Iron (ferrous forms)

What it is

Iron is a mineral that helps make haemoglobin, the protein in red blood cells that carries oxygen. Food sources include red meat, liver, beans, lentils, fortified cereals and dark leafy greens.

Iron deficiency is common, especially in women with heavy periods, pregnancy, vegetarians and vegans, endurance athletes, blood donors and people with gut conditions or bleeding. Tiredness is the classic sign, but tiredness has many causes.

Unlike most minerals, the body has no real way to get rid of extra iron. That is why it should usually be taken because a blood test shows a need, not just in case.

How it works

Iron is absorbed in the small intestine and used to build haemoglobin and enzymes involved in energy. When you are low, absorption rises; when stores are full it falls. Vitamin C helps absorption, while tea, coffee, calcium and phytates in wholegrains reduce it.

What the evidence says

• Strong Treating iron-deficiency anaemia
  Properly diagnosed deficiency improves with iron and usually takes a few months to correct.
• Moderate Reducing fatigue in iron-deficient people
  Helps those who are low, even without anaemia, but not people with normal iron.
• Strong Pregnancy needs
  Often used under midwife or GP advice when levels are low.
• Limited Athletic performance
  Helps only when iron status is low; no performance gain if iron is normal.
• Limited Restless legs
  May help in people with low iron stores; needs testing first.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Dose depends on your blood results. Prescribed regimens may be once a day or alternate days.
• Alternate-day dosing may improve absorption and reduce gut symptoms in some research.
• Take separately from tea, coffee, dairy, antacids and calcium by a couple of hours.
• Do not self-treat for months without checking blood tests.

Forms and what to look for

• Ferrous sulphate, fumarate and gluconate: standard, cheap and effective, but can be constipating.
• Iron bisglycinate: often gentler on the gut, though it can cost more.
• Liquid iron drops: easier to take but can stain teeth.
• Avoid unnecessary slow-release products unless advised; absorption can be lower.
• Check the label for elemental iron, not compound weight.

What to expect, and when

• Haemoglobin usually starts to rise after a couple of weeks, with energy slowly improving.
• Stores generally take three months or more to rebuild.
• If you feel no better, go back for more checks rather than raising the dose.

Side effects

• Constipation
• Nausea and stomach pain
• Dark or black stools (expected)
• Diarrhoea in some
• Metallic taste

Interactions

• Reduces absorption of levothyroxine, some antibiotics (quinolones, tetracyclines) and bisphosphonates
• Antacids and proton pump inhibitors reduce iron absorption
• Calcium, zinc, tea and coffee compete with iron
• Can interact with L-dopa and mycophenolate

Who should avoid it

• Anyone with haemochromatosis or other iron-overload conditions
• Men and post-menopausal women unless a clinician advises
• People having repeated blood transfusions
• Anyone with no proven need

Risks and safety

• Iron overdose is a leading cause of fatal poisoning in young children. Keep every iron product, including prenatal vitamins, locked away; seek emergency help straight away if swallowed.
• Excess iron stored over time can damage the liver, heart and pancreas.
• Not on the WADA prohibited list, but injections need clinical oversight.
• Persistent low iron can signal blood loss that needs investigating.

Buying well: quality and testing

• Choose licensed products or those from reputable brands, with clear elemental iron per serving.
• Third-party seals like NSF or USP help.
• Avoid mega-dose gummies that look like sweets.
• Check multivitamin labels for iron if you do not need it.

Bottom line

Iron is a genuinely useful supplement when you are deficient and a poor idea when you are not. Get a blood test first, follow your clinician's plan, and treat the bottle like a medicine around children.