Vitamin C

Water-soluble, not stored, and needed daily. Its central job is building collagen, which is the connective tissue holding skin, blood vessels, gums and bone together — and the reason a long shortage produces the specific picture of scurvy.

Required to make collagen, which is why deficiency shows in skin, gums and wound healing. Also an antioxidant, helps recycle vitamin E, and greatly increases absorption of plant iron.

• Peppers
• Citrus fruit
• Strawberries and kiwi
• Broccoli and Brussels sprouts
• Blackcurrants
• Potatoes

Absorption falls sharply above about 200 mg at a time — splitting doses is better than one large one.

90 mg (men) · 75 mg (women) · +35 mg for smokers for most adults. The upper limit, past which harm becomes likely, is 2,000 mg.

Reference intakes are population figures. Pregnancy, illness, age and medication all move an individual’s needs, which is one of several reasons this page is information rather than advice.

A sustained shortage has a name here: Scurvy. That is worth pausing on — nutrients whose deficiency earned a name are the ones where the consequences were severe enough, historically, to be described as a disease.

Most at risk: Smokers need more. Also people eating very restricted diets, and heavy drinkers.

Genuinely low intake over weeks to months: very restricted diets, alcohol dependence, isolation, and eating disorders. Smoking increases requirement. Outright scurvy is rare but still occurs.

Bleeding gums, bruising, poor wound healing, corkscrew hairs, joint pain and profound fatigue. The disease that killed more sailors than combat, and the reason the vitamin was found at all.

Every sign here has other, often likelier, explanations. A list of symptoms is a reason to look into something, never a diagnosis.

Plasma vitamin C can be measured but is rarely needed — the diagnosis is usually made on diet history and the appearance of the gums and skin, and confirmed by how quickly it responds to treatment.

Peppers, citrus, kiwi, strawberries, broccoli and tomatoes. It degrades with heat, light and time, so raw or lightly cooked and reasonably fresh keeps more of it.

Absorption falls sharply above roughly 200 mg at once, so very large doses mostly end up in urine. High doses can cause diarrhoea and, in susceptible people, contribute to kidney stones.

Excess is excreted, but large doses cause diarrhoea and stomach cramps, and raise the risk of kidney stones in susceptible people.

Interactions: Greatly increases non-haem iron absorption, which matters both to vegetarians and to people with haemochromatosis, who should be careful.