The effects of postmenopausal hormone therapy on serum estrogen, progesterone, and sex hormone-binding globulin levels in healthy postmenopausal women.

OBJECTIVE Differences in disease outcomes between users and nonusers of hormone therapy (HT) and between users of estrogen therapy (ET) and users of estrogen + progesterone therapy (EPT) may relate to differences in serum hormone concentrations between these populations. In this study, we examined the response of serum hormone levels in healthy postmenopausal women after 1 year of HT. METHODS A representative subsample of 200 healthy adherent participants from the active and placebo groups of the Women's Health Initiative randomized controlled clinical trials of ET (conjugated equine estrogens 0.625 mg daily) or EPT (ET plus medroxyprogesterone acetate 2.5 mg daily) were selected for the determination of selected sex hormone levels at baseline and 1 year after randomization. RESULTS In participants receiving active ET intervention compared with placebo, estrogenic hormone levels increased from baseline to year 1 by 3.6-fold for total estrone, 2.7-fold for total estradiol, and 1.8-fold for bioavailable and free estradiol concentrations. Serum sex hormone-binding globulin concentrations also increased 2.5-fold. In contrast, progesterone levels decreased slightly in women taking exogenous EPT. The response of serum estrogens and sex hormone-binding globulin did not differ substantially with the addition of progesterone. In subgroup analyses, hormone response varied by age, ethnicity, body mass index, smoking status, vasomotor symptoms, and baseline hormone levels. CONCLUSIONS These data provide a reference point for the serum hormone response to HT and demonstrate that the response of serum estrogens is similar for ET and EPT. The implications of the slight decrease in serum progesterone levels with EPT therapy are uncertain. Potential treatment interactions for estrogenic hormones were identified, which suggest a larger response to HT in women with low endogenous levels.