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intake from foods and the risk of kidney stone formation remained, but there was no apparent relationship between supplement use and risk. In a study of 50,000 men 40 to 75 years of age (Curhan et al., 1993), the same relationship was evident: reduced risk with increased intake of calcium from food sources, but no association with use of calcium supplements.

The suggested discrepancy between the risks from food sources of calcium and from calcium supplements may in part be due to the timing of the supplement intake (Curhan et al., 2007). Calcium present in the food will bind oxalate, a known contributor to kidney stone formation, and prevent its absorption. If taken between meals, the calcium would have less opportunity to bind oxalate, and so oxalate absorption would be increased. These observations suggest that taking calcium supplements with meals should reduce the formation of kidney stones, but this has not been tested.

Overall, the data indicate that the calcium content of foods does not cause stone formation, but may be protective against it. On the other hand, calcium supplements are emerging as a concern based on observational data, at least for some groups under certain circumstances. Further, individuals with a history of kidney stones are at increased risk if they obtain their calcium from supplements rather than food sources. There is, however, limited evidence from small, short-term trials suggesting that supplemental calcium in moderate doses may not increase risk for stone recurrence. The most important evidence to date is from the WHI trial (Jackson et al., 2006), which indicated that a mean calcium intake from foods and supplements that totaled about 2,150 mg/day—plus a vitamin D supplement of 400 IU/day, a level low enough to avoid potential confounding effects for adverse events given the mean total vitamin D intake of approximately 750 IU/day—resulted in a 17 percent increased incidence of kidney stones among postmenopausal women, regardless of whether the subjects had experienced previous clinical events related to urinary calculi formation.

Nephrolithiasis in Children

Hypercalciuria, as a secondary outcome to high calcium intake, can occur in children as well as in adults. However, the incidence of kidney stones in children is rare. There is limited evidence concerning high calcium intakes in young children relative to calcium excretion. In a study of children ages 1 to 6 years and designed to test the effects of 1,800 mg/day total calcium (supplementation adjusted on the basis of dietary calcium questionnaire), the calcium intake of 1,800 mg/day calcium did not cause urinary calcium/creatinine ratios to differ significantly from those of placebo controls (Markowitz et al., 2004).

A study by Sargent et al. (1999) provides information relevant to infants and calcium excretion. This study supplemented the formula of full-term



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