Vitamin C
Mixed EvidenceAntioxidant powerhouse supporting immunity and collagen synthesis.
Not medical advice
Nutripedia summarises published peer-reviewed research. This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional before taking any supplement.
Vitamin C (ascorbic acid) is a water-soluble essential vitamin that functions as an antioxidant and cofactor in collagen biosynthesis, immune defence, and non-haem iron absorption. Dietary deficiency causes scurvy; subclinical inadequacy impairs wound healing and immune function. The NHS RNI is 40 mg/day for adults; EFSA population reference intake is 95–110 mg/day. Most UK adults achieve adequacy through diet; specific groups (smokers, those with malabsorption) may have higher requirements.
Essential nutrient with well-established EFSA-authorised health claims for immune function, collagen synthesis, antioxidant protection, and iron absorption. The Cochrane evidence base does not support high-dose supplementation for cold prevention in the general population, though modest duration benefits are seen. Evidence for cardiovascular and cancer benefits from supplementation in replete adults is inconsistent.
Non-haem Iron Absorption
14 studies · 520 participants
Collagen Synthesis & Wound Healing
10 studies · 680 participants
Immune Cell Function & Infection Duration
31 studies · 9,745 participants
The Evidence
14 peer-reviewed papers, updated 5 days ago
4 meta-analyses · 5 systematic reviews · 3 RCTs · 2 regulatory documents
Vitamin C: Health Professional Fact Sheet
National Institutes of Health Office of Dietary Supplements
NIH Office of Dietary Supplements
RDA for adults: 90 mg/day (men), 75 mg/day (women); smokers add 35 mg/day. Tolerable Upper Intake Level: 2,000 mg/day for adults. Cell saturation occurs at ~100 mg/day; plasma increases only marginally above 200 mg/day. High doses may cause gastrointestinal disturbance. Vitamin C is essential for collagen synthesis, immune function, and iron absorption.
Vitamin C: A Comprehensive Review of Its Role in Health, Disease Prevention, and Therapeutic Potential
Alberts A, Moldoveanu ET, Niculescu AG et al.
Molecules
Vitamin C functions as a cofactor in collagen and hormone synthesis and is involved in immunity, iron absorption, and antioxidant processes. Pharmacological-dose IV administration shows promise in cancer and sepsis. Contradictory findings in oral supplementation trials highlight the need for larger, longer-duration studies across chronic disease indications.
Vitamin C reduces the severity of common colds: a meta-analysis
Hemilä H, Chalker E
BMC Public Health
Analysis of 15 comparisons from 10 double-blind RCTs found vitamin C supplementation reduced common cold severity by 15% compared to placebo. Effects were more pronounced for severe symptom presentations than mild cases, with clinical relevance for work and school absenteeism.
Association of Vitamin C Treatment with Clinical Outcomes for COVID-19 Patients: A Systematic Review and Meta-Analysis
Huang WY, Hong J, Ahn SI et al.
Healthcare (Basel)
Meta-analysis of 19 studies (949 vitamin C recipients, 1,816 controls) found a trend toward lower COVID-19 mortality (RR 0.81, 95% CI 0.62–1.07) that did not reach statistical significance. No significant differences in ventilation incidence, hospitalisation duration, or ICU stay. Larger trials are needed.
A Systematic Review on the Role of Vitamin C in Tissue Healing
Bechara N, Flood VM, Gunton JE
Antioxidants (Basel)
Vitamin C supplementation improved wound healing outcomes, predominantly for pressure ulcers, acting as a cofactor for prolyl and lysyl hydroxylases essential in collagen triple-helix formation and as an antioxidant reducing ROS-driven cell apoptosis during inflammation. Evidence quality was limited by small samples and multi-nutrient designs.
Vitamin C supplementation for prevention and treatment of pneumonia
Padhani ZA, Moazzam Z, Ashraf A et al.
Cochrane Database of Systematic Reviews
Five studies (2,655 participants) were insufficient to determine whether vitamin C prevents or treats pneumonia. Evidence certainty rated very low due to small sample sizes and high risk of bias. Further high-quality RCTs are required before clinical recommendations can be made.
Evaluation and clinical comparison studies on liposomal and non-liposomal ascorbic acid (vitamin C) and their enhanced bioavailability
Gopi S, Balakrishnan P
Journal of Liposome Research
Liposomal oral vitamin C was 1.77 times more bioavailable than standard oral ascorbic acid, with particle sizes below 100 nm and 65.85% encapsulation efficiency. Liposomal delivery produced measurably higher peak plasma concentrations and total exposure, enabling meaningful increases in systemic vitamin C without exceeding gastrointestinal tolerance.
The regulation of dietary iron bioavailability by vitamin C: a systematic review and meta-analysis
Heffernan A, Evans C, Holmes M et al.
Proceedings of the Nutrition Society
Meta-analysis of short-term studies (n=315) demonstrated highly significant increases in non-haem iron absorption when ascorbic acid was co-ingested with test meals. Long-term supplementation (5 studies, n=118) also significantly raised haemoglobin. Authors conclude increasing vitamin C intake is a practical strategy to reduce iron deficiency risk.
Vitamin C and Immune Function
Carr AC, Maggini S
Nutrients
Vitamin C accumulates in neutrophils and macrophages, supports epithelial barrier integrity, promotes phagocytosis and reactive oxygen species generation, and facilitates lymphocyte differentiation. Prophylactic benefit requires 100–200 mg/day; treatment of established infections may require gram-level doses. Deficiency compromises immune competence.
Vitamin C and Infections
Hemilä H
Nutrients
Vitamin C halved cold incidence in physically active people and shortened duration in the general population. Three controlled trials showed prevention of pneumonia; two showed treatment benefit. A dose-response was seen at 6–8 g/day for cold duration. 148 animal studies support broader anti-infective properties.
Scientific Opinion on Dietary Reference Values for Vitamin C
EFSA Panel on Dietetic Products Nutrition and Allergies (NDA)
EFSA Journal
EFSA established Population Reference Intakes (PRIs) of 110 mg/day for adult men and 95 mg/day for adult women, targeting plasma near-saturation at ~50 µmol/L. No tolerable upper intake level was set due to insufficient evidence of adverse effects at high intakes. Smokers require higher intakes to achieve equivalent plasma levels.
Vitamin C for preventing and treating the common cold
Hemilä H, Chalker E
Cochrane Database of Systematic Reviews
Regular vitamin C supplementation (≥200 mg/day) does not reduce cold incidence in the general population but modestly reduces duration (8% in adults, 14% in children). In athletes under extreme physical stress, vitamin C halved cold risk. Therapeutic dosing after symptom onset showed no consistent benefit.
Vitamin C pharmacokinetics: implications for oral and intravenous use
Padayatty SJ, Sun H, Wang Y et al.
Annals of Internal Medicine
Oral vitamin C is tightly controlled by intestinal absorption and renal reabsorption; a 1.25 g oral dose achieved peak plasma of ~135 µmol/L versus ~885 µmol/L intravenously. Only intravenous administration produces pharmacological concentrations potentially relevant to antitumour activity. Prior oral-only cancer trials were therefore pharmacologically inadequate.
Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance
Levine M, Conry-Cantilena C, Wang Y et al.
Proceedings of the National Academy of Sciences USA
Vitamin C exhibits sigmoid pharmacokinetics: plasma becomes fully saturated at 1,000 mg/day. Bioavailability is near complete at doses up to 200 mg but decreases at higher intakes. The authors recommended raising the RDA to 200 mg/day, achievable through diet. Safe daily dose defined as below 1,000 mg.
Evidence Database
Click any row to explore the studies behind each health outcome. Grades reflect the volume and quality of published research, not a recommendation.
| Grade | Health Outcome | |
|---|---|---|
| A | Non-haem Iron Absorption14 studies | |
| A | Collagen Synthesis & Wound Healing10 studies | |
| B | Immune Cell Function & Infection Duration31 studies | |
| B | Oxidative Stress & Antioxidant Status22 studies | |
| C | Blood Pressure8 studies |
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General Information
Dosage (Evidence-Reported)
These figures reflect what clinical studies used — not personalised recommendations.
Safety Notes
- Doses above 1000 mg/day commonly reported to cause GI adverse events (diarrhoea, nausea)
- High-dose supplementation increases urinary oxalate — caution with history of kidney stones
- Cochrane evidence does not support cold prevention in general population
- Most healthy UK adults achieve adequacy through diet alone
Key Benefits
- Essential cofactor for collagen synthesis — bone, skin, gum, blood vessel integrity
- Enhances non-haem iron absorption up to 4-fold when co-ingested
- Potent aqueous antioxidant — regenerates vitamin E
- Reduces cold duration modestly in clinical trial data (8% adults, 14% children)
- Supports immune cell function; EFSA-authorised claim
Quick Facts
Legal food supplement (UK). Multiple EFSA-authorised health claims for immune function, collagen formation, antioxidant protection, iron absorption, energy metabolism, and reduction of tiredness and fatigue.
Frequently Asked Questions
Nutripedia is an educational resource. Content is sourced from peer-reviewed studies and does not constitute medical advice. Consult a healthcare professional before starting any supplement.