Running and Rusting

By Peter Pfitzinger |

You head out the door for an eight-mile run. Right from the start, your energy level is down, and your legs feel heavy. After 2 miles of uncharacteristic drudgery, you stop-then jog and walk home.

What’s the problem? Could be low iron. Iron is vital to running performance. Despite this importance, many runners do not monitor their body’s iron levels. Even many physicians do not understand the complete role of iron for endurance athletes.

To find out the latest on iron and running, the Pfitzinger lab report talked with two experts in the field, Dr. E. Randy Eichner, Chief of Hematology at the University of Oklahoma Health Sciences Center, and David Martin, Ph.D., of the Department of Cardiopulmonary Science at Georgia State University. Dr. Eichner has worked with distance runners and other athletes for over 15 years, and Dr. Martin has been Physiology Chair in charge of testing elite distance runners for USA Track and Field since 1981.

Why do runners need iron?

Iron is necessary for production of hemoglobin in your red blood cells. Hemoglobin carries oxygen from the lungs to the muscles. If your hemoglobin level is low, less oxygen reaches your muscles, and your VO2 max and racing performances suffer. In addition, iron is a component of many other substances in the body, such as enzymes in your muscle cells for aerobic energy production.

With iron deficiency anemia, your iron stores are gone, and your hemoglobin level is reduced. With iron depletion, on the other hand, your iron stores are low but not gone, and your hemoglobin is still normal.

Why do runners tend to have lower iron levels?

Runners tend to have lower iron levels than sedentary folks due to the following factors: increased blood volume, low iron intake, foot strike hemolysis, iron loss through sweat and urine, and iron loss through the gastrointestinal (GI) system. Let’s look at each of these factors.

#1: Endurance athletes have more blood than normal people-which allows the stroke volume of the heart to increase-which allows VO2 max to increase. This is a good thing. The iron in a runner’s red blood cells, therefore, is diluted in a greater volume of blood. If the runner’s red blood cell mass does not increase as much as the blood volume, then hemoglobin concentration will decrease, and may incorrectly indicate an iron deficiency.

#2: Many endurance athletes have low iron intakes. Low iron intake is a problem for vegetarians, and for those runners who eat red meat less than once per week. The typical high carbohydrate, low fat, low cholesterol runner’s diet often includes little or no red meat. Red meat contains heme iron, which is more easily absorbed than plant sources of iron.

#3: Foot strike hemolysis is the breakdown of red blood cells when the foot hits the ground. While foot strike hemolysis is not a big problem for most runners, if you are larger than average or run high mileage on asphalt, it could be a factor for you.

#4: A relatively small amount of iron is lost through sweat and urine, but for high mileage runners training in hot, humid conditions, this iron loss may add up. More research is needed to determine the magnitude of this problem.

#5: Loss of iron through the GI tract (primarily the stomach or large intestine) is a problem for some athletes. In a recent study following 11 runners over a competitive season, GI bleeding was evident in 17 of 129 stool samples after training, and in 16 of 61 stool samples after racing. The bleeding is fairly minor each time, but there may be a cumulative effect over years of running.

So, the cards are stacked against runners in terms of iron. We tend to take in less, and lose more, than our sedentary peers. The highest risk occurs in pre-menopausal women runners, whose iron intake often does not meet their needs.

How do you know if you have low iron?

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