Vitamin C

Does vitamin C prevent or shorten colds?

Updated 3 Nov 2026

Short answer

In most people, taking vitamin C every day does not prevent colds, but it makes them a little shorter: by 8% in adults and 14% in children.[1] In marathon runners, skiers and soldiers on exercises in the subarctic, it halved the risk of a cold.[1] Started only after a cold began, it had no consistent effect.[1]

What the Cochrane review found

A 2013 Cochrane review pooled placebo-controlled trials that gave at least 200 mg of vitamin C a day.[1] It left out trials with less than 200 mg a day and trials without a placebo group.[1] Most of the trials were randomized and double-blind, and leaving out the others did not change the conclusions.[1] It asked three questions: does daily vitamin C stop colds, does it make them shorter, and does it help when taken only after a cold starts.[1]

The results for daily vitamin C were:[1]

  • Catching a cold, general population. In trials with 10,708 people, the risk ratio was 0.97, almost no difference. A risk ratio of 1 means the same risk as placebo.[1]
  • Catching a cold, heavy physical stress. In 5 trials with 598 marathon runners, skiers and soldiers on exercises in the subarctic, the risk ratio was 0.48. About half as many caught a cold.[1]
  • Length of a cold. In 31 comparisons with 9,745 colds, colds were 8% shorter in adults and 14% shorter in children.[1]
  • Higher doses in children. With 1 to 2 g a day, colds in children were 18% shorter.[1]
  • Severity. Colds were also milder.[1]

An 8% shorter cold means that a cold of 7 days lasts about half a day less.[1]

Taking it only when a cold starts

Seven comparisons, with 3,249 colds, tested vitamin C started after the first symptoms. They found no consistent effect on how long or how bad the colds were.[1] The review authors called for more trials of this kind.[1]

Severe symptoms

A 2023 meta-analysis by the same authors pooled 10 trials of at least 1 g a day in healthy people.[2] Vitamin C made colds 15% less severe.[2] In the 5 comparisons that measured both, it shortened severe symptoms but had no clear effect on how long mild symptoms lasted.[2]

Why it may work

The steps that a 2017 review describes:[3]

  1. Neutrophils, white blood cells that kill germs, collect vitamin C.[3]
  2. Vitamin C can help them move toward germs, take them in and kill them.[3]
  3. An infection uses up vitamin C, so its level in the body falls.[3]

High doses of vitamin C may also act as an antihistamine.[4]

Who should be careful

Doses of 1 to 2 g a day are below the US upper limit of 2,000 mg for adults, but high doses can cause diarrhea, nausea and stomach cramps.[4] Children have lower limits: 400 mg a day at 1 to 3 years and 650 mg at 4 to 8 years.[4] People with kidney stones or hemochromatosis should ask a doctor or pharmacist first.[4]

Sources (4)

  1. Vitamin C for preventing and treating the common cold. Hemilä H, Chalker E Cochrane Database Syst Rev, 2013. PMID 23440782
  2. Vitamin C reduces the severity of common colds: a meta-analysis. Hemilä H, Chalker E BMC Public Health, 2023. PMID 38082300
  3. Vitamin C and Immune Function. Carr AC, Maggini S Nutrients, 2017. PMID 29099763
  4. Vitamin C: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov

More about vitamin c

What is vitamin C?How much vitamin C do you need a day?What is vitamin C used for?What are the signs of vitamin C deficiency?Is vitamin C safe?Does vitamin C lower blood pressure?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.