Supplement

Vitamin C

Also known as Ascorbic Acid

Water-soluble antioxidant vitamin and essential cofactor for collagen synthesis and non-haem iron absorption; supports immune cell function and skin integrity, and cannot be made by the human body.

2linked conditions

20linked studies

On this pageEvidence Availability Outcomes & conditions →

Evidence

What the research actually shows

We link to relevant studies and leave interpretation to you and your healthcare professional.

Evidence analytics

Where the evidence is concentrated

Number of audited published findings for Vitamin C by condition. Drill into a pair page for the full breakdown.

Putative uses

Where people report using it and what trials suggest

Strong evidenceScurf prevention / deficiency
Moderate evidenceCold duration modestly shortened (~8%) in adults
Moderate evidenceCold incidence reduced only in extreme physical stress (marathon/skiing)

Where the evidence is negative

Common claims the trials do not support

Does not prevent colds in the general population.
No mortality/CVD benefit in large supplement trials.
Sepsis, cancer, and COVID outpatient evidence inconclusive.

Essential vitamin; deficiency correction is definitive, but popular cold and disease-prevention uses are weak.

Safety notes: GI upset and oxalate/kidney-stone risk at megadoses (>1-2 g/day).

Evidence grades reflect study quality and consistency, not marketing claims.

20studies referenced

13journals

2005–2026publication range

01Surviving Sepsis Campaign International Guidelines for the Management of Sepsis and Septic Shock in Children 2026Weiss SL, et al. · Pediatric critical care medicine : a journal of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies · 2026PMID 41869844 ↗02Surviving Sepsis Campaign International Guidelines for the Management of Sepsis and Septic Shock in Children 2026Weiss SL, et al. · Intensive care medicine · 2026PMID 41870559 ↗03Clinical benefits and risks of high-dose intravenous vitamin C: a systematic reviewAlangari A, et al. · Journal of medicine and life · 2026PMID 41815850 ↗04Application of Antioxidant Mixture Prevents Cutaneous "Oxinflammaging" in Subjects Exposed to Particulate MatterIvarsson J, et al. · Journal of cosmetic dermatology · 2025PMID 40642809 ↗05Granulomatous Reactions From Microneedling: A Systematic Review of the LiteratureFriedmann DP, et al. · Dermatologic surgery : official publication for American Society for Dermatologic Surgery [et al.] · 2025PMID 39584690 ↗06Therapeutic effects of high-dose vitamin C supplementation in patients with COVID-19: a meta-analysis

Search PubMed ↗Find clinical trials ↗

What trials found, in numbers

Summaries of published trial results for this compound, grouped by condition. Numbers are reported exactly as the researchers published them — we never calculate or convert.

How to read this table

Benefit: What the trial saw happen: whether the measured outcome moved in the helpful direction in that one study (the tag on each row: “Benefit seen”, “No clear benefit” or “Unclear”). It is a study result — not advice, and not a promise it will work for you.
Evidence: How strong the research behind that result is. A meta-analysis pools many studies (strongest); a systematic review collates them; an RCT tests against a control (placebo); observational studies only watch — they can suggest, not prove.
Effect size: How large the measured change was, exactly as the researchers published it. “No number reported” means the abstract gave no effect size — we never invent one.

In short: benefit is what was observed; evidence is how much you should trust the observation. A “Benefit seen” tag on a weak study counts for far less than the same tag on a meta-analysis.

Immune Support (3 outcomes)

Outcome measured	What trials found	Effect size	People studied	Duration	Type of evidence	Study
duration of respiratory infection	Vitamin C significantly shortened infection duration compared to placebo (SMD -0.36, P=0.01). (95% CI -0.62 to -0.09, P = 0.01)Benefit seen	-0.36	—	—	Meta-analysis · 2022	PMID 34967304
incidence of respiratory illness	Vitamin C showed no significant benefit in preventing respiratory illness compared to placebo (RR 0.94, P=0.09). (95% confidence interval of 0.87 to 1.01, P= 0.09)No clear benefit	0.94	—	—	Meta-analysis · 2022	PMID 34967304

Outcomes & conditions

Why people look into Vitamin C — and what they report

Associated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.

Outcomes & conditions →

Important: This page reflects observational, aggregate-only community reporting and independent published research. It is not medical advice, and it does not claim any compound treats, cures, or is effective for any condition. Always consult a qualified healthcare professional before starting, stopping, or changing any supplement or treatment.

Availability

Where to get Vitamin C (UK)

How this compound is sold in the UK, and where our readers typically find it.

Retailer search links — we may earn commission on purchases at no cost to you. Commission never affects our evidence ratings.

Search Vitamin C on Amazon UK →Search Vitamin C on Holland & Barrett →Search Vitamin C on iHerb →

Outcome measured	What trials found	Effect size	People studied	Duration	Type of evidence	Study
Photodamage improvement with topical ascorbic acid	Topical ascorbic acid improved photodamage compared to placebo in a small study; the abstract gives no effect size.Benefit seen	no number reported	—	—	Meta-analysis · 2005	PMID 15674885
Photodamage improvement with tretinoin	Tretinoin cream increased the chance of photodamage improvement compared to placebo, with a relative risk of 1.73 at 24 weeks. (95% confidence interval 1.39 to 2.14)Benefit seen	1.73 relative risk	—	24 weeks	Meta-analysis · 2005	PMID 15674885
Wrinkle score after laser treatment	Carbon dioxide laser treatment did not improve wrinkle scores more than dermabrasion, compared at 4 to 6 months.No clear benefit	no number reported	—	4 to 6 months	Meta-analysis · 2005	PMID 15674885