Vitamin C, or ascorbic acid, is water-soluble and the body cannot make it. Most mammals synthesise their own; humans, along with guinea pigs and most primates, lost that ability and have to obtain it from food.

It is abundant in ordinary food — peppers, blackcurrants, citrus, strawberries, broccoli, kale and potatoes are all meaningful sources. A single medium orange sits in the same region as the amount in this sachet.

Being water-soluble, it is not stored in any quantity. The body holds a working pool and clears the excess, which is the mechanism behind section 3 and the reason a very large single dose behaves differently from a modest daily one.

Absorption levels off

Vitamin C is taken up by a transport system that saturates. At intakes around the reference level, absorption is efficient — the great majority of what is swallowed is taken up. As the dose climbs into the hundreds of milligrams the proportion absorbed falls steadily, and at gram-level intakes a substantial share passes straight through.

What the excess does

What is absorbed beyond the body’s working pool is cleared by the kidneys. A four-figure dose therefore produces a brief peak and an expensive urine, rather than a proportionally larger effect. Unabsorbed vitamin C left in the gut is also the usual reason high doses cause digestive upset.

So 80mg is a considered choice rather than a thrifty one. It meets the reference intake in full, clears the threshold for fourteen of the fifteen claims, and does not spend sachet weight on an amount that would largely be discarded. The exception is section 4.

Fourteen of the fifteen vitamin C claims apply from 15% of the reference intake — 12mg. We carry 80mg, so all fourteen are available to us.

One is different. The claim relating to immune function during and after intense physical exercise carries its own condition: the product must provide a daily intake of 200mg. At 80mg we do not meet it, so it is not a claim we can make, and we do not make it.

We mention it because leaving it off a list without explanation is its own kind of omission. It would have been straightforward to raise the dose to 200mg and take the claim. We did not, because this is not a sports product and the honest reason for the dose is the one in section 3.

• Vitamin C contributes to the protection of cells from oxidative stress
• Vitamin C contributes to the reduction of tiredness and fatigue
• Vitamin C contributes to normal energy-yielding metabolism
• Vitamin C contributes to normal functioning of the nervous system
• Vitamin C contributes to normal psychological function
• Vitamin C contributes to the normal function of the immune system
• Vitamin C contributes to normal collagen formation for the normal function of skin
• Vitamin C contributes to normal collagen formation for the normal function of bones
• Vitamin C contributes to normal collagen formation for the normal function of cartilage
• Vitamin C contributes to normal collagen formation for the normal function of gums
• Vitamin C contributes to normal collagen formation for the normal function of teeth
• Vitamin C contributes to normal collagen formation for the normal function of blood vessels
• Vitamin C contributes to the regeneration of the reduced form of vitamin E
• Vitamin C increases iron absorption

Our pack carries the first. The rest are equally available to us at this dose.

• We do not claim vitamin C prevents or treats colds, or any other illness. No such claim has passed assessment and we would not be permitted to make one.
• We do not claim those fourteen sentences describe what this product does. They describe what the nutrient contributes to, assessed on the nutrient and not on our formulation.
• We do not make the exercise-related immune claim. It requires 200mg a day and we carry 80mg.
• We do not claim this product treats, prevents or reduces the risk of anything.

What we claim is the composition: 80mg of vitamin C, 100% of the Nutrient Reference Value.

Worth knowing

Vitamin C is well tolerated at intakes of this size. Digestive effects are associated with much larger doses, typically at gram level. If you are taking iron, note that vitamin C increases iron absorption — useful if that is intended, worth knowing if it is not. If you are managing a condition or taking medication, speak to your GP or pharmacist before adding a supplement.