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Vitamin

Vitamin C

Vitamin C, or ascorbic acid, is an essential water-soluble vitamin that humans cannot make, found in fruits and vegetables such as citrus, peppers and berries.

Also listed as Ascorbic Acid, Ascorbate, L-ascorbic acid

Essential HealthLongevityImmune SupportCardiovascularHair & Skin

What it is studied for

The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.

Essential HealthModerateA3 studies
Oxidative stressLongevityModerateBNo linked study
Immune responseImmune SupportSmallB2 studies
Cholesterol balanceCardiovascularSmallB1 study
Immune SupportSmallBNo linked study
Cellular health & agingLongevitySmallCNo linked study
All 7 rated effectsGrouped by health goal, with the publications behind each rating

What does vitamin C do?

Vitamin C, also called ascorbic acid, is a water-soluble vitamin that humans must obtain from their diet. It helps make collagen, the structural protein needed for connective tissue and wound healing, and contributes to antioxidant and immune functions. It also improves absorption of nonheme iron, the form found in plant foods. 1

What changes when intake is too low?

Severe deficiency causes scurvy, with fatigue, fragile connective tissue and poor wound healing. Correcting a deficiency answers a different question from adding high doses when intake is already adequate. Vitamin C’s antioxidant activity helps explain research interest in chronic disease, but a mechanism alone cannot establish a preventive benefit. 1

Key studies

The most recent publications linked to Vitamin C's ratings.

Vitamin C: A Comprehensive Review of Its Role in Health, Disease Prevention, and Therapeutic Potential2025Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials.2008Association of Oral or Intravenous Vitamin C Supplementation with Mortality: A Systematic Review and Meta-AnalysisVitamin C intake and multiple health outcomes: an umbrella review of systematic reviews and meta-analysesEffect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis
All 6 studiesEvery publication linked to Vitamin C

Why people take it

Essential Health21.8%
Immune Support20%
Energy15.4%
Bone & Joint8.2%
Cognition5.1%
Fitness4.7%

SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.

Questions people ask

Should vitamin C start only when a cold begins?

Trials starting after symptoms began have not shown a consistent benefit. 2

Is food vitamin C absorbed better than ascorbic acid?

NIH describes comparable bioavailability for food vitamin C and supplemental ascorbic acid. 1

Does vitamin C help absorb iron?

Yes, it improves absorption of nonheme iron from plant foods; high doses are a concern in hereditary iron overload. 1

Does water-soluble mean harmless?

No. High doses commonly cause gastrointestinal symptoms, and some medical conditions warrant extra caution. 1

Does a megadose improve absorption?

Fruit and vegetables supply vitamin C; progressively larger oral doses have a lower absorbed fraction. The absorption data do not establish an advantage for megadoses. 1

Sources

  1. Vitamin C: Fact Sheet for Health Professionals NIH Office of Dietary Supplements

Further reading

Illustration for Vitamin C.GuideCollagen and vitamin C: take them together or separately?Why vitamin C is needed to make collagen, what combination studies show and why adequate intake matters more than to-the-minute timing.Read the article Illustration for Vitamin C.GuideAdrenal cocktail: what orange juice, coconut water and salt actually doThe cortisol cocktail supplies sugar, electrolytes and vitamin C. What of that is supported by evidence, and when fatigue needs a different answer.Read the article Illustration for Vitamin C.GuideVitamin C in the blood: levels, supply and the limits of the testWhat a vitamin C blood level shows, why sample handling matters and when low supply should be checked by a doctor.Read the article