Calcium malabsorption in the elderly: the effect of treatment with oral 25-hydroxyvitamin D3.

Calcium malabsorption is common in the elderly and may contribute to the development of age-related bone loss. To investigate its cause, we have measured radio-calcium absorption, plasma 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and parathyroid hormone in forty-eight elderly women with a normal plasma creatinine. Calcium malabsorption was associated with low 25-hydroxyvitamin D concentrations and was corrected by increasing these into the normal range by treatment with oral 25-hydroxyvitamin D3. Treatment also increased 1,25-dihydroxyvitamin D, and decreased parathyroid hormone concentrations. Before treatment, plasma parathyroid hormone was related to plasma creatinine but not to 25-hydroxyvitamin D, and the change in absorption on treatment correlated inversely with plasma creatinine. 51Cr EDTA clearance was measured in sixteen elderly women and confirmed that renal impairment was common even with a plasma creatinine in the normal range. Our results suggest that calcium malabsorption in the elderly is predominantly due to vitamin D deficiency; renal impairment is also common and contributes to the malabsorption by increasing the requirements for vitamin D.