Iron is an essential mineral which is vital for health. It forms part of the red blood pigment, haemoglobin, which transports oxygen around the body for use by all cells, including brain cells. This function of iron is so important that of your body’s total of 2g – 3g of iron, two-thirds are tied up in your circulation.
Iron also forms part of the red muscle pigment, myoglobin, which regulates oxygen storage in muscle fibres, and forms a critical part of some metabolic enzymes such as the cytochromes.
The EU has authorised several health claims that iron contributes to:
- normal cognitive function
- normal energy-yielding metabolism
- normal formation of red blood cells and haemoglobin
- normal oxygen transport in the body
- the normal function of the immune system
- the reduction of tiredness and fatigue
- the process of cell division
- normal cognitive development of children.
What are the best dietary sources of iron?
Many foods are also fortified to help prevent iron deficiency. Within some countries, such as the UK, white and brown flour is fortified by law to a level of at least 16.5 mg iron/kg flour. Some manufacturers also fortify breakfast cereals with iron on a voluntary basis (typically 70 to 120 mg/kg) to replace some of that lost during processing.
Infant formulas and follow-on milks are also fortified by EU law, and overall, fortification accounts for around 10% of the iron obtained by adults and over 20% of the iron consumed by preschool children.
Haem and non-haem iron
The iron in food is present in two main forms:
- Haem (heme) iron – the protein-bound form obtained from the pigments in animal-based foods.
- Non-haem iron – from plant sources, fortified bread and cereals.
All forms of iron are absorbed almost exclusively with the first part of the small intestine – the duodenum.
Haem iron is absorbed two or three times more efficiently than non-haem iron, as it is taken up via a specific haem receptor. So, although haem iron only accounts for 5% to 10% of dietary iron in most western countries, it contributes between 20% and 30% of the iron absorbed into the body.
Most dietary iron is obtained from non-haem sources, however, with around half of the iron in a typical western diet coming from cereal products, and around 16% from vegetables.
Non-haem iron exists in two oxidation states: ferrous iron (Fe2+) and ferric iron (Fe3+) each of which has its own separate absorption mechanism.
Ferric iron – the form in which most plant derived iron is obtained – is less well absorbed due to its poor solubility in the alkaline juices of the duodenum. This means that only around 1% to 10% of dietary non-haem iron is extracted during digestion. The absorption of ferric iron can be improved by eating plant foods with a vitamin C source, such as fresh orange juice. The vitamin C (ascorbic acid) converts ferric iron to the more soluble ferrous iron within the stomach. Over boiling vegetables, however, decreases their iron availability by up to 20 per cent – partly because it denatures the vitamin C that is naturally present.
Substances known as phytates, which are found in nuts, seeds and cereal products, plus some plant polyphenols (especially tanins) bind to iron and block its absorption to decrease its availability even further, although this is counteracted by the presence of vitamin C.
People who mainly eat a plant-based diet are therefore at increased risk of iron deficiency as their intake depends on absorbing non-haem iron.
Ferritin – an iron storage protein found in both animals and plants – may also provide a source of dietary iron although this is somewhat controversial. Researchers are not yet certain how ferritin iron is absorbed, and it may be digested down to release ferrous iron, but this remains to be determined. There may be a separate uptake receptor for ferritin, or it may pass through the intestines taking its iron with it.
For breast-fed infants, the main source of iron is lactoferrin, a protein that binds two ferric irons. If the mother is iron deficient, however, this will affect her ability to produce lactoferrin.
Worldwide, iron deficiency is the most common nutritional disease, yet most cases go unrecognized. Women are more at risk of iron deficiency than men, because of blood losses during menstruation. This can result in a low-grade iron deficiency that is enough to impair immunity, without causing frank iron-deficiency anaemia and is best diagnosed by measuring circulating blood levels of an iron-storage protein called ferritin. Possible signs of having a low iron store is experiencing the annoying condition known as restless legs syndrome, and an increased susceptibility to Candida yeast infections.
Iron deficiency anaemia
A pronounced iron deficiency leads to the production of red blood cells that are smaller and paler than normal due to a lack of the red blood pigment, haemoglobin. This results in iron-deficiency anaemia with paleness, rapid pulse, tiredness, exhaustion, dizziness, headache, shortness of breath and even angina if the anaemia is severe.
Lack of iron reduces oxygen supply to brain cells, making it difficult to think straight and reducing work performance. During childhood, iron deficiency anaemia is particularly associated with behavioural problems, poor concentration and learning difficulties.
As iron is needed for white blood cells to produce the chemicals they need to fight infections, deficiency is also associated with impaired immunity. Lack of iron reduces fertility and makes it difficulty to keep warm – a particular problem for the elderly.
Other symptoms that can indicate iron deficiency include generalized skin itching, having concave brittle nails, hair loss, sore tongue, cracking at the corners of the mouth, reduced appetite and difficulty in swallowing. A few people with iron deficiency may develop cravings for non-food items such as eating coal, soil, paper or even rubber bands – a condition known as pica.
Iron intakes have fallen over the last three decades, partly due to decreased meat consumption. As a result, iron deficiency anaemia is increasingly common. Vulnerable groups include:
- Infants who are exclusively breast-fed
- Menstruating women
- Pregnant women
If you think you could have iron-deficiency anaemia, it’s important to seek medical advice before taking iron supplements unless you know for certain that a poor diet is to blame.
Other possible causes such as hidden blood loss, heavy periods or conditions affecting the formation of red blood cells in the bone marrow may need investigation. Blood tests are most useful when performed before starting iron supplements which may mask the iron deficiency and delay diagnosis of the underlying cause.
Excess iron is toxic
Perhaps oddly, there is no specific mechanism for excreting excess iron. This may seem odd, but the regulation of iron intake normally occurs at the level of the duodenum to prevent too much being absorbed into the circulation. This is achieved by storing the iron extracted from the diet within the lining cells of the duodenum.
- If the body’s iron stores are full, the newly absorbed iron stays in the lining cells and is shed within three or four days into the intestinal tract and excreted.
- If the body’s iron stores are not full, this triggers the production of an iron transporter protein which allows the iron to pass across from the lining cell to enter the circulation.
The regulation of iron absorption into the body is highly complex and still under investigation. When it goes wrong, then excess iron can accumulate in the liver and lead to generalised iron overload (excess total body iron >5g in adults) or severe iron overload (excess total body iron >10g). Iron is especially toxic to young children in whom the mechanisms that regulate iron uptake are not fully mature. Keep iron supplements out of reach of infants as fatalities have occurred.
Iron is highly reactive and rapidly oxidised which is seen most obviously when iron items rust.
In the body, a similar process occurs when excess iron interacts with body tissues to cause oxidative tissue damage. This effect is normally minimised as most body iron is bound to carrier molecules with antioxidant properties, and because iron absorption is carefully regulated in the duodenum.
Haemochromatosis is a condition in which the absorption of non-haem iron continues without regulation, even when body stores are replete. It occurs when someone inherits two copies of a ‘faulty’ gene which, in 90% of cases, is the HFE hereditary haemochromatosis gene.
Among Caucasians, haemochromatosis affects around 1 in 200 people. Another 1 in 100 carry a different gene mutation which also increases iron accumulation, but to a lesser extent. In addition, around 1 in 10 people have one copy of the ‘faulty’ genes involved which can mildly increase iron stores, although significant iron loading is rare.
Excess iron accumulates within the internal organs to produce a variety of symptoms including malaise, fatigue, joint pains, and bronzing or greying of the skin. It is sometimes diagnosed when routine blood tests show elevated liver enzymes, but by the time symptoms trigger investigations, males are not usually diagnosed after their forties and women several decades later, after menstruation ceases at menopause.
If undiagnosed and untreated, the toxic effects of iron can lead to liver cirrhosis, diabetes due to pancreatic damage, and heart failure.
Treatments involve having regular blood extractions (similar to when donating blood), or taking desferrioxamine, an iron-chelating compound. Nutritional approaches include:
- Limiting intakes of iron rich foods, especially red meat, and vitamin C which enhances non-haem iron absorption
- Avoiding or limiting alcohol (which is also a liver toxin)
- Increasing intakes of substances that bind iron to limit its absorption, such as tea (high in tannins), calcium, and foods that contain oxalic acid (eg rhubarb, amaranth, spinach, chard, beets, cocoa, nuts, berries, and beans) and phytic acids (grains, nuts and legumes). These must be eaten at the same time as the iron-containing foods to limit iron absorption.
Iron and coronary heart disease
Excess iron may oxidise ‘bad’ LDL-cholesterol to promote hardening and furring up of the arteries. Early studies found that Finnish males with raised blood levels of ferritin (suggesting high iron stores) were more than twice as likely to experience a heart attack as those with lower levels, after taking other factors into account such as age, exercise level, smoking, blood pressure, glucose and lipid levels. At the same time, Finnish males who regularly donated blood (and therefore lost approximately 250mg haem iron per 500mg donated) were found to have an 88% reduced risk of a heart attack compared with non-blood donors. But people with haemochromatosis do not seem to have an increased risk of heart attack (though they are at risk of heart failure) and these findings remain unexplained. Some large analyses of all the data have found no significant differences in risk between those with the highest iron status and those with the lowest iron status, while others have found that haem iron intake increases the risk.
Iron and pregnancy
Iron requirements are thought to increase during pregnancy as red blood cell and haemoglobin counts go up by around 30%. However, much of this extra iron requirement is met through the absence of normal losses associated with menstrual bleeding. Pregnancy is also associated with a significantly increased ability to absorb from the diet – in fact, iron absorption becomes up to 9-fold more efficient during pregnancy than before (or after).
At one time, iron was routinely prescribed during pregnancy because haemoglobin levels naturally tend to fall. This does not necessarily mean there is an iron deficiency however, but may result from a general dilution of blood. Although iron is important during pregnancy, and blood counts are monitored, iron supplements are no longer routinely recommended as excess intakes have been associated with an increased risk of developing pre-eclampsia.
How much iron do you need?
In normal healthy adults, between 0.5mg and 2 mg of iron is lost every day due to the constant exfoliation of iron-containing cells that line the gastrointestinal and urinary tracts, as well as the iron present in shed skin cells and hair. The same amount of iron is therefore needed from dietary sources to maintain body iron levels. As absorption from food is not always efficient – especially of ferric iron – higher intakes are needed to ensure sufficient uptake.
The EU RDA for iron is 14mg for adults. The upper safe level for long-term use from supplements (in addition to that in food) is suggested as 17mg per day.
Most men and post-menopausal women do not need to take iron-containing supplements unless they do not eat red meat.
If you decide to take an iron supplement, select one supplying iron in the ferrous (not the ferric) form. Ferrous fumarate and ferrous gluconate are usually better tolerated than ferrous sulphate which can cause nausea and constipation.
Iron-rich spa water is available as a liquid iron tonic, as are iron-rich solutions/tablets obtained from plant sources (herbal tonics) which are also well tolerated and may act more quickly.
Vitamin C increases the absorption of non-haem iron when taken at the same time, so it is a good idea to wash down supplements with fresh fruit juice.
Iron is best taken on an empty stomach and washed down with orange juice to boost absorption. Don’t wash it down with tea or coffee, as their tannins can reduce iron absorption by up to 39% if drunk within an hour of eating.
Avoid taking too much iron as this can cause constipation or indigestion and excess is toxic (especially for children).
Keep iron supplements well away from small children – eating just a few has been known to be fatal.
Taking iron supplements alone can decrease absorption of zinc and other essential minerals (such as manganese, chromium and selenium) so it is usually advisable to only take iron in combination with these, e.g. in an A to Z-style vitamin and mineral supplement (unless prescribed individually by a doctor).