Can dietary calcium affect stone formation?
About 70 percent of stones are calcium-based. We used to recommend that everyone who had calcium-based stones decrease their calcium intake. We no longer recommend lowering the calcium intake, however, because calcium is important for the operation of muscles and for bone strength, and because some calcium in the diet is even good for preventing kidney stone formation. Calcium and a chemical called oxalate, which is found in fruits and vegetables, bind very tightly together, and form some of the hardest kidney stones. And oxalate is a much stronger promoter of stone growth and formation than calcium. If you don't eat enough calcium, the oxalate in your intestinal tract will not be bound up by calcium, so more of this oxalate will be available for absorption. As a result, if you decrease your calcium intake, you end up raising your risk of stones by increasing the amount of oxalate that is absorbed.
Are some calcium supplements better for people with a history of kidney stones than others?
There is some evidence that calcium citrate may be a slightly better calcium supplement for calcium stone-formers. The theory is that the citrate portion of that particular supplement—being a stone inhibitor—tends to negate any stone-promoting effect from the calcium. I'm not sure how significant this is, but it seems to make sense, so usually I will recommend calcium citrate to my kidney stone patients who need a calcium supplement.
