Iron is an essential mineral that is required to support aerobic performance and endurance capacity in athletes. Iron is also essential for the regulation and growth of cells, for thyroid hormone metabolism, neural function and for the immune system. Iron in the body can be divided in 3 categories:
Storage iron
Iron is stored as ferritin in cells of the immune system that reside in the liver, spleen and brain. Ferritin is an intracellular protein that stores and releases iron as required and acts as a buffer between iron deficiency and overload. Small amounts of ferritin circulate in the blood; the amount of ferritin in your blood (serum ferritin) is directly related to the amount of iron stored in the body. Normal serum ferritin levels are between 30 – 400 ug/L. As iron levels in the body increase so do serum ferritin levels, and serum ferritin is generally used as the most reliable marker for a person’s iron status.
Transport iron
Iron being transported around the body in the blood comes in various forms – free iron dissolved in plasma and iron bound to transferrins. Free iron is not a reliable marker for iron status as it has a diurnal pattern – being higher in the morning and lower in the evening. Normal serum iron levels are between 11 – 28umol/L.
Transferrins are an iron-binding protein produced in the liver that carry iron from the storage sites to the bone marrow for erythropoiesis. Transferrins also show a wide diurnal pattern and are not considered a good marker for iron status in athletes. The amount of iron that can bind to transferrins along with the capacity of the transferrins to accept iron (termed total iron binding capacity or TIBC) is referred to as transferrin saturation and expressed as a ratio. A transfferin saturation ratio of between 20-55% is normal. Anything less than about 16% is considered to be a cutoff point where red blood production will be compromised; anything greater than 60% is considered a sign of hemochromatosis. Normal TIBC levels are 41 – 77 umol/L.
The uptake of iron delivered to the cells by transferrins is controlled by cell surface receptors called transferrin receptors. Breakdown products of these transferrin receptors can be measured in the blood (serum transferrin receptors) and can be used as a marker of early functional iron deficiency. As serum ferrintin goes down serum transferrin receptors increases. Normal serum transferrin receptors values should be less than 8.5mg/L.
Red cell iron
Iron is used in the formation of haemoglobin – part of the red blood cell that is used to carry oxygen from the lungs to working muscles during exercise. It is used in the formation of myoglobin – responsible for facilitating the transport of oxygen into the mitochondria; and it is used as a component in the electron transport chain for the production of ATP. As iron levels in the body decrease the number of red blood cells and haemoglobin will decrease. The body only contains a very small amount of total iron – between 3mg and 4mg as it is a toxic metal. There is about 60-70% of this iron bound up in haemoglobin and 10% bound up in myoglobin.
Faulty iron levels
Two faulty iron states can occur. Iron excess in a condition such as hemochromatosis – a genetic condition where you absorb too much iron from your food leading to organ damage, and iron deficiency. Even a small iron deficiency can reduce oxygen binding capacity and aerobic performance, thus affecting athletic performance. Athletes can have a simple blood test to assess their iron status. Most research seems to use serum ferritin as the marker to distinguish iron status. However other markers such as haemoglobin, serum iron, transferrin saturation, serum transferrin receptors and TIBC should be considered.
Three groups of athletes are susceptible to iron deficiency – females, distance runners or endurance athletes and vegetarians. Children are also susceptible to iron deficiency especially those engaged in endurance events due to the requirements of iron for growth and exercise. Although low iron stores can affect around 20-30% of female athletes the prevalence of iron deficiency anaemia (IDA) in athletes is rare.
Assessment of iron status in athletes
This often requires blood tests as well as the athlete filling out a food diary. Iron levels could be low if a test is carried out soon after strenuous exercise, in states of chronic inflammation or infection or in dehydration. In a blood test several markers should be assessed – iron levels, serum ferritin, transferrins, serum transferrin receptors and TIBC – however the reference values for these markers vary from lab to lab and there are no clear cut off values that have been defined for different demographics in an athletic population. Based on a blood test iron deficiency can be divided in to 3 stages:
Stage 1
Depleted iron stores – a blood test will present reduced TIBC and low serum ferritin.
Stage 2
Early functional iron deficiency – a blood test will also present decreased transferrin saturation and increased serum transferrin receptors.
Stage 3
Iron deficiency anaemia – a blood test will present reduced haemoglobin and mean cell volume (MCV). Even a small decrease in haemoglobin of 1-2g /mL can decrease performance by 20%
Iron sources
Iron is found in many foods, both animal and plant foods. Animal foods contain haem iron, which is highly available for absorption, plant foods contain non-haem iron which is less bioavailable. Iron absorption in athletes is affected by numerous things. If there is any gastrointestinal damage from overuse of NSAIDs or from Coeliac disease iron absorption will be affected. Iron absorption can be enhanced by consuming vitamin C containing foods or drinks at the same meal, such as a glass of orange juice. Good food sources of vitamin C include broccoli, Brussels sprouts, cabbage, peppers, strawberries, oranges and kiwi fruit. Iron absorption is also enhanced in the presence of vitamin A and protein containing foods.
Iron absorption can be disrupted by:
• A high carb diet that athletes are often recommended. A large consumption of pasta and rice for example that contain phytates disrupts iron absorption in the bowels.
• Calcium supplements taken at the same time as iron supplements,
• A fear of saturated fat and red meat means that consumption of iron containing foods can be low.
• Tannins in tea and coffee bind with iron and reduce absorption.
Iron supplements
Iron supplements can be administered in athletes with low serum ferritin levels. Who needs iron supplements would be judged on a case by case basis based on a medical history, blood tests and a food diary but recovering from Iron deficiency anaemia can take several months using high doses of iron supplements. A dose of 100-300mg of elemental iron per day would be required in this time period. It is preferable to use absorbable forms of iron such as ferrous fumerate, ferrous gluconate and ferrous sulphate
Summary for healthy iron level in athletes
• Have your blood tested twice a year to look at iron levels, serum ferritin, transferrins, serum transferrin receptors and TIBC.
• Rule out Coeliac disease in those with low iron, functional iron deficiency and iron deficiency anaemia.
• Consider iron status in fatigue, lethargy and low immunity.
• Eat red meat several times a week
• Consume vitamin C rich foods with the red meat – broccoli, Brussels sprouts, cabbage, peppers, strawberries, oranges and kiwi fruit
• Consume vitamin A rich food as well – butter, eggs, carrots, squash, sweet potato.
• Reduce grain intake – get carbs from vegetables as well as grains
• Reduce tea intake or at least drink tea away from meals
• Take calcium supplements away from main meals and iron supplements if you have low iron levels.
• A dose of 100-300mg of elemental iron per day taken with some vitamin C containing food.
References
Dean, V. (2010). Prevention, detection and treatment of iron depletion and deficiency in athletes. In Clinical Sports Nutrition 4th Edition. Louise Burke and Vicki Deakin.
