Blog post by Elissa Rosen, MD, CEDS
Iron deficiency is common in athletes. Nearly half of females who exercise may experience iron deficiency.  While females are at higher risk for iron deficiency due to monthly loss of blood with menstruation, male athletes can also suffer from it. The International Olympic Committee 2009 Consensus Statement on periodic health evaluation of elite athletes even recommended routine screening for iron deficiency.  Please note, unless otherwise specified, the term iron deficiency in this article solely refers to low iron and not resultant anemia, or low red blood cells. This article is also focused on adult athletes and the information discussed may not apply to children.
What is iron? Why is iron important?
Iron is a mineral that has several important roles in the body including energy metabolism, oxygen transport, and acid-base balance.  Iron is found mostly within red blood cells and therefore necessary for their production. Red blood cells transport oxygen throughout the body and are filled with proteins called hemoglobin. Each hemoglobin molecule contains iron. Oxygen picked up in the lungs binds to the iron inside hemoglobin and then is carried all over the body to supply oxygen to organs and tissues.
Where do we get iron from?
Iron comes from our diet. Dietary iron can be classified into heme iron and non-heme iron. Heme iron is found in meat, poultry, and fish. Red meat contains about three times as much iron as both poultry and fish making it one of the richest sources of dietary iron. Heme iron is absorbed by the digestive tract about twice as well as non-heme iron. Sources of non-heme iron includes fruits, vegetables, and iron fortified foods. Vitamin C assists with the absorption of non-heme iron in the digestive tract so mixing foods rich in vitamin C with non-heme iron containing foods can increase the amount of iron the body absorbs. 
Why are athletes at risk for iron deficiency?
Athletes need more iron than the general population. Iron is lost through sweat, skin, urine, the gastrointestinal (GI) tract, and menstruation. Exercise, particularly high intensity and endurance types, increases iron losses by as much as 70% when compared to sedentary populations. Athletes lose more iron due to heavy sweating as well as increased blood loss in the urine and GI tract.* Red blood cells also break down more quickly in those who exercise. The mechanical force of a footstrike during endurance running, for example, can increase the destruction of red blood cells in the feet, leading to a shorter red blood cell life span.
Female athletes are at even higher risk for iron deficiency as compared to males due to monthly blood loss associated with menstruation. Athletes may also be at risk for iron deficiency due to insufficient dietary iron intake. Remember, the body is not very effective at absorbing dietary iron. Athletes, particularly menstruating female endurance athletes, need to be extremely mindful of iron intake in order to meet their bodies’ demands. Those following a strict vegetarian or vegan diet can be at even higher risk for iron deficiency due to the decreased absorption of non-heme iron found in plants and fortified foods.
What are the symptoms of iron deficiency?
Because iron is necessary for oxygen transport and energy metabolism, both of which are critical for fueling aerobic exercise, endurance athletes can experience a decline in exercise capacity and VO2 max, the maximal amount of oxygen the body can use, with iron deficiency. As iron deficiency becomes more severe, the body cannot make a sufficient number of red blood cells and anemia, meaning low red blood cells, develops. Athletes with iron deficiency anemia will generally have more pronounced symptoms than those with iron deficiency alone. Athletes may experience the following symptoms as a result of iron deficiency, particularly with anemia: weakness, general fatigue/exhaustion, decreased exercise performance, increased heart rate and shortness of breath during exercise, headaches, and dizziness.  Another more unusual feature of iron deficiency is the development of pica or cravings for things that are not generally meant to be eaten such as ice chips or even clay, dirt, or paper! A craving for ice chips is actually pretty specific to iron deficiency, so any athletes out there who find themselves wanting to eat a lot of ice should definitely have their iron levels checked.
How is iron deficiency diagnosed?
Iron deficiency is diagnosed through blood tests. The most useful of the typical iron study panel is ferritin, which is a marker of iron stores. Traditionally, levels less than 15 ng/mL are considered diagnostic for iron deficiency.  Most labs report the normal ferritin range between 15-150 ng/mL for females and 15-300 ng/mL for males. Even if a lab printout states the ferritin is ‘normal,’ it may actually be too low depending on the athlete, the type of exercise they perform, and their current physical symptoms. In the sports nutrition community, there is no clear ferritin goal for athletes. Given that certain athletes may need more than double the iron than less active populations, a reasonable ferritin goal would be at least 30-40 ng/mL, if not higher. Every athlete’s physiology and training demands are different, so ferritin goals vary person to person and can be individualized. If a ferritin is dropping significantly during the course of a training cycle, this can also be indicative of developing iron deficiency and the need to intervene, even if the ferritin is within what is generally considered a normal range. It is also worth mentioning that ferritin levels can quickly increase when the body is under stress so results may be falsely high during periods of active infection or inflammation.
The other traditional iron panel tests can be useful in distinguishing iron deficiency from poor iron utilization states. A complete blood count (CBC) measures the levels of red blood cell in the body and determines whether or not someone is anemic. Markers of red blood cells in a CBC are hemoglobin and hematocrit. Of note, iron deficiency is only one of the many causes of anemia.
How is iron deficiency treated?
Consultation with a sports dietitian is recommended for athletes with iron deficiency. A sports dietitian can perform a thorough dietary review and make recommendations for ways to increase iron intake. Replenishing iron levels through dietary means is always preferable to taking an iron supplement. For some, iron supplementation through oral means (pill or liquid) may be necessary. Oral iron comes in many formulations that are generally equally effective as long as taken regularly. Milk, coffee, and tea can interfere with iron absorption so should not be consumed along with the iron supplement.  A recent study suggests that taking oral iron every other day may actually increase iron absorption.  The dose, frequency, and duration of iron supplementation can be guided by a sports dietitian or a physician.
Unfortunately, oral iron can be difficult to tolerate due to side effects. Up to 70% of people taking oral iron report GI side effects such as nausea, vomiting, stomach upset, or constipation. ** Ways to make oral iron supplements more tolerable include taking them with food (though this may decrease its absorption), taking them every other day, or changing the formulation. Anecdotally, sports dietitians our clinic has worked with find that a specific iron product called Blood Builder is much better tolerated than standard iron supplements, though there is no directed scientific evidence to back this up.*** For those who cannot tolerate or have not responded to oral iron, intravenous (IV) iron can be given under the guidance of a physician. It is NEVER advised to make a self-diagnosis of iron deficiency. If an athlete is concerned that they might be iron deficient, they should get blood tests to confirm the diagnosis. Taking iron supplements in the absence of iron deficiency can lead to iron overload, which is very dangerous. There are also certain people that are genetically hardwired to absorb more iron and are at risk of iron overload even in the absence of high iron intake.
Iron deficiency in athletes, particularly of the endurance variety, is common. Increasing iron in the diet is an important step in avoiding iron deficiency. Even so, our bodies only absorb a small portion of the iron we eat. Working with a sports dietitian can help an athlete find ways to increase dietary iron intake and absorption. Iron deficiency can make an athlete feel exhausted and decrease exercise capacity, but is easy to diagnose and generally not complicated to treat.
* The blood lost in the urine and stool from exercise described here is not visible to the athlete. If an athlete ever sees frank blood in their urine or stool, they should seek medical attention right away for a thorough evaluation.
** Oral iron supplements can turn stool black. This can be very anxiety provoking in those unaware of this side effect as black stool is usually an indication that there is blood in the stool and may signal a GI bleed.
*** Neither myself nor the Gaudiani Clinic has any affiliations or financial involvements with Blood Builder.
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