Long term effects of oestrogen therapy on bone loss in postmenopausal women: a 23 year prospective study

Objective To determine the long term effect of oestrogen therapy on bone loss after menopause. Design Prospective observational study over 23 years. Setting Malmo, Sweden. Subjects Twenty-eight women taking oestrogen and 196 women not taking oestrogen during the follow up. Methods Bone mineral density of the forearm was measured by single-photon absorptiometry at age 48 and 72 years. Use of oestrogen therapy was noted. Main outcome measure Rate of forearm bone loss between the age of 48 and 72 years. Results Women taking oestrogen, for a median of 17 years (range 4 to 26), had 8.7 percentage points (95% CI 3.8-13.5) lower rate of bone loss compared with women not taking oestrogen during the same period. Each year of oestrogen therapy reduced the rate of bone loss by 0.8 percentage points (95% CI 0.2-1.4). Conclusions The use of oestrogen seems to reduce the rate of bone loss over a period of 23 years, and the longer the duration of the therapy, the less bone loss.