Vitamin C Supplements and Kidney Stones: Where the Megadose Meets the Oxalate

2026-08-28 · By Marcus Reed, Content Editor · Dietary reference, not medical advice

Vitamin C has a reputation as the harmless vitamin — the one you take extra of at the first sniffle. For stone formers, the supplement form carries a specific, well-documented catch: the body converts excess ascorbic acid into oxalate, the molecule that builds the most common kidney stone. The data distinguish sharply between food vitamin C and the pill form.

The finding, plainly: A 2013 study in JAMA Internal Medicine followed 23,355 Swedish men for 11 years: those taking vitamin C supplements had a 92 percent higher risk of developing stones than non-users, and men taking more than seven tablets a week had a 123 percent higher risk — with a typical Swedish tablet containing 1,000 mg. Regular multivitamins showed no such increase. A 2016 analysis of 197,271 people across three US cohorts (Ferraro, Curhan et al., AJKD) confirmed the pattern: total and supplemental vitamin C intake at high levels raised risk in men, while dietary vitamin C from food showed no association in men or women. Small controlled trials add the mechanism: 2,000 mg/day of ascorbic acid raised urinary oxalate by about 20 percent in non-stone-formers and 33 percent in stone formers.

The Chemistry, Explained

Ascorbic acid is metabolized to oxalate — by some estimates it accounts for a meaningful share of the oxalate the body excretes each day. At food-level doses (the reference intake is 90 mg/day for men, 75 mg for women), the conversion is trivial. At supplement doses — 500, 1,000, 2,000 mg — the oxalate load grows with the dose, and it lands directly in the urine where calcium-oxalate stones form. That is why the dietary-versus-supplement split matters so much: an orange delivers vitamin C with potassium and fluid; a 1,000-mg tablet delivers a tenfold dose with nothing else.

The sex difference in the data is honest and unexplained: the Swedish study and the 2016 US analysis both found the association in men and not in women. The authors of the 2016 analysis note the finding in men is consistent and dose-responsive, while the women's cohorts showed no significant association. The practical reading for anyone with a stone history is the conservative one Curhan stated plainly: high-dose vitamin C supplements are worth avoiding, particularly with a calcium-oxalate history.

The boundary, stated clearly: this page is about supplement-dose vitamin C and stone risk; it is not a reason to cut fruit or vegetables, whose vitamin C levels showed no association with stones. People taking high-dose vitamin C for a medical reason — deficiency, certain therapies — should discuss dose with their clinician rather than stopping on their own.

The Vitamin C Shelf, Measured

Food sources versus the supplement — the oxalate-ledger view:

Food	Oxalate (mg)	Serving	Rating
Orange, fresh	2 mg	1 medium	Safe
Strawberries, fresh	8 mg	1/2 cup	Safe
Bell pepper, red, raw	3 mg	1/2 cup	Safe
Apple, fresh	2 mg	1 medium	Safe
Banana	6 mg	1 medium	Safe

The food sources of vitamin C sit comfortably low on oxalate — an orange delivers its vitamin C with about 2 mg of oxalate and a glass worth of fluid. The measured position: meet vitamin C needs from the plate, and treat the 1,000-mg tablet as the dose pattern the stone data flag. If a supplement is part of your routine, the dose question is one to raise with your doctor — especially with a stone history.

What to Do With This

Three habits cover most of the upside. Check the supplement shelf: any vitamin C product at 500 mg or more per tablet is in the dose range the data flag, and a routine multivitamin (typically 60-90 mg) is not the concern. Get vitamin C from food — the cohorts found no risk from dietary intake, and the food sources carry fluid and potassium that help the stone ledger. And if you take high-dose vitamin C for a specific reason, bring the stone history into the conversation: the dose that is right for one person may not be right for a stone former.

Frequently Asked Questions

Does vitamin C cause kidney stones?

Supplement-dose vitamin C is associated with higher stone risk in men — roughly double in the Swedish cohort — because the body converts excess ascorbate to oxalate. Food-level vitamin C showed no association with stones in either sex.

Is a daily multivitamin a problem?

No — the multivitamin dose (typically 60-90 mg) sits at the reference intake and showed no increase in stone risk. The signal in the data is at supplement doses, from around 1,000 mg per tablet upward.

Sources:
Harvard T.H. Chan School of Public Health Oxalate Database (2024); USDA FoodData Central; Harvard Health Blog: High-dose vitamin C linked to kidney stones in men (JAMA Intern Med 2013 study); Ferraro PM, Curhan GC, et al. Total, dietary, and supplemental vitamin C intake and risk of incident kidney stones. Am J Kidney Dis. 2016.; Tufts Health & Nutrition Letter: High-dose vitamin C pills could double kidney-stone risk. All oxalate values are lab-measured via ion chromatography. This page is a dietary reference tool, not medical advice.

See how oxalate values are measured and verified on our data methodology page.

Medical Disclaimer: This site is a dietary reference tool based on published food composition data. It does not provide medical advice, diagnose, or treat any condition. Talk to your doctor or a registered dietitian before changing your diet, especially if you have kidney stones, kidney disease, or other medical conditions.