# Does vitamin C prevent colds?

Source: https://www.healthnews24.co.za/answers/vitamin-c-and-colds-do-supplements-help/
Publisher: Healthnews24 (South Africa's supplement answer desk)
Updated: 2026-10-27

> No. For most people, taking vitamin C regularly does not reduce how often you catch a cold, and starting it after symptoms begin does not help. Regular supplementation shortens colds slightly, by about 8% in adults and 14% in children. The exception is people under extreme physical stress, such as marathon runners, where trials found about half as many colds.

Key facts:
- Regular vitamin C shortens colds by about 8% in adults and 14% in children, but does not reduce how often you catch one in the general population (NIH summary of Cochrane).
- In marathon runners, skiers and soldiers, 250 mg to 1 g a day cut cold incidence by about 50% in trials.
- Starting vitamin C after symptoms begin did not change cold duration or severity.
- The adult upper intake level for vitamin C is 2 000 mg a day; the RDA is 90 mg (men) and 75 mg (women).

## What does the research show?

The NIH summarises placebo-controlled trials using at least 200 mg of vitamin C a day, including a Cochrane review by Douglas, Hemilä, Chalker and Treacy:

| Question | Finding | Evidence level |
|---|---|---|
| Does regular vitamin C prevent colds in the general population? | No meaningful reduction | Moderate |
| Does it shorten colds if taken regularly? | Modestly: about 8% in adults and 14% in children | Moderate |
| Does it help if started once symptoms begin? | No effect on duration or severity | Moderate |
| People under extreme exertion or cold (marathon runners, skiers, soldiers) | About 50% fewer colds at 250 mg to 1 g a day | Moderate, small number of trials |

A shorter cold by 8% means roughly half a day on a typical week-long illness. That is a small effect.

## Is it worth taking if you run Comrades or Two Oceans?

The exception in the research relates to people doing heavy, prolonged exercise or exposed to cold. If you are in a heavy build-up block, those trials used 250 mg to 1 g of vitamin C a day. However, trials did not test every kind of athlete, and many studies were small. Food, sleep, carbohydrate intake, training load and hygiene often matter more. Vitamin C is a Group B supplement in the AIS framework, meaning emerging evidence.

## How much vitamin C do you need?

| Group | NIH daily RDA |
|---|---|
| Men 19 and older | 90 mg |
| Women 19 and older | 75 mg |
| Smokers | add 35 mg |

One citrus fruit, guava, a red pepper or a cup of broccoli delivers a large share of that. The upper limit for adults is 2 000 mg a day. Above that, diarrhoea is likely, and in people prone to kidney stones high intakes could raise urinary oxalate. Stones are not generally considered a risk in healthy people.

## What can you do instead?

- **Zinc lozenges** started within 24 hours of symptoms may shorten colds by a day or two, with low-certainty evidence ([do you need a zinc supplement?](/answers/do-i-need-zinc-supplement-south-africa/)).
- **Sleep, hand washing and avoiding crowded indoor spaces** are sensible basics that cost nothing.
- **Rest and fluids** remain the foundation of care when ill.

## Should you buy a high-dose product?

Not for general cold prevention. Many multivitamins already supply 25 to 300 mg of vitamin C (for example Dis-Chem Gold Supreme Active has 60 mg, Viridian High Five 100 mg and Solgar VM-2000 300 mg per day), which covers needs. See [do multivitamins work?](/answers/do-multivitamins-work/) and [which vitamins athletes need](/answers/best-vitamins-for-athletes-south-africa/).

## When should you see a doctor?

If a cold lasts more than about ten days, if you have a high fever, chest pain, breathlessness or ear pain, or if you are pregnant, immunocompromised, or on warfarin or other medicines, speak to a doctor or pharmacist before starting a high-dose supplement. Also see [can you take too many vitamins?](/answers/can-you-take-too-many-vitamins/).

## Sources

- [NIH Office of Dietary Supplements: Vitamin C, health professional fact sheet](https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/)
- [Australian Institute of Sport Supplement Framework, Group B](https://www.ausport.gov.au/ais/nutrition/supplements/group_b)
- [NIH Office of Dietary Supplements: Zinc, health professional fact sheet](https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/)