The Nutrient Reference Value for vitamin C in Great Britain is 80mg a day. The best-selling supplement dose is 1000mg. Both of those are true at once, and the gap between them causes more confusion than almost anything else in this category.
Where 80mg comes from
The NRV is a labelling reference — a single figure used so that the %NRV column on a pack means the same thing on every product. It is set at a level intended to cover the requirements of most healthy adults, with a margin built in.
It is not a maximum, and it is not a target you must hit precisely. It is a yardstick. When our label says 156% NRV, that is 125mg measured against the 80mg reference — nothing more mysterious than that. There is a fuller explanation of NRVs here.
What happens at higher doses
Vitamin C is absorbed by a transport system that saturates. The practical consequences are worth knowing:
- At modest intakes, you absorb the large majority of what you take.
- As the dose rises, the proportion absorbed falls.
- Blood levels plateau. Past a point, more vitamin C raises what is in your urine rather than what is in your blood.
- Vitamin C is water-soluble and not stored, which is why a steady daily intake suits it better than occasional large doses.
None of that makes a 1000mg tablet harmful for most people. It does mean the number on the front of the pack is a poor guide to value, and that the marginal milligrams are doing less than the first ones.
The practical ceiling
The most common effect of taking a lot of vitamin C is digestive — loose stools, wind, stomach discomfort. That is the unabsorbed portion drawing water into the bowel, and it is dose-related. If a high-dose product disagrees with you, that is usually why, and taking less usually solves it.
UK guidance advises against habitually taking more than 1000mg a day from supplements.
Who has a genuine reason to take more
- Smokers. Smoking increases vitamin C turnover, and requirements are recognised as higher.
- People eating very few fruits and vegetables. Vitamin C is abundant in fresh produce and scarce almost everywhere else.
- People on plant-based diets who want the iron benefit. Vitamin C increases iron absorption, and plant iron is harder for the body to take up than iron from meat. Taking vitamin C with an iron-containing meal is a genuinely practical use of it.
- Anyone advised to by a healthcare professional. Follow that rather than this.
What vitamin C is allowed to claim
Quite a lot, and all of it specific:
- Contributes to the normal function of the immune system
- Contributes to the reduction of tiredness and fatigue
- Contributes to the protection of cells from oxidative stress
- Contributes to normal collagen formation for the normal function of skin, bones, cartilage, gums, teeth and blood vessels
- Contributes to normal energy-yielding metabolism, to normal functioning of the nervous system and to normal psychological function
- Increases iron absorption
And what it may not
No supplement may claim to prevent, treat or shorten a cold. That is a medicinal claim and it is not available to any food supplement in Great Britain, at any dose, from any source.
This matters because it is the single most common reason people buy vitamin C, and the single most commonly implied claim in the category. “Supports immunity when you need it most”, positioned next to a picture of someone sneezing, is doing work the wording is not entitled to do.
What is true is the authorised claim: vitamin C contributes to the normal function of the immune system. That is a statement about normal function, not about illness.
How this shapes what we sell
Natural Vitamin C provides 125mg a capsule — 156% NRV — from acerola cherry rather than added ascorbic acid. It is comfortably above the reference intake and well below the point where most of it is wasted.
That is a deliberate choice rather than a limitation of the formula, and it is the same reasoning set out in our buyer's guide. If you would rather have 1000mg, buy 1000mg — just buy it knowing what happens to most of it.
This is general information, not medical advice. Always read the label. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle.
0 comments