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Iron and Performance

About Iron

There is approximately 3.5-4.5 grams of iron stored in the body.  About two-thirds of this is found in hemoglobin and the rest is distributed among the liver, spleen and bone marrow with small amounts in myoglobin.  Iron deficiency is popular among certain individuals but the following are early warning signs that health professionals can use to identify a possible iron deficiency that warrants receiving follow-up blood testing:

While there are many roles that iron plays in the body (immune and neural function, thyroid hormone metabolism, erythropoesis and part of mitochondrial oxidative enzymes), the most important role for exercise performance is as a component of the protein hemoglobin.  One red blood cell contains about 250 million hemoglobin molecules thus a higher level of iron can mean a higher aerobic capacity and better performance due enhanced oxygen delivery to muscles.

Iron stores can be hard to maintain for some active individuals because the typical iron absorption from eating a Western diet ranges from 10-35%.   Following a vegetarian diet provides much less iron absorption, from 1-20%.  It is beneficial to choose foods higher in iron but the absorption rates are still low which makes obtaining adequate iron from food extremely difficult for those suffering from iron deficiency. 

Additionally, there are many inhibitors to the absorption of iron that can decrease the absorption rate even more.  These include calcium, zinc (although maybe not when consumed as food and not as a supplement), bran and soy products, phytates and fiber found in whole grains and nuts, and tannins found in coffee and tea.  Individuals who have Celiac disease or Crohn’s syndrome may also have lower rates of iron absorption due to the affects of these disorders on the gastrointestinal system.  To combat iron inhibitors, it is important to add more foods that promote iron absorption.  These include meat, fish, poultry, brussels sprouts, green and red bell peppers, broccoli, potatoes, tomatoes and other vitamin C rich foods.

There are two types of iron in foods: heme and non-heme.  Heme iron has a higher absorption rate and can be found in animal products such as beef, chicken, shrimp, fish, oysters and sardines.  Non-heme iron has a much lower absorption rate and is found in vegetable sources such as enriched cereals, blackstrap molasses, pumpkin seeds, beans, tofu and lentils.

Low food absorption rates top the list as one of the factors associated with iron deficiency.  Depending on the stage of iron deficiency, it is extremely difficult for some individuals to improve their iron stores through food alone due to information presented thus far.

Signs and Symptoms of Low Iron Stores

Many individuals will try to self diagnose themselves with low iron stores based on how they are feeling and while that may or may not prove 100% correct, their body signs will provide the health professional a clue as to what may be happening.  One of the most common symptoms associated with iron deficiency anemia is fatigue that worsens with exertion during exercise.  This can be quite difficult for a person to define as there are many definitions of fatigue based on the workout that is being done.  However, if an individual experiences normal fatigue throughout the day and it is not worsened with exercise, the cause is likely not iron deficiency; however, a full iron panel blood test should be done regardless to rule out iron deficiency.  Aside from fatigue during exercise, there are a host of other symptoms of iron deficiency anemia including the following:

The first step in the process of assisting someone with possible iron deficiency is sending them to a physician who specializes in working with athletic individuals to receive a full iron blood work analysis.  Normal ranges on a laboratory data sheet will vary depending on the geographical location and laboratory.   It is very important to note that just because a person may be normal for that laboratory range, it does not mean that they are not low in iron stores.  It is highly recommended that the health professional track trends with iron stores blood testing since one person may be low when it is in fact still in the normal range on the data sheet.

Laboratory Testing

As mentioned previously, a full laboratory blood iron panel is the best way to assess iron status.  There are a number of clinical markers that are used to explain iron status, and below is a brief description of these markers in order to better understand the laboratory data sheet:

Serum ferritin, one of the most common clinical markers used in the assessment of iron deficiency, does not decrease until levels of iron become too low to support demands.  For example, if the body is using and excreting more iron than it is receiving from food, the ferritin level will slowly decline. If an iron deficiency is suspected based on having some of the signs and symptoms mentioned above, the person should receive a full complete blood count (CBC) and iron stores test done immediately. 

Prior hydration status in the days leading up to blood work testing can affect the results.  Having blood drawn in a dehydrated state can cause higher values for some iron markers; therefore, it is recommended that individuals have this blood test done in a hydrated and somewhat rested state since there is also an inverse relationship between training load and ferritin levels.  As training load increases, serum ferritin decreases.  Depending on the stage and if identified early enough, iron deficiency can be managed effectively.

Iron Deficiency Stages

There are three stages of iron deficiency, all with different blood marker identifiers.  Stage one is termed iron depletion and is the most mild form of iron deficiency.  Normally, serum ferritin levels will be decreased and if detected early enough, this stage can be easily managed through food and in most cases, does not require supplementation.  Stage two is termed iron deficiency without anemia which is characterized by a low serum ferritin, a decrease in percent transferrin saturation and an increase in total iron binding capacity.  This also can be treated with food if caught early enough but supplementation may be needed.  Stage three, termed anemia, is the most serious of the stages and includes all of the above mentioned blood clinical markers in addition to a decrease in hemoglobin.  This almost always requires an aggressive supplementation protocol.  There are various types of anemia which may alter the treatment protocol including:

Improving Iron Stores


As mentioned previously, normal laboratory ranges for iron markers will differ based on the laboratory and geographical location thus it is important to obtain a baseline test in a normal living environment and not during a short-term visit to another location, especially if at altitude. Iron stores can be improved, if identified early and an aggressive treatment protocol is followed, in about six to eight weeks (usually only for stage 1 and 2).  An individual should account for this in their exercise program by reducing training load in the initial phases of the treatment process.


While it is possible to improve iron stores through a well structured eating program, some individuals may need to introduce an iron supplement depending on their stage of iron deficiency and their eating habits.  Non-vegetarians must consume more heme iron containing foods while vegetarians have more of a challenge since non-heme iron containing foods constitute the majority of their iron intake and have a lower absorption rate.   The following charts represent the Recommended Dietary Allowance and Tolerable Upper Intakes of iron as references.

Fig. 1   Recommended Dietary Allowances

Age Males
9-13 years 8 8 n/a n/a
14-18 years 11 15 27 10
19-50 years 8 18 27 9
51+ years 8 8 n/a n/a

Fig. 2  Tolerable Upper Intakes

Age Males
1-13 years 40 40 n/a n/a
14-18 years 45 45 45 45
19+ years 45 45 45 45


In a perfect world, supplementation would not be necessary but for individuals with low iron stores, it may be a necessity.  For those with clinically diagnosed iron deficiency anemia, it is important to continue eating foods high in iron with using an iron supplement on a daily basis. 

Taking an iron supplement without justification from a blood test interpreted by a physician or sport dietitian may lead to iron overload which can cellular damage and even death.  This condition, termed hemochromatosis, is caused by a genetic defect that affects the ability to regulate and absorb iron in the body.  About one in two-hundred individuals are genetically predisposed to it thus the importance for blood testing for iron stores becomes even more important.

Taking iron supplements does not fall into the “more must be better” category and can have very dangerous side effects.  In fact, iron becomes less absorbable when taken in higher quantities.  Supplemental iron may also cause certain gastrointestinal (GI) distress such as constipation.  There are many types of iron supplements on the market but one type in particular has a higher absorption rate (up to 75%) thus lower quantities of it are required.  It is called ferrous bisglycinate with the trade name ferrochel, and is found in stand-alone form and in multi-vitamins.  The additional benefit is that it has very few to no negative GI side effects and does not affect other mineral absorption.


Replenishment of iron stores typically takes about 6-8 weeks and in cases of the first stage of iron-deficiency, supplementation may not be necessary.  Iron-rich foods should be the main emphasis for any individual at risk for iron deficiency along with having frequent blood testing done.  Iron supplements should only be used after clinical iron stores blood testing has been completed and under the guidance of a qualified sports physician or sports dietitian.

References and Recommended Readings

  1. McClung, JP et al.  Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron status, physical performance, and mood.  Am J Clin Nutr, 90(1): 124-131. 2009.
  2. Ostojic, SM & Ahmetovic, Z.  Weekly training volume and hematological status in female  top-level athletes of different sports.  J Sports Med Phys Fitness, 48(3): 398-403.  2008.
  3. Peeling, P. et al.  Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones.  Eur J Appl Physiol, 103(4): 381-391.  2008.
  4. Venderley, AM & Campbell, WW.  Vegetarian diets: nutritional considerations for athletes.  Sports Med, 36(4): 293-305. 2006.
  5. Hinton, PS & Sinclair, LM.  Iron supplementation maintains ventilatory threshold and improves energetic efficiency in iron-deficient nonanemic athletes.  Eur J Clin Nutr, 61(1): 30-39. 2007.