Vitamin C: Intake, Upper Limit & Side Effects

Vitamin C: Intake, Upper Limit, and Stomach Side Effects

Supplement Science Editorial Team·Evidence-Based Supplement Research

Published May 23, 2026

This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Adults need 90 mg of vitamin C per day (men) or 75 mg (women), and people who smoke need 35 mg more.

Key Takeaways

Adults need 90 mg (men) or 75 mg (women) of vitamin C daily; people who smoke need 35 mg more.
The upper limit is 2,000 mg/day; above it, the main effect is GI upset (diarrhea, nausea, cramps).
Vitamin C is water-soluble — once tissues are saturated, megadoses are largely excreted, not stored.
Very high intakes may raise kidney-stone risk mainly in people already prone to them.
People with hereditary hemochromatosis should be cautious, since vitamin C increases iron absorption.

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How Much Vitamin C Adults Need

The NIH Office of Dietary Supplements sets the vitamin C RDA at 90 mg/day for men and 75 mg/day for women, and notes that 'individuals who smoke require 35 mg/day more vitamin C than people who do not smoke' [1]. These modest amounts are easily met by fruits and vegetables — citrus, berries, peppers, broccoli, and more.

The Upper Limit and Why 'More' Backfires

The Tolerable Upper Intake Level is 2,000 mg/day [1] (see Upper Intake Levels). Vitamin C is water-soluble: once your tissues are saturated, the body absorbs a smaller fraction of large doses and excretes the rest. So megadoses don't build up reserves — they mostly pass through.

Stomach Side Effects

The most common problem with high doses is digestive. Per NIH, 'the most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances' [1]. These effects are dose-related and usually resolve when intake drops.

Kidney Stones and Iron Overload — the Caveats

Kidney stones: High intakes can raise urinary oxalate, and NIH notes the clearest risk is 'in patients with pre-existing hyperoxaluria' [1] — those already prone to stones. Evidence in the general population is mixed.
Iron overload: Vitamin C boosts iron absorption, so in people with hereditary hemochromatosis, chronic high doses 'could exacerbate iron overload' [1]. This doesn't apply to healthy people.

Practical Guidance

Aim for the RDA from food; a typical varied diet covers it.
If you supplement, there's little reason to exceed a few hundred milligrams; staying under 2,000 mg/day avoids GI upset.
People prone to kidney stones or with iron-overload conditions should be cautious with high-dose vitamin C.

Related Supplements

Vitamin C

Frequently Asked Questions

Can you take too much vitamin C?

Yes, in the sense that doses above the 2,000 mg/day upper limit commonly cause diarrhea, nausea, and stomach cramps. Vitamin C is water-soluble, so excess is mostly excreted rather than stored — meaning very high doses tend to cause GI upset without added benefit.

Does vitamin C cause kidney stones?

For most people the evidence is mixed. NIH notes the clearest risk is in people who already have a tendency to form stones (pre-existing hyperoxaluria), because high vitamin C can raise urinary oxalate. If you're prone to kidney stones, be cautious with high-dose vitamin C.

How much vitamin C should I take?

Aim for the RDA — 90 mg for men, 75 mg for women, plus 35 mg if you smoke — which a varied diet of fruits and vegetables easily provides. If you supplement, there's little reason to go far above a few hundred milligrams, and staying under 2,000 mg/day avoids stomach upset.

Who should avoid high-dose vitamin C?

People prone to kidney stones and those with hereditary hemochromatosis (an iron-overload condition), since vitamin C increases iron absorption. For healthy people, the main downside of high doses is digestive discomfort rather than a serious risk.

References

National Institutes of Health, Office of Dietary Supplements (2024). Vitamin C: Health Professional Fact Sheet. NIH Office of Dietary Supplements.