ANN ARBOR, MICHIGAN. It is commonly believed that a high calcium intake increases the risk of forming kidney stones. Researchers at the Universities of Michigan and Arkansas now provide convincing proof that this contention is wrong and that a high dietary intake of calcium actually reduces the risk of stone formation. Their study involved 1309 women aged between 20 and 92 years. The women's intake of calcium, oxalate-containing foods, and ascorbic acid was estimated using the National Cancer Institute Food Frequency Questionnaire. The women resided in three different communities where the calcium content of the water supply varied between 15 mg/mL and 375 mg/mL. The drinking water also contained fluoride either added (1 ppm) or naturally occurring (4 ppm). Analysis of the collected data showed that women with medically diagnosed kidney stones (44 out of 1309 or 3.4 per cent) had an average intake of 843 mg/day of calcium from food, supplements, and water while women without a history of kidney stones had an average intake of 1070 mg/day. The main difference in calcium intake was associated with food intake rather than with water or supplement intake. There was no significant difference in total fluid intake or intake of oxalate-rich foods between women who had kidney stones and those who had not. Neither was there any association between the intake of ascorbic acid (vitamin-C) and the risk of kidney stones. Bone mineral density and incidence of fractures were no different between women with or without kidney stones when the data was adjusted for age, body mass index, and calcium, oxalate and ascorbic acid intake. The researchers speculate that a high calcium diet may be protective because the calcium binds to the oxalate in the intestines and thereby prevents it from reaching the kidneys. They conclude that increasing the intake of dietary calcium may be protective against kidney stones and that an increased dietary calcium intake is not associated with a greater risk of forming renal stones.
Sowers, MaryFran R., et al. Prevalence of renal stones in a population-based study with dietary calcium, oxalate, and medication exposures. American Journal of Epidemiology, Vol. 147, May 15, 1998, pp. 914-20