Similar efficacy of low and standard doses of transdermal estradiol in controlling bone turnover in postmenopausal women

Objectives. To investigate the effects of a low transdermal estradiol dose on bone metabolism and to compare it with both the standard dose and absence of treatment. Methods. In this study performed in a third-level academic center, 66 healthy postmenopausal women underwent hormone therapy (HT) with patches containing estradiol at standard (0.050 mg/day, HT50, 33 women) or low dosage (0.025 mg/day, HT25, 33 women) and 70 women were without treatment (NT). The values (mean of three samples) of several bone biochemical parameters were compared between groups after adjusting for confounding factors. Bone mineral density (BMD) was assessed (by dual-energy X-ray absorptiometry) in the spine and hip in all cases, and a second densitometry scan was performed in 44 women. Results. Bone turnover markers tended to show lower values in the treated groups, but significance was restricted to total alkaline phosphatase (NT vs. HT25, p < 0.05) and cross-linked N-telopeptides of type I collagen (NTX) (NT vs. HT25, p < 10(-6); NT vs. HT50, p < 10(-5)). The loss of BMD observed in NT women, as assessed by the annual percentage change, was blocked in both the HT25 and HT50 women. No significant differences were detected between both HT groups. Conclusions. Low and standard dosages of transdermal estradiol were equally effective in controlling bone metabolism, as assessed by turnover markers. Additionally, NTX was confirmed as the most sensitive marker for detecting changes in bone resorption.