Effect of micronized progesterone on bone turnover in postmenopausal women on estrogen replacement therapy

PURPOSE: To determine whether daily oral micronized progesterone affects bone turnover, as estimated by serum and urine biochemical markers, in postmenopausal women on long-term estrogen replacement therapy (ERT). METHODS: We recruited 14 women aged 65 or older to participate in a 9-week trial with micronized progesterone. Each woman had undergone a hysterectomy and was on unopposed ERT at time of study entry. Women received micronized progesterone 100 mg twice daily in the first week and then received 200 mg twice daily in weeks 2-9. We measured markers of bone turnover in serum and urine collected at baseline and at 3 weeks, 6 weeks, and 9 weeks on treatment. Markers of bone formation were serum bone alkaline phosphatase (BAP), N-terminal procollagen peptides (PINP), and osteocalcin (OC). Markers of bone resorption were urinary cross-linked N-terminal and C-terminal telopeptides of type I collagen. In addition, we measured serum progesterone, estradiol and sex hormone binding globulin, triglycerides, total cholesterol, and high-density lipoprotein (HDL)-cholesterol levels at baseline and at 9 weeks on treatment. RESULTS: Mean serum progesterone levels increased from 1.6 +/- 1.1 to 15.2 +/- 3.9 ng/mL, which was within the luteal phase range (3-25 ng/mL). Crosslinked C-telopeptides of type I collagen and osteocalcin increased significantly (p < 0.05) with progesterone treatment, however, other bone markers did not change. Estradiol, estrone, and SHBG levels did not change with treatment. High-density lipoprotein-cholesterol levels decreased 19% (p < 0.001) at 9 weeks on treatment compared to baseline but total and low-density lipoprotein (LDL) cholesterol and triglycerides did not change with treatment. CONCLUSION: In postmenopausal women on long-term estrogen replacement therapy, micronized progesterone (400 mg/d) increased one marker each of bone resorption and bone formation. Other sensitive markers of bone turnover did not change with treatment. Further, micronized progesterone decreased HDL-cholesterol in these women. Our data do not support a beneficial effect of micronized progesterone on bone or cardiovascular risk factors in postmenopausal women.