MENOPAUSAL CHANGES IN CALCIUM BALANCE PERFORMANCE

Abstract

Ca balance as a function of both intake and absorption of Ca from the diet was measured 274 times in 168 normal perimenopausal women. Comparisons were made between groups of women segregated according to menopausal and estrogen therapy status. As previously reported, there is a statistically significant positive correlation between Ca balance and both Ca intake and Ca absorption. In 207 studies in premenopausal women Ca balance averaged -0.0199 gm/day; in 41 studies in postmenopausal women untreated with estrogen, Ca balance averaged -0.043 gm/day (P < 0.02). The balance difference was due almost equally to decreased absorption from the diet and to increased urinary excretion. Estrogen-treated postmenopausal women (26) exhibited balance performance indistinguishable from that of the premenopausal group. In 16 women studied twice (5 yr apart) and who went through menopause between studies, Ca balance shifted by -0.0307 gm/day (P < 0.05) as compared with 72 women also studied twice (but without change in menstrual status), in whom mean balance did not significantly change. Ca intake requirement for 0 balance was calculated for both the estrogen-replete and estrogen-deprived groups. Premenopausal and treated postmenopausal women exhibited an intake requirement of 0.990 gm/day Ca; the untreated postmenopausal women had an apparent requirement of 1.504 gm/day (P < 0.01). There is a specific estrogen-related shift in Ca performance across menopause. The reason for the positive effect of estrogen on balance and intake requirement is a combination of enhancement of intestinal absorption efficiency and improved renal Ca conservation.