{"@context":"https://schema.org","@type":"DietarySupplement","id":"https://nutripedia.co.uk/items/vitamin-c","url":"https://nutripedia.co.uk/items/vitamin-c","name":"Vitamin C","category":"Vitamins","tagline":"Antioxidant powerhouse supporting immunity and collagen synthesis.","verdict":"mixed","evidenceRating":3,"verdictSummary":"Essential nutrient with clear benefits for deficiency prevention. Evidence for mega-dosing to prevent colds is weak, but may modestly reduce duration.","dosage":{"recommended":"80–200","unit":"mg","timing":"With meals","notes":"Doses above 1000 mg offer no additional benefit and may cause GI issues."},"keyBenefits":["Supports collagen production for skin and joints","Enhances immune cell function","Improves non-haem iron absorption","Potent antioxidant protecting against oxidative stress"],"warnings":["High doses (>1000 mg) may cause diarrhoea and nausea","Can increase oxalate levels — caution with kidney stone history","Most people get enough from a balanced diet"],"evidenceSummary":null,"dosing":null,"safety":null,"whoMightBenefit":[],"whoShouldAvoid":[],"regulatoryNotes":null,"faqs":[{"question":"What does the research say about vitamin C and common colds?","answer":"A 2013 Cochrane meta-analysis of 29 trials (n>11,000) found that regular vitamin C supplementation did not reduce cold incidence in the general population but modestly reduced cold duration by 8% in adults and 14% in children. In trials of soldiers and athletes under heavy physical stress, cold incidence was halved. Therapeutic dosing at cold onset showed inconsistent results across trials."},{"question":"What dosage ranges have been studied for vitamin C?","answer":"The NHS RNI for adults is 40 mg/day; EFSA has established a population reference intake of 110 mg/day for men and 95 mg/day for women. Cochrane cold trials used 200 mg to 2000 mg/day; plasma vitamin C saturates at approximately 200–400 mg/day in most healthy adults, meaning doses above this provide diminishing returns for tissue saturation. Doses above 1000 mg/day are associated with increased reported adverse events in trials."},{"question":"What side effects have been reported in vitamin C trials?","answer":"Gastrointestinal effects (diarrhoea, nausea, abdominal cramping) are the most frequently reported adverse events at doses above 1000 mg/day. EFSA and NHS note that high doses increase urinary oxalate excretion, with observational data associating supplemental doses above 1000 mg/day with higher kidney stone risk in susceptible individuals. The NHS advises not exceeding 1000 mg/day from supplements."},{"question":"Is there evidence for vitamin C use in pregnancy?","answer":"The NHS recommends 40 mg/day for pregnant women — the standard adult RNI. A 2015 Cochrane review of vitamin C supplementation in pregnancy (24 trials) found no clear benefit for pre-eclampsia, perinatal mortality, or preterm birth and concluded evidence did not support routine high-dose supplementation. EFSA has not established a separate tolerable upper intake level for pregnancy; the adult tolerable upper intake of 2000 mg/day applies."},{"question":"Which form of vitamin C has the strongest evidence base?","answer":"Ascorbic acid (the standard form) is the most extensively studied and is the reference compound in all EFSA health claim assessments. Sodium ascorbate and calcium ascorbate are buffered forms with similar bioavailability; Ester-C (calcium ascorbate with metabolites) has been marketed as superior-absorbed, but independent RCTs show no consistent advantage over standard ascorbic acid for plasma or leukocyte saturation."},{"question":"What do NHS and EFSA say about vitamin C?","answer":"EFSA has authorised health claims for vitamin C and: protection of cells from oxidative stress, collagen formation for normal function of skin/bones/cartilage/teeth/gums/blood vessels, normal immune function, reduction of tiredness and fatigue, normal iron absorption, and normal psychological function. NHS guidance confirms most adults get sufficient vitamin C through diet; high-dose supplementation beyond RNI is not recommended for healthy individuals without specific clinical indication."},{"question":"What does research say about vitamin C and skin health?","answer":"As an obligatory cofactor for collagen-synthesising enzymes, vitamin C is essential for skin structural integrity. A 2017 narrative review in Nutrients summarised RCT and mechanistic data showing that both oral and topical ascorbic acid support collagen synthesis, protect against UV-induced damage, and improve wound healing parameters. Most benefits in skin RCTs were observed in deficient or low-status populations rather than in adequately nourished individuals."}],"research":{"totalCount":14,"papers":[{"title":"Vitamin C: Health Professional Fact Sheet","year":2025,"journal":"NIH Office of Dietary Supplements","doi":null,"pmid":"","url":"https://pubmed.ncbi.nlm.nih.gov//","studyDesign":"regulatory","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C: A Comprehensive Review of Its Role in Health, Disease Prevention, and Therapeutic Potential","year":2025,"journal":"Molecules","doi":"10.3390/molecules30030748","pmid":"39942850","url":"https://doi.org/10.3390/molecules30030748","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C reduces the severity of common colds: a meta-analysis","year":2023,"journal":"BMC Public Health","doi":"10.1186/s12889-023-17229-8","pmid":"38082300","url":"https://doi.org/10.1186/s12889-023-17229-8","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Association of Vitamin C Treatment with Clinical Outcomes for COVID-19 Patients: A Systematic Review and Meta-Analysis","year":2022,"journal":"Healthcare (Basel)","doi":"10.3390/healthcare10122456","pmid":"36553979","url":"https://doi.org/10.3390/healthcare10122456","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"A Systematic Review on the Role of Vitamin C in Tissue Healing","year":2022,"journal":"Antioxidants (Basel)","doi":"10.3390/antiox11081605","pmid":"36009324","url":"https://doi.org/10.3390/antiox11081605","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C supplementation for prevention and treatment of pneumonia","year":2021,"journal":"Cochrane Database of Systematic Reviews","doi":"10.1002/14651858.CD013134.pub3","pmid":"34791642","url":"https://doi.org/10.1002/14651858.CD013134.pub3","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Evaluation and clinical comparison studies on liposomal and non-liposomal ascorbic acid (vitamin C) and their enhanced bioavailability","year":2021,"journal":"Journal of Liposome Research","doi":"10.1080/08982104.2020.1820521","pmid":"32901526","url":"https://doi.org/10.1080/08982104.2020.1820521","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"The regulation of dietary iron bioavailability by vitamin C: a systematic review and meta-analysis","year":2017,"journal":"Proceedings of the Nutrition Society","doi":"10.1017/S0029665117003445","pmid":"","url":"https://doi.org/10.1017/S0029665117003445","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C and Immune Function","year":2017,"journal":"Nutrients","doi":"10.3390/nu9111211","pmid":"29099763","url":"https://doi.org/10.3390/nu9111211","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C and Infections","year":2017,"journal":"Nutrients","doi":"10.3390/nu9040339","pmid":"28353648","url":"https://doi.org/10.3390/nu9040339","studyDesign":"systematic-review","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Scientific Opinion on Dietary Reference Values for Vitamin C","year":2013,"journal":"EFSA Journal","doi":"10.2903/j.efsa.2013.3418","pmid":"","url":"https://doi.org/10.2903/j.efsa.2013.3418","studyDesign":"regulatory","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C for preventing and treating the common cold","year":2013,"journal":"Cochrane Database of Systematic Reviews","doi":"10.1002/14651858.CD000980.pub4","pmid":"23440782","url":"https://doi.org/10.1002/14651858.CD000980.pub4","studyDesign":"meta-analysis","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C pharmacokinetics: implications for oral and intravenous use","year":2004,"journal":"Annals of Internal Medicine","doi":"10.7326/0003-4819-140-7-200404060-00010","pmid":"15068981","url":"https://doi.org/10.7326/0003-4819-140-7-200404060-00010","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0},{"title":"Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance","year":1996,"journal":"Proceedings of the National Academy of Sciences USA","doi":"10.1073/pnas.93.8.3704","pmid":"8623000","url":"https://doi.org/10.1073/pnas.93.8.3704","studyDesign":"rct","fields":[],"conclusion":"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.","abstract":"","citationCount":0}]},"machineReadable":{"markdownUrl":"https://nutripedia.co.uk/items/vitamin-c/markdown","jsonUrl":"https://nutripedia.co.uk/items/vitamin-c/json","llmsTxt":"https://nutripedia.co.uk/llms.txt"},"disclaimer":"Informational supplement research only. Not medical advice. Consult a qualified healthcare professional before taking supplements.","lastReviewed":"2026-04-20T00:00:00.000Z","updatedAt":"2026-04-20T00:00:00.000Z"}