Vitamin C at a Glance
Vitamin C: the whole thing in five minutes, for when you want the numbers and nothing else.
A water-soluble vitamin required for collagen synthesis and immune cell function.
Key takeaways
- UK adult reference intake: 40mg a day
- Effect on catching a cold: no reliable effect in the general population
- Most useful single change: Get it from food, which is easy and cheap at this intake.
- Commonest mistake: High-dose supplements expecting to prevent colds.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
The numbers, in one place
| Measure | Figure |
|---|---|
| UK adult reference intake | 40mg a day |
| Effect on catching a cold | no reliable effect in the general population |
| Effect on cold duration | at best a small reduction |
| Main food sources | citrus, peppers, broccoli, strawberries, potatoes |
| High doses | commonly cause diarrhoea and can raise kidney stone risk |
In one paragraph
It is the most heavily marketed cold remedy and among the least supported, with trials suggesting at most a small reduction in duration.
Worth doing
- Get it from food, which is easy and cheap at this intake
- Include a vitamin C source with plant sources of iron to aid absorption
- Store and cook vegetables briefly; it degrades with heat and time
Worth avoiding
- High-dose supplements expecting to prevent colds
- Very high doses if you have a history of kidney stones
- Assuming a supplement replaces a varied diet
Where to go next
- Starting Out With Vitamin C
- Vitamin C: The Questions People Actually Ask
- Vitamin C — the reference entry
- Zinc: What the Evidence Actually Says
- Gut Health and Immunity: What the Evidence Actually Says
When to speak to a doctor
See a GP for bleeding gums, easy bruising, poor wound healing or unexplained fatigue, which can rarely indicate deficiency. Speak to your GP before taking high doses if you have kidney disease or a history of kidney stones.
Where this comes from
- NHS — Vitamin C
- British Nutrition Foundation — vitamins
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.
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