And here is a study which shows not only does vitamin C NOT cause kidney stones, those in the study that had higher doses of vitamin C actually had LESS incidence of kidney stones than those with LOWER doses of vitamin C!
No Contribution of Ascorbic Acid to Renal Calcium Oxalate Stones
Vitamin Research Department, F. Hoffmann-La Roche Ltd., Basel, Switzerland
Address of Corresponding Author
Ann Nutr Metab 1997;41:269-282 (DOI: 10.1159/000177954)
Even though a certain part of oxalate in the urine derives from metabolized ascorbic acid (AA), the intake of high doses of vitamin C does not increase the risk of calcium oxalate kidney stones due to physiological regulatory factor: gastrointestinal absorption as well as renal tubular reabsorption of AA are saturable processes, and the metabolic transformation of AA to oxalate is limited as well. Older assays for urinary oxalate favored in vitro conversion of AA to oxalate during storage and processing of the samples. Recurrent stone formers and patients with renal failure who have a defect in AA or oxalate metabolism should restrict daily vitamin C intakes to -100 mg. But in the large-scale Harvard Prospective Health Professional Follow-Up Study, those groups in the highest quintile of vitamin C intake (> 1,500 mg/day) had a lower risk of kidney stones than the groups in the lowest quintiles.