Take Calcium...More Kidney Stones?

Can calcium supplements promote kidney stones? It's unlikely, according to some new research that looked at the relationship between recommended amounts of calcium and the likelihood of getting kidney stones. In fact, it appears that just the opposite is true. It seems that calcium binds with oxalate to form calcium oxalate in the intestine and prevents much of it from being absorbed into the body.

This is good news because restricting calcium intake has been a mainstay of therapy in preventing stone formation. Seventy-five percent of kidney stones are formed from oxalates found abundantly in some plant foods. Beets, rhubarb, peanuts and chocolate and cocoa are especially high in oxalates. Other good sources are dark green leafy vegetables like spinach, collards and Swiss chard, legumes, tea, and berries.

Lowering calcium intake in an effort to prevent kidney stones increases a person's risk for osteoporosis. In fact, taking in more calcium will bind with most of the dietary oxalates preventing them from getting in the body in the first place. But most of the oxalates to be excreted are made inside the body and are not part of the food intake.

Some individuals are known to be stone-formers in that they make kidney stones more readily than others. In a new study, one of the questions was to see if there were differences between the forms of calcium supplements used. Both calcium carbonate and calcium citrate malate were equally effective in binding with the oxalates. Also the most effective amount was 200 and 300 milligrams (mg) of calcium as compared to only 100 mg. Calcium carbonate is present in most of the tablets available. Calcium citrate malate is the form added to orange juice and is the form most easily absorbed. Also calcium with a meal is more readily absorbed than when it is taken between meals.

This research suggests that getting ample amounts of calcium helps prevent kidney stones and that it is better to take the calcium supplement with meals rather than between meals in order to inhibit oxalate absorption. However, it is best to check with your physician about what is best for you because there may be other reasons why between-meal calcium is recommended in your case.

Sources: Liebman, Michael, and Weiwen Chai. Effect of dietary calcium on urinary oxalate excretion after oxalate loads. Amer J Clin Nutr. 65:1453-9. May 1997. Shils, Maurice E. And Vernon R. Young. Modern Nutrition in Health and Disease, 7th ed. Lea & Febiger, Philadelphia. Pp. 1597-98. 1988.

Mary P. Clarke, Ph.D.
Extension Specialist, Nutrition Education

5/97 FILE: FOOD COMPONENTS/Minerals

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