Quick answer
NIH says high vitamin C intakes could add to kidney stones by raising urinary oxalate and uric acid, but studies conflict and the best evidence is in people who already pass too much oxalate. One cohort found 19% more stones in men taking 1,000 mg or more a day from supplements, but not in women.1,2
Key facts
- NIH says high vitamin C intakes can raise urinary oxalate and uric acid, which could contribute to kidney stones, especially in people with kidney problems.1
- Studies of 30 mg to 10 g a day on urinary oxalate had conflicting results, so NIH calls it unclear whether vitamin C plays a role.1
- In three large cohorts, 1,000 mg or more a day from supplements went with 19% higher stone risk in men, and no significant link in women.2
- Vitamin C from food was not linked to stones in that study, though few people ate more than 700 mg a day from food.2
- MedlinePlus says amounts above 2,000 mg a day can cause stomach upset and diarrhea and, rarely, kidney stones.3
What NIH says about vitamin C and kidney stones
NIH's fact sheet for health professionals explains the concern: high vitamin C intakes have the potential to increase urinary oxalate and uric acid, which could contribute to kidney stones, especially in people with kidney disease. It then says that studies of intakes from 30 mg to 10 g a day on urinary oxalate gave conflicting results, so it is not clear whether vitamin C plays a role. The best evidence it names is in patients who already pass too much oxalate.1
High intakes raise the oxalate and uric acid passed in urine, which could add to kidney stones, especially in people with kidney problems. Studies conflict, and NIH says the best evidence of a link is in people who already pass too much oxalate.1,4
MedlinePlus says that amounts above 2,000 mg a day, which it does not recommend, can cause stomach upset and diarrhea and, although rarely, kidney stones.3
What did the large cohort study find?
Researchers followed 156,735 women and 40,536 men in three large health studies for about 11 years, during which 6,245 kidney stones were identified. In men, total vitamin C of 1,000 mg or more a day went with 43% higher risk of stones than under 90 mg a day (hazard ratio 1.43, 1.15 to 1.79), and 1,000 mg or more from supplements went with 19% higher risk (1.19, 1.01 to 1.40). In women the links were not significant.2
Vitamin C from food was not linked to stones in men or women, although few people ate more than 700 mg a day from food. The authors listed limits: intakes came from food questionnaires, and stone type was not known for every case. A cohort study shows an association, not cause.2
What is not known about vitamin C and kidney stones
The sources checked do not say how much vitamin C, over what time, is needed to raise the risk in a person with no history of stones, and they do not explain the difference between men and women in the cohort. NIH says concerns such as kidney stones are not generally considered a risk in healthy individuals.1,2
NIH's upper limit of 2,000 mg a day for adults counts vitamin C from all sources, and it is set from the risk of adverse effects of long-term high intakes.1
Does vitamin C cause diarrhea, acid reflux or breakouts?
NIH says the most common complaints at high doses are diarrhea, nausea, abdominal cramps and other gut upset, from vitamin C that is not absorbed drawing water into the gut. Acid reflux is not named in the sources checked, and neither are constipation, acne, purging, breakouts or insomnia, which is not a finding either way.1,5
High doses can cause diarrhea, nausea, stomach cramps and other gut upset, because vitamin C that is not absorbed draws water into the gut.1,5
Who should ask a doctor about vitamin C and kidney stones
- Anyone who has had kidney stones or has kidney disease, who should ask their doctor before taking vitamin C supplements.1
- Anyone who passes too much oxalate in urine, which is where NIH says the best evidence of a link lies.1
- Anyone with hemochromatosis or another cause of iron overload, who NIH says should avoid vitamin C supplements.1
Questions people ask
Does vitamin C cause kidney stones?
NIH says high intakes could contribute to kidney stones, but that studies conflict and the best evidence is in people who already pass too much oxalate. One cohort found a higher risk in men taking 1,000 mg or more a day from supplements.1,2
Does vitamin C cause diarrhea?
NIH says high doses can cause diarrhea, nausea, stomach cramps and other gut upset, because unabsorbed vitamin C draws water into the gut.1,5
Does vitamin C cause acid reflux?
The sources checked do not name acid reflux. NIH lists nausea, stomach cramps and other gut upset at high doses. Ask your doctor or pharmacist.1
Does vitamin C cause acne, purging, breakouts, constipation or insomnia?
The sources checked do not address these effects, which is not a finding either way. Ask your doctor or pharmacist if a symptom follows a new supplement.1
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Sources
- National Institutes of Health, Office of Dietary Supplements. Vitamin C: Fact Sheet for Health Professionals. Updated July 31, 2025. Opened 2026-10-07.
- Ferraro PM, Curhan GC, Gambaro G, Taylor EN. Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones. Am J Kidney Dis. 2016;67(3):400-7. A prospective cohort study. Opened 2026-10-11.
- MedlinePlus Medical Encyclopedia. Vitamin C. U.S. National Library of Medicine. Review date 1/21/2025. Opened 2026-10-11.
- Levine M, Conry-Cantilena C, Wang Y, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci U S A. 1996;93(8):3704-3709. Opened 2026-10-07.
- Office of Dietary Supplements, National Institutes of Health. Vitamin C: Fact Sheet for Consumers. Updated March 22, 2021. Opened 2026-10-07.
This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.