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When Iron Man Runs Low

Have you ever felt fatigued, drained, convinced that your iron levels are low. Then been to the GP who checked your bloods… only for them to come back normal. No answers or solutions found… just ongoing tiredness.

The truth is there are many reasons why people may feel more tired than usual, and the first port of call should be a full check up by your GP. Although exercise is good for you in many ways, it can actually deplete your body’s iron and leave you feeling more tired than usual. The way that this occurs can be quite surprising.

Why we need iron?

Most of people know that iron is involved in the formation of our red blood cells. Haemoglobin, an iron containing compound, is essential for transferring oxygen in your blood from the lungs to the tissues. In muscles, myoglobin functions as an oxygen storing unit, providing oxygen and energy to the working muscles. Myoglobin contains haeme and is responsible for the red colour of our muscle and iron rich red meats. In fact, across our whole body iron is an essential compound which allows every single one of our cells to access its stored energy (to create ATP via the electron transport system). Also, our iron levels play an important part in controlling our susceptibility to infection and immune function.

Where we store iron?

In the western world, most people have approximately 4-5 grams of iron. Approximately 70% of this is found in Haemoglobin and used for our oxygen carrying capacity. About 25% is stored in a protein called ferritin that can be found in most cells but in abundance in our liver, spleen and bone marrow. Ferritin plays a significant role in the absorption, storage and release of iron. As the storage form of iron, ferritin remains in the body tissues until it is needed to make more red blood cells. Doctors measure ferritin as an indicator of our body iron levels as we will discuss later.

Why we lose iron?

Although dietary iron is poorly absorbed, the body conserves its iron stores carefully, reabsorbing most of the iron released from the breakdown of red blood cells. As a result, the body normally loses only 1 to 2 mg of iron per day. This loss is restored by the iron absorbed in the from dietary sources. However, some people are at a higher risk of developing anaemia than others. For example, women with heavy menstrual losses and pregnant women. However, people who exercise are another high risk group that are often forgotten.

So why does iron loss occur in people who exercise?

  • Loss in sweat. Believe it or not we sweat out iron. Various studies have shown that this however is only in the tens of micrograms, even with marked volume loss of sweat, so this is not one to worry about.
  • Gastrointestinal bleeding. This is by far where the biggest loss occurs. Although losing traces of blood through our GI tract is normal, runners have shown to lose anywhere from 0.75 to 1.1 mg/d, which is twice the normal average. This is because strenuous exercise can cause damage to the lining (endothelium) of the whole GI tract from stomach to large bowel. In some cases this can present as visible blood in the stool.
  • Foot strike haemolysis. The repetitive pounding we give the surface when we run or play sport actually destroys red blood cells which in turn causes iron levels to reduce.
  • Anti–inflammatory drugs. People who exercise may rely on anti-inflammatories more to help with there aches and pains. Non-steroidal anti-inflammatory drugs (NSAIDS) also disrupt the protective lining of prostagladins in the stomach causing bleeding.
  • Apparent anaemia. This phenomena often in athletes because they have a larger plasma volume (i.e the fluid that the red blood cells bath in). This has the affect of diluting the red blood cells, creating a similar picture to anaemia on blood tests.

Iron requirements and replacement

Athletes have dietary iron requirements that are 1.3 to 1.7 times higher for athletes than non-athletes. This is to make up for the extra losses described above, but also regular exercisers usually have more red blood cell (RBC) mass, meaning higher iron needs. As we exercise, our body is continuously regenerating and growing raising iron requirements.

To measure iron status, doctors often use reference values to determine whether ferritin levels are normal. A low ferritin level can be considered less than 15 mg/L. However, due to the higher iron requirements for exercisers this reference range can be misleading. People who exercise should have a lower threshold for the treatment of low ferritin levels or anaemia. For instance, some professional footballers are often treated for iron deficiency when ferritin levels dip below 50-70 ug/L, which would be considered normal to most doctors.

The best way to replace low iron levels is through diet, and I will discuss this in another blog. However, if you do a lot of exercise, it is always worth letting your doctor know how much before you have a blood test to investigate anaemia. After all, a long distance runner putting in 50 miles/week will have different iron requirements to the average patient.

I hope you now understand a little more about the iron in your blood. Look out for on of my future blogs on the best way to replace iron by adapting your diet!

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