Q. I’ve heard a lot about iron-deficiency anemia being quite common in long distance runners.  Why is this?  I heard that it had something to do with the constant pounding on pavement, but I had no idea whether this was true or not. If a runner is somewhat anemic, is it best to cut down on the miles or is taking an iron supplement sufficient?

A. Great question. There are a couple types of anemia that runners can get: iron-deficiency anemia and microangiopathic hemolytic anemia.

Before I discuss those, however, I should mention that there is a pseudo-anemia in some runners that is probably more common than either of these real anemias. Athletes tend to have higher plasma volume than non-athletes. As the body adapts to the higher oxygen needs of exercise, one of the things it does is pull more fluid into the blood (good idea, because that gives the heart a bigger stroke volume, aids in sweating and staves off dehydration). If you measure the hemoglobin in such a patient, it will appear low – but that’s only because it’s diluted out by a bigger plasma volume. The red cells look normal (normochromic, normocytic, minimal poikilocytosis) on the blood smear. Usually this type of anemia is mild, with no more than a 1 gram drop in hemoglobin. Any drop over 1 gram means you need to pursue other causes.

Iron-deficiency anemia can occur in runners for two reasons: bad diet and increased iron loss. Many runners have a high-carb, low-fat diet, with much of their protein coming from non-meat sources. Iron in red meat is more easily absorbed than iron from plant sources, so over time, a dietary iron deficiency may develop. A very small amount of iron is lost in sweat, which probably makes for a negligible loss in regular runners, but if you’re an endurance runner, that can add up over time. The red cells in iron-deficiency anemia are hypochromic and microcytic. In addition, there is usually increased anisocytosis (as each wave of new red cells comes out, they have less iron, so they end up smaller than the previous wave) and poikilocytosis (for some reason, you often see skinny oval-shaped red cells – these are called elliptocytes – in iron-deficiency anemia). To make sure that you’re dealing with an iron defiency, though, you need to do iron studies to see if the patient is truly iron deficient.

You are correct about the pounding on the pavement! If you think about it, every time you slam your foot down on the pavement, you compress tiny capillaries in your feet, which can lead to red cell fragmentation (microangiopathic hemolytic anemia). In normal day-to-day life, this fragmentation is very, very minimal, and if you did a blood smear, you wouldn’t see any red cell fragments. In runners, however, there is a greater amount and severity of foot-pounding, so this can add up to more fragmentation. Things that predispose to this fragmentation are logical: poor or worn-out shoes, a higher percentage of running on asphalt or concrete (as opposed to a nice cushy track), greater body weight, and a heavier foot strike. If the fragmentation is severe enough, some of the hemoglobin will be excreted in the urine. This phenomenon is called “march hemoglobinuria” in reference to its occurrence in soldiers who march for long periods of time. To diagnose microangiopathic hemolytic anemia, you need to do a blood smear to look for fragments (also called schistocytes).

So what should you do about all this? It depends on which type of process is causing the anemia. To figure this out, you need at least a CBC (which will have the Hgb, MCV, and MCHC, among other indices), and preferably also a blood smear (which will confirm the reported lab values and show you whether there is poikilocytosis or not). If the hemoglobin is no more than a gram under normal, and the red cells are normochromic and normocytic, and there are no fragmented red cells, then the anemia is likely a pseudo-anemia due to dilution, and no treatment is necessary.

If the red cells are hypochromic (low MCHC) and microcytic (low MCV), and there is increased anisocytosis and some elliptocytes on the blood smear, then iron studies are warranted to rule out iron-deficiency anemia. The treatment for iron-deficiency anemia is iron supplementation – but you need to make sure there isn’t another cause for the iron deficiency first (especially in men or post-menopausal women, in whom you need to rule out a slow GI bleed due to colon cancer).

Finally, if you see schistocytes on the blood smear, it is a microangiopathic process, which in an otherwise-healthy endurance runner is most likely due to running-related fragmentation. Changing shoes and running surfaces should help; if it is a severe anemia, I suppose you’d need to cut down on miles, but just try telling an endurance runner that. A search for other causes should be undertaken in any other type of patient, because there are some pretty serious causes of microangiopathic hemolytic anemia.

Image credit: Eleftheria G