Compound or practice · Supplement
Vitamin C
An essential antioxidant and enzyme cofactor — cures scurvy, modestly shortens colds, and triples plant-iron absorption.
- Overall grade
- Grade A
- Last revised
- 4
- graded outcomes
- 1
- reference listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
2 at grade A · 1 at grade B · 1 at grade D — 4 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Scurvy / deficiencyEvidence grade A
Definitional
Largehigh
- Non-heme iron absorptionEvidence grade A
~2–3× when taken together
Moderatehigh
- Cold durationEvidence grade B
Cochrane: modest shortening, not prevention
Smallhigh
- Cancer / CVD preventionEvidence grade D
Oral megadose trials null
Trivialhigh
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Thin evidence: Cancer / CVD prevention (grade D).
- Caution with Anticoagulants (warfarin): Gram-plus doses can swing INR; keep intake consistent.
Interactions
Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.
Anticoagulants (warfarin)Caution
Gram-plus doses can swing INR; keep intake consistent.
IronWorks together
Reduces iron to its absorbable form — take together to raise plant-iron uptake.
The evidence in words
What it is
Vitamin C is a water-soluble essential nutrient humans cannot synthesize. It is required to prevent scurvy and serves as a cofactor for collagen synthesis and several other enzymes. Whole-food sources (citrus, peppers, kiwi) easily cover requirements; supplements add margin.
How it works
Ascorbate donates electrons, regenerating other antioxidants and serving as a cofactor for prolyl and lysyl hydroxylases that stabilize collagen's triple helix — which is why deficiency causes the connective-tissue breakdown of scurvy. In the gut it reduces ferric to ferrous iron, sharply improving non-heme (plant) iron absorption.
What the evidence shows
Grade A for deficiency and for collagen-dependent roles. For the common cold, the honest read from Cochrane is that routine supplementation does not prevent colds in the general population but modestly shortens their duration, with a larger effect in people under heavy physical stress. Megadose claims for cancer and cardiovascular disease are not supported by oral trials. Its most reliably useful everyday trick is iron absorption.
How to use it
75–120 mg/day covers requirements; 200–500 mg is a common well-absorbed supplemental dose. Split doses above ~500 mg — absorption fraction falls as the dose rises. Take with a plant-iron source when the goal is iron absorption.
Safety & interactions
Very safe; excess is excreted. Very high doses can cause GI upset and, in susceptible people, raise oxalate and kidney-stone risk. High-dose vitamin C can distort some point-of-care glucose meters and, at gram doses, may affect warfarin control. Iron — Reduces iron to its absorbable form — take together to raise plant-iron uptake. warfarin — Gram-plus doses can swing INR; keep intake consistent.
Bottom line
Eat the fruit and vegetables; a 200–500 mg supplement is a reasonable, cheap margin. Best evidence-backed uses are preventing deficiency, supporting collagen, shortening colds slightly, and boosting plant-iron uptake — not curing disease.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Requirement
- 75–120 mg/day from food or supplement.
- Supplemental
- 200–500 mg/day; split larger doses.
Goes with
- IronReduces iron to its absorbable form — take together to raise plant-iron uptake.Evidence grade A
Related reading
Entries that share this one's tags or conditions.
- Vitamin C for Cancer / CVD preventionEvidence grade D — Oral megadose trials nullEvidence grade D
- Vitamin C for Cold durationEvidence grade B — Cochrane: modest shortening, not preventionEvidence grade B
- Vitamin C for Non-heme iron absorptionEvidence grade A — ~2–3× when taken togetherEvidence grade A
- Vitamin C for Scurvy / deficiencyEvidence grade A — DefinitionalEvidence grade A
Sources
As this entry records them: title, journal and year. None carries a DOI or PubMed id, so none is linked as a verified paper. Each link searches PubMed for the title; check that what you find is what the entry describes.
- 1.Vitamin C for preventing and treating the common cold (Cochrane review) — Cochrane Database Syst Rev, 2013. Search PubMed (opens in a new tab)
Last revised . A grade is this entry's reading of the evidence, not medical advice.