Vitamin C: dietary needs, supplements and the limits of health claims

Vitamin C is an essential nutrient found mainly in fruit and vegetables. It supports collagen formation and helps absorb non-haem iron. A tablet is not a universal health guarantee: the value of a supplement depends on diet, nutritional status and medical context.

EFSA reference values describe healthy populations; they are not an individual dosing plan. Food sources include citrus fruit, blackcurrants, peppers and parsley. Cooking and storage can reduce vitamin C, but do not make fruit and vegetables irrelevant.

Food provides vitamin C within a broader diet. A supplement provides an isolated, concentrated dose. Food and supplements are not automatically interchangeable.

Severe deficiency can cause scurvy, with bleeding gums, joint pain or poor wound healing. Risk is higher with a very restricted diet, smoking, malabsorption or some chronic diseases. Symptoms alone cannot diagnose deficiency.

For most people, regular vitamin C does not lower the chance of catching a cold, but Cochrane trials show a modest reduction in cold duration; starting it after symptoms begin has no consistent effect.

Some studies suggest a different result in people exposed to extreme physical stress or with marginal vitamin C status. This does not justify a general prevention promise.

High intakes can cause diarrhoea, nausea and abdominal cramps. Vitamin C may alter urinary oxalate and uric-acid excretion, so extra caution is appropriate with kidney disease, previous stones or hyperoxaluria.

In haemochromatosis, vitamin C can increase iron absorption and worsen iron overload. High-dose supplements are not harmless in that setting.

Vitamin C can alter iron absorption and may interact with some medicines or measuring devices; the context should be checked with a healthcare professional. During pregnancy, avoid multiplying vitamin and mineral sources without an established need.

1. 01EFSA, 2013 — https://www.efsa.europa.eu/en/efsajournal/pub/3418
2. 02ANSES, 2020 — https://www.anses.fr/fr/content/vitamine-c
3. 03NIH Office of Dietary Supplements, 2024 — https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
4. 04Cochrane, 2013 — https://cochrane.org/evidence/CD000980_vitamin-c-preventing-and-treating-common-cold
5. 05NIH Office of Dietary Supplements, 2024 — https://ods.od.nih.gov/factsheets/ImmuneFunction-HealthProfessional/