Vitamin C

Ascorbic Acid · L-Ascorbic Acid

Snapshot

Indications	Contraindications
Scurvy prevention¹ Wound healing² Nonheme iron absorption¹ Common cold in extreme exposure¹ Age-related macular degeneration¹ Vitamin C inadequacy in smokers¹	Hereditary hemochromatosis¹ Recurrent kidney stones² Renal impairment or hemodialysis²

Vitamin C (L-ascorbic acid) is an essential water-soluble vitamin that humans cannot synthesize; it is required for collagen formation and acts as an antioxidant¹. It is taken to prevent or correct deficiency and scurvy, to support wound healing, and to improve nonheme iron absorption¹. People who smoke, eat a limited variety of food, or have malabsorption are most prone to inadequacy¹. It is also used for the common cold and immune function, where benefit is modest.¹

Observational and umbrella-review data link higher intake with lower cardiovascular and some cancer risk³. Large supplement trials have not shown protection against either¹. For colds, regular intake did not lower incidence in the general population but did under extreme exercise or cold exposure¹. In a 2021 open-label randomized trial of outpatients with COVID-19, high-dose ascorbic acid, alone or with zinc, did not shorten symptom duration⁴. Supplements are mostly ascorbic acid, with sodium or calcium ascorbate and bioflavonoid combinations also sold; see Form comparison¹.

Vitamin C raises nonheme iron absorption, so chronic high intake could worsen iron overload in hereditary hemochromatosis¹. Per the fact sheet, people undergoing chemotherapy or radiation should consult their oncologist before taking antioxidant supplements¹.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

95 sources, 85 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources