Last March, Irena Auersperger and her colleagues published a study in PloSOne showing that long distance running can deplete your iron stores, confirming previous studies. They also showed that a recovery period of ten days is not enough to fill them up again, which means that subsequent training could lead to an iron deficiency.
This is important, because more and more studies suggest that an iron deficiency could make you more tired, reduce your performances and put you in a bad mood, even if you are not anaemic. Their article confirms the idea that endurance athletes need more iron in their diet than inactive people.
The importance of iron
Iron is an essential component of haemoglobin, the substance in your blood cells that binds oxygen. It is also an essential part of the many enzymes you need to produce energy by using oxygen in your muscles (aerobic metabolism). Recent studies have shown that iron is also important for your brain.
The amount of iron you take in depends on the amount in your diet and on the presence of other food components which can increase or decrease its absorption. Vitamin C and meat increase its absorption, while calcium, bran and pectin decrease it. Vegetarians are therefore more prone to iron deficiency than meat eaters.
However, if your iron stores are low, your body will try to absorb more.
Once absorbed, it is stored by a protein called ferritin. Your blood ferritin levels are therefore a measure of your stores.
Another protein, transferrin, brings iron to young blood cells that need it to make haemoglobin. These blood cells carry receptors on their surfaces, which act like small gates to allow transferrin to deliver its iron. When there is a shortage of iron, the cells will produce more receptors, and small amounts of these receptors will appear in your blood, where they can be measured. This is considered a more reliable marker of your stores than ferritin.
When you take in less iron than your body uses, you will first deplete your stores. In a second stage, the production of red blood cells and of some tissue enzymes will decrease. Finally haemoglobin synthesis will be reduced. You therefore only develop anaemia when the deficiency is severe.
As an endurance athlete you use more iron than your sedentary counterparts, especially if you are a runner, which puts you at a higher risk of deficiency. Young women and vegetarians are the most affected, and the vast majority of the studies are therefore done on women.
For decades, scientists were not sure whether low iron stores without anaemia can affect your performances, but in the beginning of this century, Thomas Brownlie and his colleagues showed that your endurance decreases indeed and that you will tire earlier. Your training adaptation will also be reduced.
What can I do?
If you think you are at risk, ask your doctor to check your ferritin levels.
Taking supplements “just in case” is a bad idea.
Iron in multivitamin and mineral preparations typically gets badly absorbed because of the presence of other substances such as calcium.
Over the counter iron preparations usually cause gastrointestinal problems and constipation. They can even be dangerous, as too much iron is toxic. If you are genetically predisposed to a disease called haemochromatosis, an overload will damage your liver, heart and pancreas, and lead to cirrhosis and diabetes.
Taking in iron via food allows your body to match the absorption to your needs, and is therefore safe. In 1992, Roseanne Lyle and her colleagues showed that an iron-rich diet was also more effective in protecting your ferritin levels than supplements.
Even though Lyle based her iron-rich diet on animal products, it is possible to get enough iron from a vegetarian diet. However, as you absorb less from a plant based diet than from meat, you need more of it in your food. This explains why vegetarian men and premenopausal women need at least 14 and 33 mg a day respectively, which is almost twice the recommendation for meat eating men and premenopausal women (8 mg and 18 mg a day). Iron absorption is markedly increased by vitamin C. Fortunately, many vegetables are high in both, making things much easier.
Click here or here for a list of iron rich food, and here for iron-rich vegetarian recipes.
Disclaimer: this article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment. If you have any concerns or questions, you should talk to a qualified health provider.
I Auersperger, B Skof, B Leskosek et al. Exercise-induced changes in iron status and hepcidin response in female runners. PloSOne. 2013; 8(3): e58090. Published online 2013. doi: 10.1371/journal.pone.0058090. Accessed 01/07/2013.
J Beard and B Tobin. Iron status and exercise. Am J Clin Nutr. 2000; 72(2): 594s-597s.
T Brownlie, V Utermohlen, P Hinton et al. Marginal iron deficiency without anemia impairs aerobic adaptation among previously untrained women. Am J Clin Nutr. 2002; 75(4): 734-742.
T Brownlie, V Utermohlen, P Hinton et al. Tissue iron deficiency anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women. Am J Clin Nutr. 2004; 79(3): 437-443.
R Lyle, C Weaver, D Sedlock et al. Iron status in exercising women: the effect of oral iron therapy vs increased consumption of muscle foods. Am J Clin Nutr. 1992; 56(6): 1049-1055.