Why are low iron levels so common in runners?
About three years ago the Journal of Adolescent Health published a study that may be alarming to endurance athletes. Israeli researchers reported finding high levels of anemia (or low red blood cell count) and iron deficiency (a common cause of low red blood cell counts) in young male military recruits. Levels of anemia and low iron were already above normal, at 18 percent and 15 percent, respectively, at the start of training, and increased to 50 percent and 27 percent after six months of training.
The Reuters news agency picked up the story and distributed it under the headline, “Intense Exercise May Lower Your Blood Count.”
If this were true, it is cause for concern, as anemia not only causes troublesome symptoms such as weakness and fatigue, but it also sabotages exercise performance. But is it really true? The idea that intense exercise may, as a normal outcome, reduce the body’s capacity to perform intense exercise seems rather absurd. Chances are that in your experience, intense exercise increases your fitness instead of causing symptoms of anemia. Yet this Israeli study is not alone in finding high rates of anemia among athletes.
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The fact of the matter is that the connection between exercise and iron deficiency anemia, if there is one, is mysterious. Medical scientists do not have it figured out. As a recent review by Australian researchers stated, “Commonly, athletes are diagnosed as iron deficient, however, contrasting evidence exists as to the severity of deficiency and the effect on performance.”
One source of confusion is the fact that there are many ways to measure anemia. The two general categories of measurement, alluded to above, are red blood cell count and iron status. In the past it was believed that anemia was rampant among athletes because they often exhibit low blood hemoglobin concentrations. But an important 1992 study by South African researchers dismissed this phenomenon as a harmless “pseudo-anemia” caused by the expansion in blood volume that results from exercise training — a beneficial adaptation that increases the body’s thermoregulatory capacity and its capacity to transport oxygen to the working muscles.
The balance of evidence does indicate that iron deficiency is more common in endurance athletes than in the general population; however, it seems that only in a small minority of cases do iron-deficient endurance athletes exhibit symptoms of anemia. A 1996 study by Turkish researchers found no link between changes in iron status and performance in a group of female athletes. This may indicate that iron deficiency in endurance athletes does not always have the same meaning in athletes as it does in non-athletes, much as low hemoglobin often means different things in the two populations.
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Iron deficiency and anemia appear to be more common among runners than other endurance athletes, among female runners than male runners, and among high school and college female runners than older female runners. A 2008 study by researchers at the University of Minnesota found that 89 percent of the members of a women’s college cross country team were anemic at one time or another during the season.
Experts have proposed various explanations for the higher rates of iron deficiency and anemia seen in these populations. They include iron loss through sweating, destruction of red blood cells on footstrike in running, and iron depletion associated with tissue inflammation. My personal belief, based on real-world experience rather than research, is that iron deficiency and anemia are most common among young female runners because of low intake of iron-rich foods associated with internal and external pressure to maintain a low body weight.
In other words, I speculate that low iron levels are common among young female runners primarily because they take in less iron, not because their bodies lose or destroy more iron. I find it extremely improbable that exercise training would stimulate literally thousands of different physiological adaptations that serve to increase exercise capacity (not to mention general health) with one great exception: accelerated iron depletion resulting in anemia.
Confused? Well, so are the experts. But for all the confusion about the science of anemia, avoiding it is usually pretty easy. First, make sure you’re getting at least 10 mg of iron daily if you are a man or a postmenopausal woman, 15 mg daily if you are a premenopausal woman. Second, as an endurance athlete you should be sure to get your iron status checked at each annual physical exam, or anytime you experience persistent fatigue with no obvious cause.
If it is found that you have low iron levels but you lack any symptoms of anemia, iron supplementation may not be necessary — follow your doctor’s recommendation. But if you have low iron and symptoms of anemia, doctor-supervised supplementation may leave you feeling — and performing — like your old self again.
About The Author:
Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.