CYCLING PERFORMANCE TIPS
Last updated: 11/1/2015
(including iron metabolism)
A few definitions:
- blood volume - The circulating volume of red blood cells and serum. The blood
volume of the average adult is about 10 pints (or 5 liters).
- serum (plasma) - The liquid portion of the total blood volume. Serum is composed of water,
electrolytes, albumin, and other proteins (such as antibodies).
- hemoglobin - The molecule in red blood cells that binds oxygen. In the lungs, where oxygen concentrations are high, hemoglobin will bind oxygen. When the blood cells enter a
low oxygen environment (in the capillaries -- particularly in muscle fibers involved in exercise), hemoglobin releases bound oxygen. Iron is one of several critical components for hemoglobin production (if the total body iron levels are low, the hemoglobin levels will be low)
- red blood cells (rbc) - The cells which contain the hemoglobin molecule.
- whole blood - Red blood cells and serum. 10 pints in the average adult.
- hematocrit (hct) - An expression of the percent of whole blood that is just red blood cells. In
a normal adult the hematocrit is 40 to 45% of the total blood volume,
thus a normal hematocrit is 40 - 45%.
- hemoglobin concentration (hgb) - The actual amount (weight) of hemoglobin (in gms) present in 100 grams
of whole blood. It is just another way to think of the oxygen carrying capacity of a
certain volume (pint, cc, etc.) of blood. It is often used as an alternative to the hct. to quantify the oxygen carry capacity of whole blood.
A normal hemoglobin is 14 to 15 grams percent (14 to 15 grams of hemoglobin per 100 grams of whole blood).
- ferritin - The iron transport protein in the serum that supplies iron for red blood cell production. In anemias resulting from low
total body iron stores (thus one of the raw materials for blood production is in short supply),
the ferritin will be low.
ACQUIRED ANEMIA IN THE ATHLETE
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:
- Dilutional or pseudoanemia (sports anemia)
- Exertional hemolysis
- Iron deficiency anemia
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:
- impact (mechanical trauma)
- turbulence in the blood vessels
- acidosis in the working muscle
- elevated temperature in the working muscle
This is not a problem seen in cyclists but it is included here
for completeness. How might one go about treating it?
- the size of the red blood cells in circulation is increased (the Mean Corpuscular Volume or MCV measures the amount of hemoglobin per rbc and is increased as young or new RBCs are bigger in size than older RBCs)
- the reticulocyte count is elevated (reticulocytes are the new RBCs formed in the prior few days and have a unique morphology on microscopic exam of the blood)
- the haptoglobin level is decreased (haptoglobin is a serum protein that scavenges hemoglobin
released from ruptured blood cells) as it combines with the free
hemoglobin released from the destroyed rbcs into the serum.
- eliminate other causes of hemolytic (broken blood cell) anemias
such as medications, sickle cell trait, and other inherited fragile rbc syndromes.
- mitigate impact issues with soft shoes, orthotics, and by running on soft surfaces
- slow incremental increases in training (which seem to help)
C) Iron Deficiency Anemia
A low blood count (anemia) from iron deficiency is the most common true (versus
dilutional - see above) anemia in athletes.
It is most often due to a poor oral intake of iron with a component of
increased iron loss (menstrual loss in women, and rarely bleeding from the GI tract
see A and
B for more detail). Iron deficiency anemia is more
common in female athletes who have a higher incidence of eating disorders (poor
intake) with the added component of iron loss associated with monthly menses.
Iron is a necessary for the production of hemoglobin in red blood cells - and is also a
component of many metabolic enzymes throughout the body. It is absorbed
from the food we eat and is regularly lost through the kidneys and intestinal tract
(as colon lining cells are shed). When absorption and loss of iron are in balance, you
have enough iron stored in your body to support red blood cell production for about
The diagnosis of iron deficiency can be suspected when an exam of the blood cells reveals a small
rbc size (when there is not enough iron, new blood cells, lacking adequate hemoglobin, are smaller than normal), and
confirmed by finding a low ferritin.
The recommended daily dietary iron intake for an adult male is ~ 8 mg per day, whereas for a menstruating, non-pregnant females it is higher (~ 18 mg) to account for increased basal iron losses via menstruation. The bioavailability of iron in food depends on the source. Absorption of iron is greatest for iron in the hemoglobin and other iron containing enzymes in red meats (15% to 35%), as compared with 2% to 20% of the non heme iron present in vegetables and grains (vegetarians are at increased risk of becoming iron deficient.)
If an athlete (especially a vegetarian or woman) is worried about becoming iron deficient,
options for prevention include:
But there are risks of unneeded supplementation, especially if larger doses are used. Too much absorbed iron can lead to iron overload disease (hemochromatosis) with significant irreversible and negative impacts on the heart, liver, and pancreas.
- increasing the intake of meat (if not a vegetarian)
- the use of vitamins with a small amount of iron (no more than 15 mg per day).
---A daily multi vitamin which contains 15 mg of iron is low risk and may give
you peace of mind. However, with a regular diet, it is generally unnecessary.
- the vitamin should be separated from calcium supplements, fiber supplements, and caffeine -
all of which can impair absorption
- vitamin C can aid absorption, so drink that glass of orange juice when you take
Treatment of iron deficiency when there is a low blood count (anemia) is not controversial.
- consider ferrous sulfate 325 mg one to three times a day - start slow with one tablet per day as
some athletes develop indigestion or bowel problems (both constipation and diarrhea) on iron
supplements, and these symptoms are dose related.
- recheck a blood count after two to four weeks of oral to assure the iron is being
absorbed (the blood count should be rising at this point) . Some people are poor absorbers (no rise in blood count is seen) and may need intravenous iron.
- it will take two to three months to replete total body iron stores - then switch to a prevention program. Do not continue the large treatment doses as the risk of iron overload disease is significant.
ROLE OF IRON WITHOUT ANEMIA
a) Low Ferritin Without Anemia
You can become deficient in iron
(your total body stores of iron are below normal) before the blood count begins
This has led to speculation that a low total body iron state without anemia may
contribute to poor performance as iron is found in many enzymes (besides red
blood cells) that are involved in aerobic metabolism (mitochondrial oxidative
enzymes, cytochromes of the electron transport chain). In this scenario, the
serum ferritin would be low, but the blood count may not yet
have started to drop. It is speculated that these might be athletes with a ferritin at the low end
of the "normal" range. Women are a special case. Although the normal ferritin
for women is 15, many of the women whose blood studies were used to set
the normals for women may have had low iron stores
from chronic menstrual blood loss. Thus 15 may indicate mild iron deficiency and
the true normal for women may be nearer to 25.
Nonetheless, all the controlled studies to date fail
to show a benefit of iron supplements UNLESS the iron deficiency is associated with
anemia (references - 1, 2,
This conservative recommendation to treat only when anemic is not only based on
the lack of evidence as to benefit, but also as there are risks of over treatment.
Higher is not better, when it comes to
serum ferritin levels. If one tries to push iron supplements in the face of a normal
ferritin - remember 25 is normal for some athletes - the risk of iron overload disease
is significantly increased. And animal models have shown that
iron overload can lead to a decrease in exercise performance.
b) Oral iron as a performance enhancer
The final question - does increasing your iron intake - without a low blood iron/ferritin or anemia -
provide a performance benefit. To quote from a review of
the literature, "Iron supplementation can raise serum ferritin
levels, but increases in ferritin concentration, unaccompanied by increases in hemoglobin
concentration, have not been shown to increase endurance performance.
This series of articles is a good example of how these "myths" start - and then are perpetuated. First, the original article
which, I feel, misrepresents the conclusions of the referenced study: Iron Levels and Altitude.
Taking supplements may increase the benefits of thin-air training. Which it was
then reprinted for cyclists in Bicycling:
This Common Supplement Could Help You Ride Better at Altitude"
This was a pretty strong claim so I thought I'd look for more details
in the original article in PLOS.
Although the PLOS article was quoted as supporting improved athletic performance at altitude with
iron supplements, as far as I can determine it only found that IRON DEFICIENT athletes
incorporate more substrate (iron) into their blood cells if they were given supplements - which
makes sense. They need iron (even at sea level as they are iron deficient), so given iron plus the
stimulus of altitude, it is only reasonable to assume that they will absorb more of it. And
as iron is in many enzymes (along with iron in blood cells), one might also expect some performance
improvement (non heme level related) in the iron deficient athletes as well. And of course there is
no evidence that the iron deficient group actually improved performance - only that the blood cell mass increased and thus it was assumed they would perform better as well.
So in my reading, this is a great example of an unfounded interpretation in the lay press that will
lead to iron supplementation abuses by athletes who have adequate iron stores, and expose those looking
for that performance edge to the toxicity of iron supplements.
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
- If your ferritin and % iron saturation are low, you need iron. So getting the blood
tests are step 1.
- If you have normal iron levels, the chemo may be depressing red blood cell production
and you may benefit from epo. As long as your hct is less than 50% you may be able to do
sanctioned races while on it, but ask. You are in special circumstances with the chemo and
might need a waver.
- If the blood test show that you are iron deficient, I'd suggest you use the supplements.
It will take too long to get levels up to normal with red meat alone, and you want to feel
back to you normal more quickly than that. Once your iron levels are back to normal,
you should be able to maintain with diet (even meat free) alone. But an occasional supplement
every other day would provide a little insurance from the effects of an unbalanced diet.
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):
- serum iron 103 (normal > 109)
- serum transferrin 234 (normal >109)
- serum ferritin 92 (normal >67)
- hct (blood count) 45 (normal 47)
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 (ie, 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.
- The blood count is not diagnostic of iron deficiency (anemia would help to confirm suspected iron deficiency based on borderline blood iron levels, if present).
- The serum iron is not a reliable indicator of iron deficiency.
- The serum ferritin says "normal body iron stores" but if it was done a day after vigorous activity it might be falsely elevated into the normal range.
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
Roadbikerider.com 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
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
- Gabe Mirkin, M.D. "It is extraordinarily dangerous for a healthy man to take extra
iron unless he suffers a deficiency. While women lose iron regularly through
menstruation, men lose iron only through bleeding. No man should ever take iron unless
his blood test, called ferritin, shows that he is low on iron. Excess iron can deposit
in the liver to cause cirrhosis, pancreas to cause diabetes, and the heart to cause a
heart attack. Iron is an oxidant that damages tissue. High levels increase risk for
- Lisa Weissmann, M.D. "I am a hematologist (physician specializing in blood
disorders) as well as an avid road bike rider. The gentleman in the story had developed
iron deficiency anemia from donating blood over a long period of time. For him, the
cause of his anemia was iron deficiency, and therefore iron in his case was essential
to restore him back to normal. However, anemia can be from a multitude of causes, and
iron will not help unless it happens to be iron deficiency. Moreover, iron, by itself,
in people who are not iron deficient or anemic, will have no benefit in terms of performance."
- Paul Pagoff, M.D. "Iron deficiency [in men] almost never occurs because of diet
deficiency. In men with real iron deficiency the cause is likely blood loss of some sort,
including blood donation. If there is no clear explanation then cancer in the intestinal
tract needs to be ruled out."
- Steve Weeks, DDS. "Iron is needed for hemoglobin production, as indicated in the
article. However, iron is highly conserved in normal males, and dietary requirements for
replacement are quite small. Men who have low iron levels as reflected by low hemoglobin
or hematocrit should not simply take iron supplements, but should receive medical
evaluation for the cause of the deficiency. Some possibilities are gastric ulcer, colon
cancer or other form of gastrointestinal bleeding. Less commonly, it is decreased
production of red blood cells in the bone marrow owing to the influence of drugs or disease.
You did say, correctly, that people starting on supplements should consult their physician.
However, it might bear repeating that iron deficiency, especially in men, could be
serious and that, as tempting as it is to pop over to the drug store for iron pills,
a physician should be involved."
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.
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