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Vitamin C — The Complete Supplement Guide

Antioxidant, collagen-builder and iron-absorption booster — with a saturable absorption that makes megadoses pointless. Forms, doses and limits.

Reviewed by Bodil Isaksson, Licensed Biomedical Scientist (Sweden) Last reviewed July 2026

SupplementsVitaminsVitamin CWater-soluble

A water-soluble vitamin the body can’t store — take in more than you need and the surplus is simply excreted, so there’s little to gain from mega-doses. For the short dietary version, see the Vitamins page.

Read first. Vitamin C is generally very safe, but gram-level doses cause diarrhoea and may raise kidney-stone risk in susceptible people. Absorption is saturable, so megadoses mostly end up in your urine. Information, not a prescription.

Key takeaways

  • The body can’t store it and excess is excreted, so mega-doses add little.
  • Adults need ≈ 75–110 mg/day (100–200 mg covers most).
  • Upper limit 2,000 mg/day — more can upset the stomach.

Function

Vitamin C is a multi-tasking water-soluble vitamin:

  • Collagen synthesis: essential to build collagen for skin, blood vessels, gums, bone and wound healing.
  • Antioxidant: the main antioxidant in the watery parts of the body; also regenerates vitamin E.
  • Iron absorption: converts plant (non-heme) iron to an absorbable form — take with iron-rich meals.
  • Immune function: supports immune cells and skin barriers.
  • Neurotransmitters & hormones: a cofactor in making noradrenaline and other signalling molecules.

Different forms — and which to choose

Ascorbic acidThe standard, well-absorbed and cheapest form.
Buffered (mineral ascorbates)Sodium/calcium/magnesium ascorbate — gentler on a sensitive stomach.
Liposomal / Ester-CMarketed for better absorption/tolerance; modest real-world advantage, higher price.

Absorption in the body

How muchHigh at low doses (~70–90%) but saturable — the percentage absorbed falls sharply above ~200 mg, and the surplus is excreted in urine.
TipSplit intake across the day rather than one big dose; take with iron-rich meals to boost iron absorption.

Deficiency symptoms

SymptomsScurvy — bleeding and swollen gums, slow wound healing, easy bruising, fatigue, loose teeth.
Who's at riskVery low fruit/vegetable intake, smokers (needs are higher), heavy drinkers and some restrictive diets.

Recommended intake

Adults ≈ 75–110 mg/day (+35 smokers)

Reference intakes:

  • Women: ~75–95 mg/day · Men: ~90–110 mg/day · Smokers: +35 mg/day

Best sources: citrus, berries, kiwi, peppers, broccoli, tomatoes, potatoes — fragile, so lost to heat and long storage.12

Therapeutic use

Scurvy & ironTreats and prevents scurvy; taken with meals to raise iron absorption in iron-deficiency.
ColdsModestly shortens (does not prevent) the common cold with regular intake; high-dose "at first sign" evidence is weak.

Therapeutic doses

Everyday: 100–200 mg covers most
Practical100–200 mg/day fully saturates the body's stores; more offers little extra.
MegadosesGram-level doses cause loose stools; high-dose IV vitamin C is an unproven research area, not a home therapy.

Toxicity & upper limit

UL: 2,000 mg/day
Upper limit2,000 mg/day for adults.1
ExcessDiarrhoea and stomach upset; higher kidney-stone risk in susceptible people.

Bottom line: a few servings of fruit and vegetables cover vitamin C easily. If you supplement, 100–200 mg/day is plenty — absorption is saturable, so megadoses just make expensive urine (and can upset your stomach).

← All supplementsShort dietary version

References

Reference and upper-limit values are general adult figures from official bodies; individual needs vary. Therapeutic doses describe clinical/research use, not prescriptions.

  1. US NIH Office of Dietary Supplements. Vitamin C — Health Professional Fact Sheet (function, forms, intakes, food sources, deficiency, therapeutic uses, upper limit, interactions). ods.od.nih.gov
  2. EFSA. Dietary Reference Values & Tolerable Upper Intake Levels for vitamins (European reference intakes and ULs). efsa.europa.eu

This article summarizes nutrition science from official health authorities and peer-reviewed sources for education. It is not a substitute for individual medical advice, and the doses given are not prescriptions — always consult a professional before therapeutic supplement use, in pregnancy, or alongside medication.

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