clinical Science zyxwvutsrq (1984) 66, zyxwvuts 103-107 zyxwvutsr 103 zy Calcium malabsorption in elderly women with vertebral fractures: evidence for resistance to the action of vitamin D metabolites on the bowel R. M. FRANCIS, M. PEACOCK, G. A. TAYLOR, J. H. STORER AND B. E. C. NORDIN MRCMineral Metabolism Unit, The General Infirmary, Leeds, zyxw U.K. (Received 14 March12 June 1983; accepted 6 July 1983) zyxw s-w 1. Radio-calcium absorption, plasma 25- hydroxyvitamin D [25-(OH)D] and 1,25-di- hydroxyvitamin D zyxwvuts [ 1,25-(OH)zD] concentrations were measured in 19 elderly women with, and 21 without, vertebral fractures, before and after treat- ment with 25-hydroxyvitamin D3 [25-(OH)D3], to establish whether malabsorption of calcium in elderly women with vertebral fractures has a cause different from that in elderly women without vertebral fractures. 2. Malabsorption of calcium and low plasma 25-(0H)D and 1,25(OH)ZD concentrations were common in both groups of women but there was no significant difference in these variables between the two groups. 3. After treatment with 40pg of 25(OH)D3 daily for 7 days, there was a significant increase in plasma 25(OH)D and 1,25{0H)zD in both groups of women, but radiocalcium absorption increased significantly only in the group without vertebral fractures. 4. Elderly women with vertebral fractures have malabsorption of calcium which is resistant to the action of vitamin D metabolites at concentrations which correct calcium malabsorption in elderly women without vertebral fractures. Key words: calcium absorption, osteoporosis, vitamin D metabolites. Abbreviations: (OH)D, hydroxyvitamin D; FTH, parathyroid hormone. Correspondence: Dr M. Peacock, MRC Mineral Metabolism Unit, The General Infirmary, Leeds LS1 3EX, U.K. Introduction Calcium absorption is lower in women with verte- bral crush fractures than in age-matched normal subjects [l-31 and may contribute to the develop- ment of osteoporosis in such patients. The cause of the reduced calcium absorption in women with vertebral fractures has never been unequivocally established, though several mechanisms have been suggested. Calcium malabsorption may result from an intrinsic defect in the absorption mecha- nism [4]; alternatively it may be caused by low plasma 1,25-dihydroxyvitamin D [1,25-(OH)2D] concentrations due either to a failure of the renal lor- hydroxylase enzyme to respond to parathyroid hormone (PTH) [5] or to suppression of PTH pro- duction by the calcium released from increased bone resorption [6]. We, however, have not found any difference in plasma 25-hydroxyvitamin D [25- (OH)D] and 1,25(OH)zD concentrations in women with and without vertebral fractures [7], although others have demonstrated lower plasma 1,25- (OH)zD concentrations in vertebral fracture cases The difference in calcium absorption between women with and without vertebral fractures is less marked in the elderly because of the decline in calcium absorption in normal subjects with age [ti]. We have previously shown that malabsorption of calcium in the elderly is largely due to low plasma 25-(0H)D concentrations and can be corrected by increasing these into the normal range by treatment with oral 25-hydroxyvitamin D3 [25(OH)D3] [9]. Impaired renal function, which is common in the elderly, is also a significant but relatively less fre- quent cause of calcium malabsorption [9]. To investigate whether malabsorption of calcium in elderly patients with vertebral fractures differs PI.