Cold trials often used at least 200 mg/day continuously; prevention benefit is small in the general population and it is not a treatment
Reviewed · Published
Vitamin C
A water-soluble vitamin used in collagen synthesis, antioxidant defense, and nonheme-iron absorption.
Established functions
- A water-soluble vitamin used in collagen synthesis, antioxidant defense, and nonheme-iron absorption.
Dietary sources
- red peppers
- kiwifruit
- broccoli
Claims and evidence
Claims that Vitamin C alone prevents or treats disease, or invariably improves health without deficiency, are unsupported.
Japanese reference amounts
- Japanese adults (age and sex as specified): Adults: 100 mg/day (RDA)
Amounts studied
- Cold trials often used at least 200 mg/day continuously; prevention benefit is small in the general population and it is not a treatment
Tolerable upper limits
- Adults: 2,000 mg/day
Forms and bioavailability
Supplement forms: ascorbic acid, mineral ascorbates
- Fractional absorption falls and urinary excretion rises above modest single doses.
Safety and interactions
Adverse effects
- diarrhea
- cramps
- and oxalate-stone risk
Medicine and nutrient interactions
- nonheme iron, aluminum antacids, some laboratory tests
Contraindications and cautions
- Avoid high doses with iron-overload disorders or a kidney-stone history.
Practical selection
- Compare Vitamin C amount per serving, form, allergens, and batch testing; prefer a single-ingredient product suited to the intended use.
Sources and review
- Dietary Reference Intakes for Japanese (2025)Ministry of Health, Labour and Welfare (Japan)
- NIH ODS vitamin fact sheetsNIH Office of Dietary Supplements
Daiki Minaki (editorial and evidence review) ·