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Iron deficiency anaemia as a cause for athletic decline

Many athletes complain of hitting a training plateau which tend to compromise their progress. Often, this plateau is due to fatigue caused by overtraining and inadequate nutrition (athletes require a special diet).  Workouts that had formerly been easy can become progressively harder to complete. Even taking additional days off doesn’t necessarily do the trick.

Very often the cause is iron-deficiency anaemia, one of the most common nutritional deficiencies among athletes (especially female athletes).


Early onset of fatigue during exercise is a common complaint among athletes, especially endurance athletes. Overtraining, stress, or many other external factors can be the cause of fatigue, however, fatigue fatigue is attributable to a lack of iron in the blood, a condition known as anaemia.

Iron is a major element of the body's red blood cells or haemoglobin, and carries oxygen to various muscles and tissues for use during aerobic activity. Recent research indicates that endurance training creates an additional demand for iron that many athletes are unable to meet. In fact, 75% of women aged 18 to 55 don't eat enough iron-rich foods, so depletion of iron stores is inevitable. This is especially prevalent during menopause.

An iron deficiency will reduce sports performance due to the fact that oxygen isn't transported effectively to the operational muscles, which leads to a accumulation of lactic acid. Symptoms of iron-deficiency anaemia include:

  1. nausea

  2. frequent infections

  3. pale, washed-out appearance

  4. Anxiety

  5. Irritability or a low feeling

  6. Angina

  7. Constipation

  8. Sleepiness

  9. Tinnitus

  10. Mouth ulcers

  11. Palpitations

  12. Hair loss

  13. Fainting or feeling faint

  14. Depression

  15. Breathlessness especially during exercise

  16. Burning and Twitching muscles


Over 50% of female endurance athletes and 45% of male endurance athletes have depleted iron stores, which suggests that in order to prevent anaemia, a dietary intervention may be advisable. 

Because iron-deficiency anaemia is more widespread in athletes, it's vital to monitor iron status. This can be done by checking various biochemical markers (see table below), as well as examining the diet. Iron-deficiency anaemia happens in three stages, with stage 3 having the most damaging effect on athletic performance.

Studies show that the majority of iron-deficient endurance athletes have a stage 1 deficiency; meaning iron reserves in the body are depleted. Stage 1, or none-anaemic iron deficiency, is diagnosed when serum ferritin (the chemical storage form of iron) levels drop below a blood level of 12 ug/dl.


If stage 1 iron deficiency is undiagnosed for a few months it may develop to stage 2, in which red blood cells and consequent oxygen transfer are decreased leading to reductions in exercise ability. Stage 3 characterized by intense fatigue, diminished physical capacity and decreased athletic performance, and is detected by insufficient haemoglobin and a low concentration of red blood cells.

Biochemical Markers of Iron Status

Depleted iron stores can arise as a result of several factors, which include an inadequate diet and/or absorption of iron, intense endurance training, and in female athletes due to excessive blood loss through menstruation.

Nutrition and Absorption

Insufficient dietary iron intake may be the primary reason why endurance athletes develop iron deficiencies. The recommended daily allowance (RDA) of iron from food and supplements is 18 mg/day for women and 8mg/mg for men aged 19 and up. Iron needs increase during pregnancy and lactation, and decrease at menopause.

At present, there aren't any official special iron recommendations for athletes, but recent research suggests that needs may be higher due to iron loss during intensive training. Nonetheless, both the general population as well as athletes, on average, fall below the current RDA for iron, thereby increasing the risk for depleted iron stores and reducing training performance.

Another challenging factor to take into account is that only approximately 15% of ingested iron is absorbed – generally speaking, absorption depends on three factors:

  1. type of iron ingested (plant or animal based)

  2. meal composition

  3. the individual's iron status


Iron can be found in many types of foods -- both animal and plant origin:

  1. Red meat, pork and poultry

  2. Seafood

  3. Beans

  4. Dark green leafy vegetables, such as spinach

  5. Dried fruit, such as raisins and apricots

  6. Iron-fortified cereals, breads and pastas

  7. Peas


However, it's a well-established fact that iron found in animal products, otherwise known as heme-iron, is better absorbed than iron found in plant products -- up to 20% higher.

For this reason, vegetarian athletes have a greater risk for iron deficiency (as well as Vitamin B12 deficiency), even if total iron intake is the same. Despite this, some 40%of competitive female endurance athletes avoid meat.

Iron absorption can be boosted by consuming foods which rich in vitamin C (i.e., citrus fruit, bell peppers, Guavas, Kale, kiwi etc.). On the other hand, iron absorption may be diminished by up to 50% by several chemicals which are contained in certain foods, including tannic acid found in tea and coffee, food additives such as phosphate found in soft drinks, and food preservatives. Iron absorption is also decreased with higher than necessary consumption of other minerals (i.e., zinc, calcium). However, keep in mind that iron absorption depends on the severity of iron depletion, meaning those with iron-deficiencies will absorb more iron than those without iron deficiency.


Red blood cell count and haemoglobin concentration has been shown to be less in athletes compared with non-athletes, which may support the theory that exercise creates an extra demand for iron that exceeds its intake. Tests show that daily dietary iron needs may be as high as 41 mg during intense endurance training. The term "sports anaemia" is commonly used to describe iron depletion and subsequent drop in haemoglobin to anaemic levels. Sports anaemia occurs in athletes who dramatically increase their training intensity, and the symptoms are most of the short-lived.

Additional iron needs during training may be related to a phenomenon known as haemolysis, where red blood cells are damaged from the constant pounding of running. The repeated foot contact with the ground causes red blood cells to rupture and release haemoglobin, some of which is excreted by the kidney and therefore appears in the urine. Runners might lose 1.0 to 1.5 mg of iron from haemolysis, which means that additional iron consumption is vital in order to prevent anaemia symptoms.

Loss of iron through sweat is also a likely cause increased demand for iron in athletes. Though iron loss through sweat may be insignificant, these losses can add up over prolonged athletic endurance events such as Ironman, triathlons or marathons. It's estimated that approximately 0.3 to 0.4 mg of iron is depleted per litre of sweat whilst exercising.


Menstrual blood loss is another of the principle factors responsible for iron depletion in females. Female athletes who menstruate regularly lose iron-rich haemoglobin during their period, with average iron losses ranging from 5 to 45 mg depending on the heaviness and length of the individual menstrual cycle. This iron loss requires an additional 5 mg of dietary iron per day.

Treating iron-deficiency anaemia

Iron-deficiency anaemia should be treated with therapeutic doses of supplemental iron.  There are two forms of dietary iron, “heme” iron and “non-heme” iron. Heme iron is iron bound to haemoglobin (the oxygen transporting protein in blood); non-heme iron is not bound to haemoglobin. Heme iron is the most efficiently absorbed form of iron. The absorption rate of non-heme iron supplements, such as ferrous sulphate and ferrous fumarate, is 2.9% on an empty stomach and 0.9% with food. This is much less than the absorption rate of heme iron, as found in liver, which is as high as 35%. In addition, heme iron is without the side effects associated with non-heme sources of iron, such as nausea, flatulence, and diarrhoea.

Despite the superiority of heme iron, non-heme iron salts are the most popular iron supplements. One reason is that even though heme-iron is better absorbed, it is easy to take higher quantities of non-heme iron salts so that the net amount of iron absorbed is about equal. In other words, if you take 3 mg of heme iron and 50 mg of non-heme iron, the net absorption for each will be about the same. The best form of non-heme iron is ferrous succinate. Consult a healthcare professional before taking iron supplements. Because high doses of iron can cause nausea, diarrhoea and constipation, it is recommended to increase the dosage from once a day to three times a day until tolerance is established.

The length of time for iron supplementation will vary -- check with a health professional. Blood work is generally repeated every four to six weeks, but typically it takes approximately eight weeks for endurance performance improvement.15

While supplemental iron is beneficial for individuals with inadequate iron reserves, athletes with normal iron status are advised against iron supplementation. Iron overload can cause serious health issues.

Ensuring Adequate Iron Reserves

Maintenance of good iron reserves requires emphasis on iron-rich diet. To improve iron intake, follow these tips:

  1. Eat lean cuts of beef, pork, and lamb three or four times a week. Liver has higher concentrations of iron.

  2. Choose iron-fortified breads and cereals.

  3. Don't drink coffee or tea with every meal, particularly if you're prone to anaemia. Substances found in these drinks interfere with iron absorption.

  4. Combine vegetarian and animal sources of iron.

  5. Eat iron-rich foods with vitamin C to boost absorption.

Frequent monitoring of iron levels in the blood, including biochemical and nutritional analyses, is recommended for all endurance athletes, especially vegetarians, in order to prevent iron-deficiency anaemia and to assure optimal health and maximal athletic performance.

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