Objective: To ascertain the influence of estrogen replacement therapy (ERT) on blood and urinary zinc in postmenopausal women.
Methods: Thirty-seven postmenopausal women aged 53.2 +/- 3.7 years were examined. All were treated with conjugated estrogens 0.625 mg and medroxyprogesterone acetate 5 mg. Zinc, magnesium, calcium, phosphate, and alkaline phosphatase levels in blood were measured before and after 6 and 12 months of treatment. Urinary excretion of zinc, magnesium, calcium, phosphate, and hydroxyproline were evaluated before and after 3, 6, and 12 months of therapy. Bone mineral density was examined before treatment and after 1.7 +/- 0.3 years of ERT. Subjects were classified by 1) initial bone mineral density values (osteoporotics less than 0.850 g/cm2) and 2) zinc excretion as elevated (greater than 600 micrograms/g creatinine).
Results: At baseline, the values of most markers of bone turnover were higher in the osteoporotic women (Hotelling test, P = .06). After 1 year of treatment, a higher decrease of most indices was observed in the osteoporotic patients, and no statistical difference was found between the osteoporotic and the normal groups (Hotelling test, P = .31). A consistent negative association was observed between changes in bone mineral density and urinary zinc excretion in the osteoporosis group. Estrogen replacement therapy reduced excretion of zinc, magnesium, and hydroxyproline in the elevated zinc excretion group. Zinc excretion decreased 35% after 3 months and 26% after 1 year of treatment. The serum tests, with the exception of alkaline phosphatase, showed only negligible changes during ERT.
Conclusion: A significant decrease in zinc excretion was observed after 3 months of ERT. This change was more pronounced in women with osteoporosis and elevated zinc excretion. Because zinc excretion is almost uninfluenced by variation in diet, it may be used as an additional marker of changes in bone metabolism.