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Abstract
Nephrolithiasis is a common and important condition. Several lines of evidence suggest that increased urinary calcium increases the risk of kidney stones. Since dietary calcium raises urinary calcium, it has been common practice to reduce calcium intake in stone-formers who hyperabsorb calcium from the intestine, although no trial has yet been designed to directly demonstrate the effectiveness of calcium restriction.
In contrast, some have suggested that calcium restriction may be harmful due to resultant hyperoxaluria and risk of bone loss. In fact, two powerful prospective observational studies have suggested that increased dietary calcium reduces the risk of the first kidney stone. However, calcium was not the only variable, since those with the highest quintile of calcium intake also ingested more fluid, potassium, magnesium and phosphate. Moreover, the otherwise thorough analysis was not adjusted for alkali intake, which may prevent stones, or oxalate intake, which may increase stone risk.
Due to limitations in available data, future prospective studies should be designed to probe the effect of specific interventions with calcium, both dietary and supplemental, on urinary parameters and stone formation, particularly in hypercalciuric stone-formers, who may respond conversely. For now, dietary calcium should be gradually increased in stone-formers as guided by the urinary calcium, and hypocalciuric agents should be added as necessary.
Key teaching points:
• Nephrolithiasis is a common and important condition.
• High urinary calcium is a risk factor for stone disease and low bone density.
• Urinary calcium is increased by sodium, calcium and acid load and decreased by phosphate and alkali load.
• Observational studies suggest that high calcium intake prevents an initial stone event, but these patients also ingested more fluid, potassium, magnesium and phosphate.
• Current recommended calcium intake for the general population is three to four servings of dairy daily.
• Calcium intake in hypercalciuric stone-formers should be one serving of dairy with gradual increments to three servings a day as guided by the urinary calcium. Thiazides are often additionally necessary.
Key teaching points:
• Nephrolithiasis is a common and important condition.
• High urinary calcium is a risk factor for stone disease and low bone density.
• Urinary calcium is increased by sodium, calcium and acid load and decreased by phosphate and alkali load.
• Observational studies suggest that high calcium intake prevents an initial stone event, but these patients also ingested more fluid, potassium, magnesium and phosphate.
• Current recommended calcium intake for the general population is three to four servings of dairy daily.
• Calcium intake in hypercalciuric stone-formers should be one serving of dairy with gradual increments to three servings a day as guided by the urinary calcium. Thiazides are often additionally necessary.
Notes
This work was presented at the 39th Annual Meeting of the American College on Nutrition, Symposium II: The Role of Calcium in Prevention of Chronic Diseases, Albuquerque, New Mexico, October 2, 1998.
