Nutrition: Why you need iron

By: Dr Chris Fenn

You won't get very far without enough iron in your body. But why do you need it, and just how much do you need?

Iron is the most abundant metal on the planet but the amount in our bodies is small - equivalent to that found in a large nail. Iron is bound up with protein molecules. If this is globin, the complex is haemoglobin, which is then packaged into red blood cells. Its function is to shuttle oxygen from your lungs to your cycling muscles and take the waste carbon dioxide back to your lungs on the return trip.

The ability of haemoglobin to pick up and release gasses depends on the iron content. If you don't have enough, your oxygen-carrying capacity and thus your exercise performance is affected. You feel tired, lethargic and suffer more headaches than usual.

Other protein/iron complexes are enzymes such as peroxidase and the cyctochrome enzymes. These are a vital part of the energy production systems, deep within your muscle fibres. Once again, a lack of iron will have a direct affect on your energy levels.

Replenish your stock

To avoid being deficient in iron, you simply need to replace the amount you lose each day. This is a mere 1mg in men, which is mostly via the normal exfoliation of skin cells and sweat. In women, the loss of menstrual blood represents an extra loss of about 0.5mg per day.

These normal losses of 1-2mg per day are small in comparison with an average diet, which supplies 10- 15mg per day, and yet iron deficiency is common among people who exercise regularly. Early signs are a pale skin (that's before you get on your bike and start working hard!); a lack of colour and pinkness indicates that there's not enough healthy, iron-rich blood. Look inside your eyelids; they should be a bright red colour.

Other deficiency symptoms include a sore tongue or cracks at the side of your mouth. Vertical ridges along your fingernails can also be as a result of iron deficiency.

Routine blood tests will measure haemoglobin and haematocrit levels, but these are only reduced in the final and more severe stages of iron deficiency. You can be mildly iron deficient, even if these show as normal.

If you do suspect a deficiency, ask your doctor to test for serum ferritin or total iron binding capacity, which are more sensitive indicators of a deficiency.

Iron's ions

There are plenty of foods that contain iron, but the actual amount that gets into your body can be very small. This is because the form of iron (Fe) that we need is 'ionic' which means it carries a 2+ or 3+ charge.

Within haemoglobin, the iron can flip backwards and forwards between the two positive states - this is how it can pick up and release oxygen molecules. However, during digestion, it also means that the iron ions like to stick to other molecules, such as the wholemeal bread you have eaten. The fibre it contains carries a negative charge and attracts the positively charged iron ions (with the more positively charged Fe3+ state binding even more tightly compared with Fe2+). Within the gut, the iron clings to the bran in the bread and is then passed out in faeces.

The iron in animal foods is in a different form. It isn't positively charged and is held within a protective protein coat. The entire iron-protein complex is absorbed intact, which is why the iron from meat, eggs and fish is more readily absorbed compared to that from wholemeal bread or bran flakes.

However, if you don't eat meat, the good news is that vitamin C is a powerful promoter of iron absorption. It helps convert any Fe3+ in the body to Fe2+. This form carries a less positive charge and is absorbed up to four times more easily compared to the Fe3+ form. So stock up on eating foods rich in vitamin C - oranges, kiwi fruits, broccoli, kale, tomatoes, peppers and new potatoes (which also contain some iron), or drink orange juice with your iron-enriched breakfast cereal.

However, the positive effects on iron absorption will be reduced if you also drink well-brewed black tea. The tannins strongly bind any iron present, making it less available for absorption.

Iron supplements are not always the answer. Avoid those containing iron sulphate, which is difficult to absorb. Read the label and choose iron fumarate, citrate or amino-acid chelated iron. However, it's better to obtain minerals in their natural form.

If you feel you need an iron supplement, take the pills for a couple of months and monitor how you feel. Excess iron is not easily excreted and it is possible to get too much of a good thing.