Vitamin C: how much a child needs, and where it comes from

An Australian child aged 4 to 8 needs 35 mg of vitamin C a day. From 9 to 13 it is 40 mg, and from 14 to 18 it is 40 mg for girls and 45 mg for boys. Those are the Nutrient Reference Values used in Australia and New Zealand, and they are lower than most parents expect.

Here is what the vitamin does, how much is in ordinary food, and why the source on a label is worth reading.

What vitamin C is doing

Vitamin C is one of the few nutrients where Australian food law has already decided what may be said about it. Under Schedule 4 of the Food Standards Code these are pre-approved statements, which means they have been assessed and permitted rather than argued for by a brand:

• Vitamin C contributes to the normal immune system function.
• Vitamin C contributes to normal growth and development in children.
• Vitamin C contributes to normal psychological function.
• Vitamin C is necessary for normal neurological function.

That last pair is the part most people have not heard. Vitamin C is not only an immune nutrient. The brain concentrates it heavily: cerebrospinal fluid runs several times higher than blood, and inside neurons the concentration is higher again. Part of the reason is that vitamin C is the cofactor for the enzyme that converts dopamine into noradrenaline. (Harrison and May, Free Radical Biology and Medicine, 2009, PMID 19162177.)

There is a second, quieter job. Vitamin C substantially improves the absorption of iron from plant foods, which matters in any household where meat is not a daily event.

Where children fall short

For most children eating a normal mixed diet, vitamin C is not a problem. One orange covers the day.

The exception is children who eat a short list of foods, and that is a large group. An Australian tertiary children's hospital reviewed three years of vitamin C testing in patients from birth to 18. Of the children tested, 31 per cent had levels below the deficiency threshold, and 65 per cent of those had restricted eating. (van Heerden et al., Journal of Paediatric and Child Health, 2024, PMID 39031615.)

Those were children a doctor had a reason to test, so it is not the community rate. But the pattern is real: if fruit and vegetables are a battle in your house, vitamin C is the nutrient most likely to be quietly low.

Whole food or synthetic

Most vitamin C in supplements is ascorbic acid made by fermentation from glucose. It is chemically identical to the ascorbic acid in an orange, and at the level of the molecule your body cannot tell the difference.

The difference is what comes with it.

Acerola cherry, sometimes called the Barbados cherry, is one of the richest natural sources of vitamin C on earth, containing many times the vitamin C of an orange by weight. When vitamin C is delivered as acerola, it arrives inside the fruit's own matrix, alongside the polyphenols and carotenoids that grew with it, rather than as an isolated compound.

It is also worth knowing that it takes only a small amount of acerola powder to reach a meaningful figure, which is why you will see it in the low tens of milligrams rather than as a bulk ingredient.

How to read the number on a label

Three checks, in order.

First, the amount in milligrams, not just a percentage. A percentage is only useful if you know whose reference figure it is.

Second, whose reference figure it is. Most percentages on labels are calculated against adult intakes unless the label says otherwise, so a claim of 25 per cent of your daily needs on a children's product may or may not be 25 per cent for your child.

Third, the source. Vitamin C on its own tells you the nutrient. Vitamin C from acerola cherry tells you the nutrient and where it came from, and a company willing to name the source is usually willing to name other things too.

More is not better

Vitamin C is water soluble, so what the body cannot use is largely excreted. Very large amounts in children have been tried in research and have not produced benefits worth repeating, and high intakes can cause digestive upset.

The useful target is the reference intake, met reliably every day, rather than a large number met occasionally.

What to take from it

A child needs 35 to 45 mg of vitamin C a day depending on age. It supports immune function, growth and development, psychological function and neurological function, in wording Australian food law has already approved. Children who eat a narrow range of foods are the ones most likely to run low.

On a label, look for the milligrams, the age the percentage refers to, and the source.