Intestinal hyperabsorption of calcium and low bone turnover in hypercalciuric postmenopausal osteoporosis

Hypercalciuria of intestinal origin has been linked with bone loss in calcium nephrolithiasis and idiopathic osteoporosis. This retrospective data analysis was performed to explore potential pathogenetic link between intestinal hyperabsorption of calcium and postmenopausal osteoporosis. Data were retrieved from postmenopausal women who were evaluated for osteoporosis or osteopenia at the Mineral Metabolism Clinic of UT Southwestern Medical Center. A total of 319 patients underwent the test of calciuric response to oral calcium load to obtain an indirect measure of intestinal calcium absorption. Serum and urinary biochemistry and L2-L4 bone mineral density (BMD) were compared between five quintiles of calciuric response. There was a statistically significant trend toward a rise in 24-h urinary calcium and a decrease in urinary deoxypyridinoline (DPD) and BMD, with increasing order of quintiles. The presentation of those in the 1st quintile was consistent with vitamin D insufficiency or deficiency, with impaired calcium absorption, secondary hyperparathyroidism, and stimulated bone turnover (high normal urinary DPD). In contrast, patients in the 5th quintile displayed a picture of absorptive hypercalciuria of stone disease, with intestinal hyperabsorption of calcium, high or high normal urinary calcium and suppressed bone turnover (low or low normal urinary DPD). Thus, the assessment of intestinal calcium absorption in a seemingly homogeneous group of postmenopausal women with osteoporosis or osteopenia revealed a spectrum of calciuric response whose extremes may represent two physiologically distinct subtypes that have important diagnostic and therapeutic implications.