Iron

The metal at the centre of haemoglobin, which is what carries oxygen around your body. Your body has no route for getting rid of excess, so it regulates iron at the point of absorption instead — which makes both shortage and overload possible.

Carries oxygen — it sits at the centre of haemoglobin in blood and myoglobin in muscle. Also needed for energy production and immune function.

• Red meat and liver
• Shellfish
• Legumes and lentils
• Tofu
• Fortified cereals
• Dark leafy greens
• Pumpkin seeds

Plant iron is absorbed poorly — vitamin C alongside it improves that substantially, while tea, coffee and calcium taken with the meal reduce it.

8 mg (men) · 18 mg (menstruating women) · 27 mg in pregnancy for most adults. The upper limit, past which harm becomes likely, is 45 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: Iron deficiency anaemia. 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: Menstruating women, pregnancy, vegetarians and vegans, endurance athletes, and anyone with gut bleeding — which is why unexplained iron deficiency in men and older women is investigated.

Blood loss is the commonest cause in adults: heavy periods, and in anyone else, bleeding somewhere in the gut until proven otherwise. Also increased demand in pregnancy and growth, low intake on a diet without meat, coeliac disease, and reduced absorption after stomach surgery or on long-term acid suppression.

The most common nutritional deficiency in the world. Fatigue, breathlessness, pallor, cold hands, brittle nails, and sometimes a craving for ice or dirt. Affects concentration long before anaemia appears on a blood test.

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

Ferritin reflects stores and is usually the most useful single test, but it rises with any inflammation and can look reassuring while stores are empty. A full blood count, transferrin saturation and CRP together give a clearer picture than ferritin alone.

Haem iron from meat, fish and poultry is absorbed several times more readily than the non-haem iron in beans, lentils, tofu and dark leafy greens. Vitamin C alongside a plant source improves absorption noticeably; tea and coffee with a meal reduce it, so move them to between meals.

Ferrous sulphate, fumarate and gluconate are all commonly used, and constipation and nausea are common with all of them. Alternate-day dosing is now often better tolerated and absorbed than daily. Iron supplements are a leading cause of poisoning in small children — keep them out of reach.

Iron supplements are a leading cause of fatal poisoning in young children — keep them locked away. In adults, excess causes constipation and nausea; in haemochromatosis it accumulates and damages the liver, heart and pancreas. Do not supplement without knowing your levels.

Interactions: Reduces absorption of levothyroxine and several antibiotics — separate by four hours.