BONE DENSITY OF NORMAL WOMEN IN RELATION TO ENDOGENOUS AND EXOGENOUS OESTROGENS

To evaluate the relationship between duration of hormone replacementtherapy (HRT) and forearm bone density, a population-based studyhas been conducted of 4638 women comparing bone density of 1079women who had taken HRT for varying times with those who hadnever taken it. Forearm bone mineral content (BMC) was measuredby single photon absorptiometry. Additionally, free oestradioland sex hormone binding globulin levels were measured in womenwith high and low bone mineral content. There were no detectable differences in BMC in those who tookHRT for up to 24 months compared with those who did not. Thereafterthere were significant positive regression coefficients forduration periods of 2 to 5 yr (ß = 0.77, P = 0.04and ß = 1.76, P = 0.03) and more than 5 yr (ß= 1.66, P<0.0005 and ß = 1.87, P = 0.009) in post-menopausaland oophorectomized women. The major determinants of BMC wereheight, and in post-menopausal or oophorectomized women, age.Weight and parity also had additional explanatory power forpre- and post-menopausal women. Those who were in the highestquintile of BMC but had never taken HRT showed significantlyelevated percentage free oestradiol compared with those in thelowest quintile. Thus HRT is osteoprotective if taken after the menopause formore than 24 months. KEY WORDS: Bone density, Oestrogens, Hormone replacement therapy, Breast cancer, Free oestradiol