Effect of estrogen on intestinal strontium absorption in postmenopausal women

Objectives: there is considerable uncertainty about the underlying cause of decreased intestinal calcium absorption that occurs in postmenopausal women. In a previous study, estrogen treatment did not result in an increased intestinal calcium absorption using strontium as a marker. A possible explanation could be that the calcium/strontium load given to the women was too high (600 mg Ca), which might result in an insensitive test with respect to the possible stimulation of active strontium transport by estrogen. Therefore, the purpose of this study was to reinvestigate the effect of estrogen on active intestinal strontium absorption using a load of 2.5 mmol of strontium only. Methods: the effect of estrogen on intestinal strontium absorption was measured in eight normal postmenopausal women. The study included two baseline strontium absorption tests, which were performed with an interval of 10 days for calculating the within subject variation (SER). Thereafter the effect of 2 months of estrogen treatment on intestinal strontium absorption was assessed. Fractional absorption (FC₂₄₀) and the area under the concentration time curve (AUC) 4 h after an oral strontium load of 2.5 mmol were calculated. Results: the within subject SER of FC₂₄₀ and AUC^0-240 were 2.3±0.76 and 1.2±0.41, respectively. FC₂₄₀ and AUC^0-240 of strontium were unchanged after treatment with estrogen. Conclusions: in normal postmenopausal women, we did not find a modulating effect of short-term treatment with a (supra) physiological dose of estrogen on intestinal calcium absorption as measured by the strontium absorption test.