Vitamin C is ascorbic acid. Some people take extra doses of vitamin C to prevent colds. Some take even more to treat them. Others may take it for other reasons. But if you've ever had a kidney stone, you may want to think twice about taking extra vitamin C supplements.
This study looked only at men and followed more than 22,000 men for more than 10 years. It found that those who took high doses of vitamin C supplements doubled their risk of getting a kidney stone. The increased risk was seen only in those taking extra doses of vitamin C and not in those taking just a multivitamin.
How much vitamin C is too much? Well, that's not exactly clear. This study was done in Sweden, where most vitamin C supplements contain 1000 mg per tablet. The kidney stone risk was highest in those taking more than 7 vitamin C supplements per week.
Why the increased risk? As we know, kidney stones are often composed of calcium oxalate. When excess vitamin C is excreted by the body, it is usually in the oxalate form, and this may lead to more stones.
No link to stones was found for foods high in vitamin C. The caution applies only to vitamin C supplements and not to vitamin C found in foods.
This study was done in men, who happen to be more likely than women to develop stones. Having had a kidney stone myself, I can tell you that it is not what you want. Warn your patients, and hope that they don't suffer this possible consequence of taking too much vitamin C.
For Medicine Matters, I'm Dr. Sandra Fryhofer.
Medscape Internal Medicine © 2014 WebMD, LLC
Cite this: Can Vitamin C Cause Kidney Stones? - Medscape - May 21, 2014.