overweight and obese women using ET attain greater concentrations of estrogen compared to women with normal BMI, whereas ET users with abdominal obesity attain lower SHBG levels. Obese older women using ET have the highest concentration of estrone. It may be useful to consider age and obesity when prescribing HT to minimize the risk of venous thrombosis or stroke in postmenopausal women. Further research regarding relationships among circulating hormone levels and risk for these conditions is required to substantiate this conclusion.