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  Latest update: 11/7/2021

Anemia (including iron deficiency)

A few definitions:


There are multiple potential reasons for the development of anemia (a low blood count i.e. hct or hgb) in athletes, including acute blood loss from an accident as well as nutritional deficiency states. We will review three of the more common, acquired anemias found in athletes. Specifically:

A) Dilutional Anemia

This is not a true anemia in that total body hemoglobin (the total amount of hemoglobin being circulated by the cardiovascular system) is normal. The anemia reflects the fact that the amount of serum (liquid portion of the blood volume) has increased in this condition and as a result "diluted" their red blood cell concentration. In essence, the total blood volume may have increased slightly (to 10.5 pints for example), but the number of red blood cells circulating is the same as in the normal (original) 10 pints - thus the concentration of hemoglobin per pint (or cc) and hematocrit decrease slightly.

It is speculated that with work outs you become slightly dehydrated (which means your total blood volume decreases below normal - now 9.5 pints instead of the "normal" 10), the body senses this deficiency in the kidney (where the renin/angiotensin system kicks in) and in the pituitary (which increases ADH hormone release). Both of these lead to fluid retention (overcompensation) when you are able to drink adequately again.

The degree of dilutional anemia correlates with the intensity of exercise and is in the range of 5 - 20% below your hgb concentration (not a 20% drop in your absolute hgb or hct.) With moderate exercise, the hgb may decrease 0.5 gms, and in elite athletes the hgb may be as much as 1 gram lower than the athlete's "normal" range. Dilutional anemia may be seen within a few days of starting or intensifying exercise, and will correct back to normal within a few weeks of stopping exercise. It is high on the list of potential reasons for anemia when the ferritin is normal in the face of newly noted anemia, and can be confirmed if the hct or hgb returns to normal when the athlete stops exercising for one to two weeks.

Teleologically, are there potential benefits of a dilutional anemia? In the short term (before the body can produce additional red blood cells in response to the demands of exercise) it is a rapid way for the body to increase the blood volume and thus the cardiac stroke volume resulting in more blood being pumped through the lungs and muscle circulation per beat. It also decreases blood viscosity, which may be important to blood flow at the capillary level during exercise.

b) Exertional Hemolysis

This is also referred to as "march anemia" or "foot strike" anemia. Although it was at one time felt to be related to direct trauma to the red blood cells as they were traumatized by the foot hitting the ground with running or long marches, it can also seen in non impact sports such as swimming, rowing, and weight lifting. Interestingly it has never been reported in basketball or baseball players. As it is seen most frequently in runners, local trauma from the "foot strike" remains the primary suspect. It is most likely a combination of several factors: The triad that helps make the diagnosis is: This is not a problem seen in cyclists but it is included here for completeness. How might one go about treating it?

C) Iron Deficiency

Iron is an essential component of the oxygen carrying red blood cell hemoglobin molecule as well as cell enzymes involved in the production of ATP. If the body's total iron stores fall below normal, these energy production enzymes are impacted before hemoglobin production is impacted. This explains why fatigue and a decrease in athletic performance can occur an athlete's red blood count falls. This is a common dilemma for an athlete pushing their training - is fatigue from overreaching or less likely from iron deficiency.

But just adding an iron supplement to eliminate that possibility has risks as too much iron is toxic to normal liver, heart, and pancreas cells.

Dietary iron, from plant and animal protein, replaces the 1 to 4 mg daily iron lost through the kidneys and intestinal tract (via shedding colon lining cells). A person who stops taking in any iron at all (poor diet or absorption problems) has enough iron stores to support enzyme and red blood cell production requirements for about one year. So any imbalance, for example a new fad diet or low level blood loss, would take many months to reach the point where iron deficiency would impact performance.

Iron is one of the most difficult minerals to absorb from our diet. The efficiency of iron absorption varies between individuals as well as being dependent on the food source. We absorb 15% to 35% of the iron in animal protein versus 2% to 20% of the iron in vegetables and grains.

The recommended daily allowance for iron in an adult male is 8 mg per day and 18 mg/day for menstruating non-pregnant females.

Iron deficiency is more common in athletes than in non athletes. And is the most common true (versus dilutional - see above) anemia in athletes. It is most often the result of poor oral intake with the additional iron loss burden of menstrual blood loss in women. It is even more likely in elite athletes who commonly adopt unusual diets as they work to maintain competition weight. For those interested, this is an easy to understand summary with additional details.

Although there has been speculation on increased loss from the intestinal tract, this appears to be a greater risk in the runner than cyclist. Here are two links for more detail A and B. Red blood cells are smaller than normal (microcytosis) suggest an iron deficiency diagnosis. When there is not enough iron, new blood cells, lacking adequate hemoglobin, are smaller than normal. The next step is additional blood work. Blood test are indirect measures of body iron stores. If there is still a question, a bone marrow exam, which directly quantifies iron stores in the bone marrow, is the gold standard. Let's review the iron physiology again.

Iron absorbed from the intestine (this step can be bypassed with IV iron) binds to the protein transferrin which then transports iron to cells where it is used directly in cell repair or to the bone marrow where it is stored as ferritin.

The earliest change in a developing iron deficiency is a decrease in ferritin levels. Next the amount of transferrin that contains iron (expressed as a percent) increases. And finally the lack of iron begins to affect the production of hemoglobin and the blood count starts to fall (anemia). This in turn impacts the ability of the cells to carry oxygen to exercising muscle cells.

This article summarizes blood test options with examples of results in iron deficiency. If there are conflicting results, the blood iron level and transferrin are not as useful as the ferritin levels - so if they give conflicting result, the ferritin is generally considered the better of the two. But even for ferritin levels, blood levels can occasionally be misleading. Plasma ferritin is what is called an “acute phase reactant” which means levels may be elevated following vigorous physical activity or in an individual with an inflammatory illness. Thus, determination of ferritin levels should be postponed in athlete who have recently completed an acute bout of exercise training or in those with acute febrile illness). (underlining is mine). So to be accurate, a serum ferritin should be checked after a few days of rest (or at best only on days with mild activity. For those interested in more discussion of iron tests, this website is a nice resource.

The bigger challenge is deciding if a fatigued athlete who is not anemic might be in the early stages of iron deficiency and might benefit from iron supplements. The challenges of using a blood test to decide are:

  1. "Normal" ranges are fuzzy, especially at the lower limits. Many people considered as normal for the purposes of establishing these normal range may actually be mildly iron deficient.
  2. Transferrin and ferritin levels may vary with mild infections or other inflammatory processes.
  3. As cellular energy enzymes may be more sensitive to low iron than hemoglobin production, fatigue can be a symptom of iron deficiency even with a normal blood count.

There is usually no question as to the diagnosis of iron deficiency when a fatigued athlete with a normal blood count has a ferritin level below 20 micrograms/L or when their blood hemoglobin levels are low and the ferritin is now less than 12 micrograms or the transferrin saturation below 16%. The group that is problematic has a ferritin levels that is technically normal but at the bottom end of the laboratory's normal range.

The recommended daily iron intake for an adult male is ~ 8 mg/day, and for a menstruating, non-pregnant females ~ 18 mg to replace iron losses from menstruation. The bio-availability of dietary iron is greatest for red meats (15% to 35%) compared to 2% to 20% for the iron in vegetables and grains. That is why vegetarians are at increased risk of becoming iron deficient.

If an athlete (especially vegetarians and women) is worried about becoming iron deficient, options for prevention include:

Treatment of iron deficiency when blood test have confirmed low iron stores as the reason for the anemia or fatigue is not controversial. But for pure prevention, there are risks associated with excessive doses in supplements. Too much absorbed iron can lead to iron overload disease (hemochromatosis) with its negative and irreversible impacts on the heart, liver, and pancreas.

For confirmed iron deficiency:

What about those with a suspected low iron (ferritin) but no anemia - those athletes with a ferritin at the low end of the "normal" range. A comment here about the ferritin level in women. Although a normal ferritin for women is said to be lower than men, many of the women whose blood studies were used to set normalranges may have really had low iron stores from chronic menstrual blood loss. My guess is that the numbers below a lab's normal range for men should apply to women as well.

All studies to date fail to show a benefit from iron supplements UNLESS the iron deficiency is associated with anemia (references - 1, 2, 3). The most recent meta analysis of multiple studies confirms the lack of benefit in the absence of anemia. This has led to the conservative recommendation to treat only when anemic, especially with the significant risks of over treatment. Not only is there that risk of organ damage, animal models have shown that too much iron also decreases exercise performance.

My take aways:


When you donate blood, you will be giving 1 pint (about 10% of your total blood volume). In doing so you will temporarily decrease the oxygen carrying capacity of your blood by 10%. Your body will compensate by replacing the fluid volume within 48 hours, and the hemoglobin will be synthesized (replaced) in a week to 10 days. Until your hemoglobin has been replaced, your cardiovascular system will adapt by increasing your heart rate for any level of exercise - thus increasing the amount of oxygen delivered to the cells during any period of time.

You won't notice much of a change in performance on moderate rides. However if you did intervals, you would notice a decrease in performance until the hemoglobin is replaced. It is a good idea to give blood on a rest day and keep the next few workouts light. And be sure to wait at least 2 weeks before entering a performance event. Over time, repeated blood donation might lead to iron deficiency. Use the prevention measures mentioned above to decrease your risk.


Q. I am a 27 year old road-racer. I had a seizure in my first race of the season. In the end I was diagnosed with brain cancer, had a tumor removed, went through radiation, and am now on chemo for the next 12 months. I am going to race this year even through it, as a swift finger toward the cancer, and a sign of hope and strength for myself. The big effects of the chemo is low hemoglobin and hematocrit levels. Here is the big question. I've been vegetarian since I was ten, and now I am wondering if maybe I should start eating red meat. Other thoughts? - MN


Q. I was recently queried by a reader about their laboratory results and the possible need for iron supplements. Values of interest (and I'll leave off units of measurement):

A. In answering this question I am going to use direct quotes from a very nice summary article I recently ran across.

1. Why should an athlete care about iron deficiency? Because low body iron stores will impact performance.

The oxygen carrying capability of blood is directly related to the hemoglobin molecule concentration which is in turn is directly related to iron availability (a key component of hemoglobin production). And there is a speculative component that iron deficiency may impact muscle enzyme levels directly (iron is part of many enzyme systems). In addition "...impairment of exercise capacity in anemic individuals may reflect more than reduced oxygen transport. Subjects with low hemoglobin concentrations also manifest a decrease in blood viscosity and reduction in systemic vascular resistance, effects that increase cardiac work and strain circulatory function."

2. Is this athlete anemic? Questionable

Although suggestive, these numbers (hct 47) do not support a clear diagnosis of anemia. Blood counts do vary a few points from blood draw to blood draw, so a hct of 45 on repeat might be 47. And individuals have their own "normal" that may always be a bit lower or higher than the population averages. In addition, to quote "......Borderline low hemoglobin concentrations with normal ferritin concentrations are sometimes observed in athletes...."

3. Does this athlete have iron deficiency (early, without anemia)?

This is where it gets murky. Blood test are indirect measures of body iron stores. The gold standard is a bone marrow exam that directly assesses body iron levels (iron is stored in the bone marrow). The blood iron level and transferrin are not as useful as the ferritin levels, so if they give conflicting result, the ferritin is generally considered the better test for diagnosis of body iron levels.

"Serum iron levels demonstrate a great deal of variability over time (both circadian and rate of release from the reticuloendothelial system), bear no reliable relationship to ferritin concentration, and cannot be expected to accurately reflect body iron status."

"Ferritin circulating in the blood stream accurately reflects body iron stores and serving as a reliable marker of iron deficiency. A value of 1 ng/mL of ferritin corresponds to about 5 to 9 mg of stored iron."

But a qualifier here - "...It is important to recognize that plasma ferritin is an acute phase reactant, and levels will be consequently elevated following vigorous physical activity or in an individual with an inflammatory illness. Thus, determination of ferritin levels should be postponed in athletes in an inflammatory state (i.e., those who have recently completed an acute bout of exercise training or in those with acute febrile illness)." This means that one could be iron deficient with a low serum ferritin and yet see it falsely elevated into the normal range after a bout of strenuous activity.

So to increase its predictive value, a serum ferritin should be checked after a few days of rest (or at best only mild or rest day activity.

The answer to the original question? It is unclear with the information available.

Next steps? Take a few days off and repeat the blood count and the serum ferritin. If the athlete cannot do that, then a bone marrow exam would give the only clear answer.

Should they just take iron "just in case"? There are definite risks to this approach as iron can be toxic to the liver, heart, and pancreas if taken at high doses for long periods of time. Again, to quote: "Expert opinion is in agreement that, considering these possible risks, athletes with normal ferritin levels should not take iron supplements."

There was a spirited discussion of iron deficiency in cyclists on recently. I, along with a number of other health care people responded. I'll reprint portions that summarize nicely the key issues in considering iron supplements for anemia and iron deficiency in athletes.

The article: "Supplement Worth Re-considering"

"Last week's piece about the potential benefit of iron supplements ("A Supplement Worth Considering") sparked lots of feedback, including e-mails from six medical professionals. In general, the docs expressed great concern about men taking extra iron. Although we included a warning about that and the wisdom of consulting a physician first, they either overlooked the caveat or wanted to emphasize it. Important comments from four doctors are below."

The bottom line, perhaps, was provided by this e-mail from a roadie who asked that his name not be used: I am not an expert on this but do have an experience regarding the blood issue. My cardiologist, also a bike racer, found out that I donated blood regularly. His immediate response was that sport cyclists should not donate blood without a serious review of the pros and cons. "Riders may be better off reducing their blood donations than taking iron supplements."

A portion of this material was excerpted from a talk given at the 10th annual Sports Medicine Conference held at Sun Mountain Lodge 1/2004 by Kimberly Harmon, MD, Sports Medicine Clinic, University of Washington.

All questions and suggestions are appreciated and will be answered.

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