Long-term effects of transdermal and oral hormone replacement therapy on postmenopausal bone loss

Transdermal hormone replacement therapy (HRT) is now an accepted form of treatment, but the long-term skeletal effects have not been assessed. Sixty-six early postmenopausal women were randomized to receive either transdermal HRT (continuous 17 beta-oestradiol 0.05 mg/day, with 0.25 mg/day of norethisterone acetate added for 14 days of each 28-day cycle) or oral HRT (continuous conjugated equine oestrogens 0.625 mg/day, with 0.15 mg/day dl-norgestrel added for 12 days of each 28-day cycle). Treatment was given for 3 years and 30 matched untreated women were studied concurrently as a control group. Bone density was measured in the lumbar spine and proximal femur by dual-photon absorptiometry at 6-monthly intervals. Bone turnover was assessed by measurement of biochemical markers. At 3 years bone density had declined by 4% in the lumbar spine and by more than 5% in the femoral neck in the untreated group. By comparison bone density increased in both treatment groups at both sites (p < 0.001 vs. untreated) and biochemical measurements indicated a significant reduction in bone turnover. There were no significant differences between the treatment groups. Twelve per cent of women on transdermal or oral treatments lost a significant amount of bone from the femoral neck by 3 years despite adequate compliance. Women taking therapy primarily for hip fracture prevention may require a follow-up bone density measurement to establish the efficacy of treatment.