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HEALTH & WELLNESS: Vitamin C not culprit with kidney stones

Charlotte Observer


Q. In your article last week, you mentioned that increased vitamin C consumption can promote kidney stones. I was curious if you've read the article at www.vitamincfoundation.org/news.htm#KIDNEY? It states that megadoses of vitamin C do not cause kidney stones.

A. Thank you for your question and the information. I was not aware of this information. The study you are referring to appeared in the Journal of the American Society of Nephrology in 1999. This study involved 85,557 women, with no previous history of kidney stones and covered a 14-year period. It looked at urinary oxalate, an important determinant of calcium oxalate kidney stone formation. The concern is that high doses of vitamin C can convert to oxalate. The study also looked at the increased consumption of vitamin B6 to decrease oxalate stone formation.

In this study, the addition of vitamin C directly into urine will show an increase in oxylates. This means that vitamin C in the urine could convert to oxylates during the actual analytical process. The study included dosing of 1,000 mg to 10,000 mg.

The result of the study was that the use of vitamin C in large doses does not increase the risk of forming kidney stones. Although women form stones at one-third the rate of men, the number involved in the study (85,557) is certainly adequate to make the claim. It appears that the conversion of ascorbate (vitamin C) to oxalate is possibly more of an in-lab conversion than an in-body conversion.

The conflict about the vitamin C goes back to some previous studies. One short-term study of 39 healthy volunteers demonstrated that 50 percent of participants had an increase in urinary oxylates while receiving 1,000 mg of vitamin C daily. No further increase in oxylates was demonstrated by an increase to 9,000 mg of vitamin C.

Keep in mind that just because you have oxylates in the urine does not mean you will form a stone. This is especially true for individuals who stay well-hydrated.

The Recommended Daily Allowance (RDA) for vitamin B6 is 2 mg per day. The RDA is supposed to be the minimum amount of vitamin needed but has nothing to do with optimal health.

The results confirmed that B6 can decrease stone formation. The study demonstrated that increasing B6 in doses of 10 mg to 500 mg per day decreased oxalate stones or stone recurrence rates.

This article is written for general informational purposes only. This information should not be used for a diagnosis, as a recommendation for treatment, nor should it be considered a replacement for consultation with a health-care professional. If you have questions or concerns about your health, please contact your health-care provider.



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