What is iron, and what does it do in the body?

Iron is a mineral the body cannot make and has to take in from food every day. The total amount in an adult body is small, but it sits where it matters. About two-thirds is in haemoglobin, the protein inside red blood cells; some is in myoglobin in muscle, and the rest is held in the liver, spleen and bone marrow.

What does iron do in the body?

Four nutrient function statements for iron are recognised in the annex to Thai Ministry of Public Health Notification No. 447 (B.E. 2566):

• Iron contributes to normal formation of red blood cells and haemoglobin
• Iron contributes to normal oxygen transport in the body
• Iron contributes to normal energy-yielding metabolism
• Iron contributes to the normal function of the immune system

These describe the nutrient itself, not an effect of any product.

Why does haemoglobin need iron?

Haemoglobin picks up oxygen in the lungs and carries it to tissue throughout the body. Each haemoglobin molecule carries four haem groups, with an iron atom at the centre of each. That is why the first two statements above are really one idea.

How is iron connected to energy and immunity?

The other two get less attention. Iron contributes to normal energy-yielding metabolism and to the normal function of the immune system.

How much iron does the body need each day?

Recommended intakes set by the US National Academies' Food and Nutrition Board, as published by the NIH Office of Dietary Supplements, are 8 mg a day for adult men and 18 mg a day for women aged 19 to 50. From age 51 the figure for women is 8 mg, and it rises during pregnancy. The tolerable upper intake level for adults is 45 mg a day from all sources combined.

These are population reference figures, not personal advice.

Where does dietary iron come from?

Dietary iron comes in two forms. Haem iron, from animal foods such as pork blood, liver and red meat, is absorbed at a fairly steady rate. Non-haem iron, from plants such as dark leafy greens, dried beans, tofu and sesame, is absorbed to a degree that depends more on what else is in the meal: oxalate in spinach and phytate in beans and grains limit it, and soaking or fermenting reduces phytate.

The same notification separately recognises that vitamin C increases iron absorption, which is why putting a vitamin C-rich vegetable or fruit in the same meal as plant-source iron is a sensible habit.

How do you read the label?

Labels usually give the weight of the compound first, with the amount of elemental iron in brackets, for example iron amino acid chelate 36.50 mg (provides iron 7.30 mg). The bracketed figure is the one to compare between products.

What should you watch out for?

The body has no easy route for clearing excess iron, so more is not better. Treat the amount on the label as a ceiling.

If you are pregnant, breastfeeding or taking prescription medication, speak to a doctor or pharmacist before supplementing.

Dietary supplements are not intended to prevent, treat or cure any disease.