With all the good research done on whether or not vitamin C causes kidney stones, it is a bit surprising that the March 2013 issue of the journal Internal Medicine published a very low quality epidemiological study doing a hatchet job on vitamin C as a cause for kidney stones. The premise is that one of the five metabolites of vitamin C is oxalate, and many kidney stones are made of calcium oxalate. There are five major types of kidney stones and the type the patients in this study were unknown. Actually, vitamin C dissolves both calcium phosphate and stuvite stones and while it may slightly increase levels of oxalate, it also solubilizes calcium and oxalate, thereby preventing stone formation.
This study was not randomized and had low statistical power because there were only 31 cases of kidney stones. Previous studies using much larger doses of vitamin C were not assosiated with increased kidney stone formation.
Keep in mind that vitamin C is not totally innocuous as it can cause systemic oxalosis in people with kidney failure and can also cause a severe hemolytic crisis in people who have G6PD deficiency.
