Vitamin C (Ascorbic Acid)
Also known as: Ascorbic Acid, L-Ascorbic Acid, L-ascorbate
Vitamin C is a potent antioxidant and a crucial cofactor for several enzymatic reactions, including those involved in collagen biosynthesis, carnitine synthesis, and neurotransmitter synthesis. It plays a significant role in immune health by supporting various cellular functions of both the innate and adaptive immune systems. Its antioxidant properties help protect cells from oxidative damage caused by free radicals. While widely used for common cold prevention and treatment, evidence suggests it may reduce duration and severity but not necessarily prevent illness in the general population, with more pronounced effects in individuals under severe physical stress.
Last reviewed: 2026-04-22 · 4 indexed studies
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Overview
Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is essential for numerous physiological functions, including immune system functioning, collagen synthesis, and antioxidant protection. Humans, unlike most animals, are unable to synthesize vitamin C endogenously due to the absence of the enzyme gulonolactone oxidase. Therefore, it must be obtained through diet or supplementation.
Mechanism & Function
L-Ascorbic acid · C₆H₈O₆ — source: PubChem CID 54670067
White crystalline water-soluble vitamin. Tart; oxidises quickly when wet.
- Powder
- Capsule
- Tablet
- Liquid
- RTD
Powder is generally preferred for bioavailability or efficacy.
Mechanism of Action
Vitamin C acts as a powerful reducing agent, donating electrons to neutralize free radicals and reactive oxygen species, thereby preventing oxidative damage to macromolecules. It is a necessary cofactor for dioxygenase enzymes involved in collagen hydroxylation (prolyl and lysyl hydroxylases), which is critical for collagen stability and strength. It also regenerates other antioxidants, such as vitamin E, by reducing their oxidized forms. In the immune system, it enhances neutrophil chemotaxis, phagocytosis, and modulates cytokine production.
Physiological Role
Vitamin C is indispensable for collagen formation, a major component of connective tissues, bones, blood vessels, and skin. It is involved in the biosynthesis of L-carnitine, critical for fatty acid metabolism, and several neurotransmitters. As an antioxidant, it provides protection against oxidative stress-induced cellular damage. It also facilitates the absorption of non-heme iron in the gut by reducing ferric iron to ferrous iron.
Primary Pathways
Performance / Health Relevance
For athletes and individuals undergoing intense physical stress, vitamin C supplementation may help reduce the incidence and duration of the common cold, potentially mitigating training interruptions. Its role in collagen synthesis is vital for connective tissue integrity, which is important for injury prevention and recovery. As an antioxidant, it may help counteract exercise-induced oxidative stress, though high doses immediately post-exercise might blunt some beneficial adaptive responses.
Evidence Review
Compare Vitamin C Forms
Full comparison2 vitamin c forms are indexed. Bioavailability, clinical evidence, and best-use cases differ meaningfully between them.
| Form | Evidence |
|---|---|
Vitamin C (Ascorbic Acid)This page Bioavailability decreases with increasing dose; approximately 70-90% for doses between 30-180 mg, dropping to less than 50% for doses >1 gram. Saturation occurs at plasma concentrations around 70-80 µmol/L. | 70/100 |
| Liposomal Vitamin C Improved bioavailability compared to standard ascorbic acid, particularly at higher doses, due to liposomal encapsulation protecting against degradation and facilitating absorption. Specific improvements vary by formulation. | 60/100 |
Practical Use & Dosage
- Minimum Effective Dose
- 100 mg/day (for preventing deficiency)
- Optimal Range
- 200-2000 mg/day
- Upper / Caution Level
- 2000 mg/day
- Timing
- Can be taken any time of day, with or without food. Dividing doses may improve absorption.
- Best Format
- Ascorbic acid (tablet, capsule, powder). Liposomal forms may offer enhanced bioavailability.
- Bioavailability
- Bioavailability decreases with increasing dose; approximately 70-90% for doses between 30-180 mg, dropping to less than 50% for doses >1 gram. Saturation occurs at plasma concentrations around 70-80 µmol/L.
- Absorption Considerations
- Absorbed in the small intestine via sodium-dependent vitamin C transporters (SVCTs). Bioflavonoids may enhance absorption slightly, but evidence is mixed.
Safety & Interactions
Side Effects
- •Diarrhea
- •Nausea
- •Abdominal cramps
- •Heartburn
Contraindications
- Hemochromatosis (due to enhanced iron absorption)
- Kidney stones (history of or predisposition at high doses)
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency
Drug Interactions
- •Chemotherapy agents (potential interaction with antioxidant effects, consult oncologist)
- •Estrogen (may enhance estrogen levels)
- •Warfarin (large doses may potentially interfere with anticoagulant effect)
- •Statins (potential theoretical interaction with antioxidant effects but clinical relevance unclear)
- •Aluminum-containing antacids (increases aluminum absorption)
Who Should Avoid
- •Individuals with kidney disease or a history of kidney stones.
- •Those with iron overload conditions like hemochromatosis.
- •Individuals on chemotherapy unless approved by an oncologist.
Monitoring
For high dose intake (e.g., >2 g/day), individuals prone to kidney stones should monitor urine oxalate levels. Individuals with hemochromatosis or other iron overload disorders should avoid supplemental vitamin C.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Vitamin C (Ascorbic Acid) typically used or indicated?
Vitamin C (Ascorbic Acid) is most commonly used for: Immune Support, Antioxidant, Collagen Synthesis, Skin Health, Iron Absorption. Vitamin C is indispensable for collagen formation, a major component of connective tissues, bones, blood vessels, and skin. It is involved in the biosynthesis of L-carnitine, critical for fatty acid metabolism, and several neurotransmitters. As an antioxidant, it provides protection against oxidative stress-induced cellular damage. It also facilitates the absorption of non-heme iron in the gut by reducing ferric iron to ferrous iron.
How does Vitamin C (Ascorbic Acid) work?
Vitamin C acts as a powerful reducing agent, donating electrons to neutralize free radicals and reactive oxygen species, thereby preventing oxidative damage to macromolecules. It is a necessary cofactor for dioxygenase enzymes involved in collagen hydroxylation (prolyl and lysyl hydroxylases), which is critical for collagen stability and strength. It also regenerates other antioxidants, such as vitamin E, by reducing their oxidized forms. In the immune system, it enhances neutrophil chemotaxis, phagocytosis, and modulates cytokine production.
What is the recommended dose of Vitamin C (Ascorbic Acid)?
The optimal range is 200-2000 mg/day. with a minimum effective dose of 100 mg/day (for preventing deficiency). Best taken: Can be taken any time of day, with or without food. Dividing doses may improve absorption.. Upper / caution level: 2000 mg/day.
What are the side effects of Vitamin C (Ascorbic Acid)?
Reported side effects include: Diarrhea; Nausea; Abdominal cramps; and Heartburn. Monitoring: For high dose intake (e.g., >2 g/day), individuals prone to kidney stones should monitor urine oxalate levels. Individuals with hemochromatosis or other iron overload disorders should avoid supplemental vitamin C.
Does Vitamin C (Ascorbic Acid) interact with medications?
Known or theoretical interactions: Chemotherapy agents (potential interaction with antioxidant effects, consult oncologist); Estrogen (may enhance estrogen levels); Warfarin (large doses may potentially interfere with anticoagulant effect); Statins (potential theoretical interaction with antioxidant effects but clinical relevance unclear); and Aluminum-containing antacids (increases aluminum absorption). Always check with a clinician before combining with prescription medication.
Who should avoid Vitamin C (Ascorbic Acid)?
Vitamin C (Ascorbic Acid) is generally not recommended for: Individuals with kidney disease or a history of kidney stones.; Those with iron overload conditions like hemochromatosis.; Individuals on chemotherapy unless approved by an oncologist.; Hemochromatosis (due to enhanced iron absorption); Kidney stones (history of or predisposition at high doses); and Glucose-6-phosphate dehydrogenase (G6PD) deficiency.
How strong is the evidence for Vitamin C (Ascorbic Acid)?
Evidence level: Moderate (overall score 70/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
Vitamin C and Infections.
This systematic review examined the role of vitamin C in preventing and treating infections. It highlighted vitamin C's involvement in immune function and its potential to reduce the duration and severity of the common cold, especially in physically stressed individuals.
Vitamin C: an antioxidant master that enhances iron absorption.
This review discusses the antioxidant properties of vitamin C and its crucial role in enhancing the absorption of non-heme iron, highlighting its biochemical mechanisms.
Vitamin C supplementation and the effects on oxidative stress and immune function in athletes: a systematic review.
This systematic review evaluated the impact of vitamin C supplementation on oxidative stress and immune responses in athletic populations, synthesizing findings from multiple studies.
The effect of vitamin C on the common cold. A review by the Department of General Practice, University of Helsinki.
An early meta-analysis examining the efficacy of vitamin C in preventing and treating the common cold, pooling data from numerous controlled trials.
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Research Overview
Moderate EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/vitamin-c-ascorbic-acid
SuppIndex. (2026). Vitamin C (Ascorbic Acid): Evidence summary, dosage and clinical studies. Retrieved October 23, 2026, from https://thesuppindex.com/ingredients/vitamin-c-ascorbic-acid
Based on 4 indexed studies · Evidence level: Moderate.
Goal Ratings
Stack Compatibility
Generally well-tolerated with most supplements. Can be synergistic with iron for enhanced absorption, and with other antioxidants like vitamin E for regenerative effects.