Family History of Kidney Stones? Watch Those Megadoses of Vitamin C

New York, NY
September 22, 1997

Kidney stones are a common problem, affecting about half a million people each year. Men are more prone to kidney stones than women -- nearly four out of five sufferers are men. Dietary habits may sometimes increase the risk of developing kidney stones. If you or anyone in your family has had a kidney stone, consider the following:

Taking high doses of vitamin C supplements, such as 500 mg or more a day on a regular basis, has been shown to increase the risk of developing kidney stones in some people. This is particularly true in people who have had calcium oxalate stones in the past or who have a family history of these stones. The reason for this may be that, at high doses, a significant amount of vitamin C is converted to oxalate in the body. A large amount of oxalate would then be present in the urine where it could combine with calcium to form calcium oxalate stones. "People who are at risk for this problem should not take more than the recommended daily allowance of vitamin C (60 mg) as a supplement," says Garabed Eknoyan, MD, president of the National Kidney Foundation.

Eating foods that are high in oxalate may also trigger kidney stone formation in people who are prone to develop calcium oxalate stones. The following foods have been shown to increase oxalate in the urine, and they should be avoided by these individuals: spinach, rhubarb, beets, nuts (including peanut butter), chocolate, tea, wheat bran and strawberries.

If you are concerned about whether you may be at risk for developing calcium oxalate stones, speak to your doctor. You may also get additional information about kidney stones by calling the National Kidney Foundation at (800) 622-9010.