Vitamin D repletion does not alter urinary calcium excretion in healthy postmenopausal women

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Abstract
OBJECTIVE To evaluate, in a posthoc analysis of a previous study, whether vitamin D repletion in postmenopausal women with insufficient vitamin D increases urinary calcium excretion, as vitamin D therapy might contribute to hypercalciuria and calcium stones in susceptible individuals, and the effect of vitamin D on the risk of urolithiasis warrants attention. SUBJECTS AND METHODS We recruited 18 women at ≥5 years after menopause who had vitamin D insufficiency (serum 25(OH)‐vitamin D, 16–24 mg/dL). We excluded women with a history of urolithiasis and kidney disease. Women had one calcium absorption study when vitamin D‐insufficient, received vitamin D therapy, and completed a second calcium absorption study when vitamin D‐replete. We fed subjects meals that mirrored the nutrient composition from self‐reported 7‐day diet diaries. To measure calcium absorption, we collected urine for 24 h during both visits. RESULTS We achieved vitamin D repletion in all women (25(OH)‐vitamin D before and after treatment, 22 and 63 mg/dL, respectively; P < 0.001). The mean calcium intake was 832 mg/day. Residual urine specimens were available for 16 women, allowing a measurement of 24‐h urinary calcium. Calcium excretion did not change after vitamin D therapy (212 before vs 195 mg/day after; P = 0.60). Of four women with hypercalciuria (>247 mg/day), calcium excretion decreased in three (377–312 mg/day, not significant). CONCLUSION Vitamin D supplementation did not increase the urinary calcium excretion in healthy postmenopausal women. Many stone formers are at risk of premature bone loss, vitamin D insufficiency, or both. Based on the present results we suggest a study of patients with hypercalciuria and nephrolithiasis to determine the risks of vitamin D therapy.

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