Why is iron deficiency so common in active individuals?

Iron deficiency is the most common nutritional deficiency in the world, across all population cohorts. This is an issue that is noted as especially common within the sporting world, despite active individuals generally being very health conscious with generally good diets. Let’s take a look at some of the factors at play regarding this phenomenon and how a sport and exercise nutrition coach can help. First, we’ll outline the functions of iron markers and their appropriate levels is needed, so you can understand what we are dealing with.

Haemoglobin (Hb)

The protein molecule that carries iron and oxygen in our bodies. This is the most widely used marker for testing for anaemia (deficiency of haemoglobin).  For adult females, levels are typically 12-16g/dL and for males, they range between 14-18g/dL. Given its function, Hb is very important for any aerobically dominant sport.

Haematocrit (Hct)

This measures the thickness of the blood. Red blood cells are large, the more we have, the thicker our blood will be. Females range normally from 36 to 44%, whereas men are typically between 40 to 50%. Values above 50% can be used as a cut-off for blood doping or suspicion of doping.

Ferritin

This is your backup iron store, and this will be the most telling read of iron deficiency. Ferritin levels drop if there is a mismatch between iron output and intake over an extended period of time. If stores are low but Hb is normal, an individual is ‘iron deficient’, but not anaemic, and may not have any symptoms. Ferritin values of less than 35ug/L indicate iron deficiency, less than 20ug/L refers to iron deficiency non-anaemia, and less than 12ug/L is the diagnostic threshold of anaemia. For active individuals, we want your ferritin levels above 50ug/L.

MCV

Mean corpuscular volume, this is a measure of how big your red cells are, they will normally range between 80-100fL. Values below this indicate microcytic anaemia, within the normal range is normocytic, whereas values above this range refer to macrocytic anaemia. Most microcytic anaemia is caused by thalassemia or iron deficiency, resulting in smaller red blood cells. Whereas, macrocytic anaemia is usually due to B vitamin deficiencies, namely B12 or folate. A normal MCV value with low ferritin or haemoglobin tells us that you are simply iron deficient.

TIBC & Transferrin Saturase

These markers essentially reflect how hard your body is working to absorb iron from your gut, and this may be higher in those who are deficient. Normal ranges are 240-450mcd/dL for TIBS. The higher this number, the harder your body is working to absorb iron from your intestines. Those with the genetic condition hemochromatosis may have high values ofo TIBC/Transferrin saturase.

How much iron do I need?

Now it is important to look at and assess what our iron requirements actually are for context purposes. Male adults need about 8mg per day, females need about 14.8mg per day and those who are plant-based (i.e. not consuming any haem iron) need approximately 2.2 times the previously mentioned numbers.

“A steak has about 6-8mg per palm-sized fillet and a portion of broccoli has about 2mg per serving.”

The difference between animal and plant-based sources comes down to absorption. Non-haem iron (plant-sourced) is absorbed at rates of 2-20% whereas haem iron (animal-sourced) is absorbed at rates of 20-40%. It’s important to maintain good supplementation and nutrition when training on a vegetarian or vegan diet.

Let’s look at several factors now that influence this picture, and why up to 11% of male and 35% of female athletes suffer from iron deficiency (Sims et al., 2002), the first two factors are relevant for everybody:

• We lose 2mg of iron every day through intestinal cell recycling
• Female athletes lose 2mg per day during their periods
• We lose iron in our sweat (it’s fair to say that athletes generally sweat more than pretty much anybody else) with rates ranging from 0.4 – 1.2L/hr in sweat losses
• Foot strike haemolysis – Striking the ground with your heels whilst running can result in red blood cells rupturing prematurely. As this red squishy part of your foot is literally full of blood, running-based sports are more relevant here (Lippi, 2012)
• Hepcidin bursts. – Our spleen releases hepcidin in response to inflammation and exercise. Hepcidin has an evolutionarily developed role of blocking iron absorption in the gut when inflammation is present. More intensive exercise, exercise that is done fasted or whilst following a low-carb diet, will typically cause 3 times more hepcidin to be released (Badenhorst, 2015)
• Disordered eating, eating disorders and restrictive diets are unfortunately not uncommon in sports settings. This often results in the diets of an athlete being nutritionally inadequate, with iron deficiency often popping up in this context

Symptoms of low iron

You might not be aware if you have progressing iron deficiency, as ferritin levels (your backup stores) drop asymptomatically towards depletion. This drop can lead to anaemia whereby you no longer have enough iron to support oxygen transport, which is very symptomatic. With this in mind, it is prudent for those who are physically active to get repeated blood assessments done. An athlete should have a rudimentary target of 50ug/L for their ferritin count.

If you get to the point of anaemia whereby aerobic capacity is compromised, it takes three months on high-dose iron supplements to bounce back. Symptoms to watch out for include:

• a pale appearance
• angular cheilitis
• thinning hair
• brittle nails
• restless legs
• general fatigue

If you notice any of these symptoms it may be time to get that blood test. An important point of note to finish on – you should never take an iron supplement unless you have been diagnosed with iron deficiency or anaemia. It is potentially hazardous and will be totally ineffective in improving athletic performance.

References

Sims ST, Mackay K, Leabeater A, Clarke A, Schofield K, Driller M. High Prevalence of Iron Deficiency Exhibited in Internationally Competitive, Non-Professional Female Endurance Athletes-A Case Study. Int J Environ Res Public Health. 2022 Dec 10;19(24):16606. doi: 10.3390/ijerph192416606. PMID: 36554486; PMCID: PMC9778947.

Lippi G, Schena F, Salvagno GL, Aloe R, Banfi G, Guidi GC. Foot-strike haemolysis after a 60-km ultramarathon. Blood Transfus. 2012 Jul;10(3):377-83. doi: 10.2450/2012.0167-11. Epub 2012 May 17. PMID: 22682343; PMCID: PMC3417738.

Badenhorst CE, Dawson B, Cox GR, Laarakkers CM, Swinkels DW, Peeling P. Acute dietary carbohydrate manipulation and the subsequent inflammatory and hepcidin responses to exercise. Eur J Appl Physiol. 2015 Dec;115(12):2521-30. doi: 10.1007/s00421-015-3252-3. Epub 2015 Sep 3. PMID: 26335627.