Iron supplements: who needs them and how to take them

Iron is used to make haemoglobin, the part of red blood cells that carries oxygen. When stores run low, the body eventually cannot make enough healthy red cells, and iron deficiency anaemia follows. Tiredness, breathlessness and pale skin are the typical clues, although a blood test is the only way to confirm it.

NHS guidance gives daily iron needs of 8.7mg for men aged 19 and over, and 14.8mg for women aged 19 to 49. Women aged 50 and over need 8.7mg, or 14.8mg if they are still having periods. Good food sources named by the NHS include red meat, beans such as chickpeas and red kidney beans, nuts, dried fruit such as apricots, fortified breakfast cereals and soy bean flour. Liver is rich in iron but should be avoided in pregnancy.

The clearest group is people whose blood tests show iron deficiency anaemia. The NHS describes tablets being recommended once the anaemia is confirmed, normally after the reason for it has been looked for. Heavy periods and bleeding from the digestive tract, such as from an ulcer, are examples of causes a GP may want to rule in or out first.

Women with heavy periods are named by the NHS as being at higher risk of iron deficiency anaemia and may need supplements. Other people at risk, such as those who eat little iron-rich food or who are pregnant, are best advised by a GP, midwife or dietitian, because needs differ and the cause matters more than the tablet.

• Buying iron to treat tiredness without a blood test can mask a problem that needs investigating.

• A low blood count in an older adult or in a man warrants a search for a cause, not just replacement.

• People who have been told they have too much iron, such as in haemochromatosis, should not take iron supplements.

The NHS advice for iron deficiency treatment is to take tablets as your doctor instructs and keep taking them even when side effects occur, because stopping early leaves stores low. It suggests taking them with or soon after food to reduce the chance of side effects. It also notes that drinking orange juice after a tablet may help the body absorb the iron, while tea, coffee and milk reduce absorption.

Your repeat blood tests tell the doctor whether haemoglobin is recovering. A course often runs well beyond the point where you feel better, because the body needs time to rebuild its stores as well as its red cells. A pharmacist can advise on spacing iron from other medicines you take, as some can interact.

• Follow the dose on the label or from the prescriber, not a higher one.

• Keep a regular time each day so the tablet is not forgotten.

• Do not take it with a cup of tea or coffee.

• Store it well away from children, ideally somewhere locked.

The side effects listed by the NHS are constipation or diarrhoea, stomach pain, heartburn, nausea and darker stools. Dark stools are expected and are not in themselves a sign of bleeding, but black, tarry, sticky or foul-smelling stools, or blood in the stool, need urgent medical review.

If taking tablets with or soon after food does not settle the problem, the NHS says to ask your GP. There are different iron preparations and dosing patterns, and for people who cannot tolerate tablets or who fail to absorb them, a doctor may discuss iron given by infusion instead. Constipation caused by iron can be eased with fluids, fibre and, if needed, a short course of a laxative from the pharmacy.

The NHS states that 17mg or less a day of iron supplements is unlikely to cause harm, and that anyone needing more should take it only on GP advice. Taking more than 20mg a day may cause constipation, nausea, vomiting and stomach pain. Very high doses are dangerous, especially for children.

Many multivitamin tablets already contain iron, so combining a multivitamin with a separate iron tablet can add up. Check the label for the amount in each product before adding another.

The NHS says an iron overdose in a young child can be fatal. If a child has swallowed iron tablets, treat it as an emergency: call 999 or go to A&E, and take the packet. Do not wait for symptoms to appear, and do not try to make them vomit.

In adults, severe vomiting, blood in vomit, abdominal pain with drowsiness or collapse after taking too much iron also needs 999. Ongoing breathlessness, chest pain or fainting with known anaemia is a reason to seek same-day care.

In practice, a GP orders a full blood count and often a ferritin test, and prescribes iron tablets once deficiency is confirmed. Further tests, such as for coeliac disease or a look at the bowel, may be arranged depending on age, sex and symptoms. Treatment is then reviewed with repeat blood tests.

Supplements bought without a prescription are food supplements, not licensed medicines, and strength varies between products. A pharmacist can help you choose a product suited to your situation.