Though a few athletes try to artificially achieve a high red blood cell count, the typical marathoner needs to ensure that she or he doesn’t have a low red blood cell count or low iron stores. Low iron levels may be the most prevalent nutrition deficiency in Western marathoners. 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. Although anemia is more detrimental, both of these conditions can negatively affect your running performance.
Runners tend to have lower iron levels than do sedentary folks for many reasons: increased blood volume, low iron intake, foot-strike hemolysis, iron loss through sweat and urine, and iron loss through the gastrointestinal (GI) system. For marathoners, the iron losses tend to be higher than for those doing shorter races, primarily because of higher training volumes. Let’s look at each of these factors.
Increased Blood Volume. Endurance athletes have more blood than do normal people. This adaptation allows the stroke volume of the heart to increase, which allows
O2max 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 doesn’t increase as much as the blood volume, then hemoglobin concentration will decrease and may incorrectly indicate an iron deficiency. This is a natural phenomenon that any sports doctor will recognize but that your local general practitioner may not.
Low Iron Intake. Many endurance athletes have low iron intakes. Low iron intake can be a problem for vegetarians and runners who eat red meat less often than once a 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. Runners who don’t eat meat can obtain sufficient iron through dietary sources but only by carefully selecting their foods. Enette Larson-Meyer ’s book, Vegetarian Sports Nutrition, is a good resource for more information on proper nutrition for vegetarian athletes.
Foot-Strike Hemolysis. Foot-strike hemolysis is the breakdown of red blood cells when the foot hits the ground. Foot-strike hemolysis is potentially a problem for marathoners who run high mileage on asphalt or are heavier than most runners.
Iron Loss Through Sweat and Urine. 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. For marathoners living in the south or training through the summer in preparation for a fall marathon, sweat may be a significant source of iron loss. More research is needed to determine the magnitude of iron losses in sweat.
Iron Loss Through the GI System. Loss of iron through the GI tract (primarily the stomach or large intestine) is a problem for some marathoners. In a 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.
All the preceding factors in combination make it important for marathoners to monitor their iron intake and their iron levels. The highest risk occurs in premenopausal female runners, whose iron intake often doesn’t meet their needs.
If you have low iron, first, you’ll be dragging. Your heart rate may be elevated, and your enthusiasm for running will have sunk. These symptoms tend to come on gradually, however, so you may not suspect that you have low iron levels until they’ve had a large impact on your training. You can confirm your suspicions only with a blood test. You should find out your hemoglobin level (the iron in your red blood cells) and your serum ferritin level (your body’s iron stores).
Normal hemoglobin concentration ranges from 14 to 18 grams per deciliter (g/dl) of blood for men and 12 to 16 g/dl of blood for women; for an endurance athlete, the lower end of normal should be extended by about 1 g/dl because of his or her larger blood volume. For a male marathoner, then, a hemoglobin level between 13.0 and 13.9 g/dl could be considered in the low end of the normal range and would be similar to a level of about 14.0 to 14.9 g/dl for an untrained man who doesn’t have a marathoner ’s elevated blood volume. Similarly, a female marathoner with a hemoglobin level between 11.0 and 11.9 g/dl would have a lower than optimal level that would be similar to a level of about 12.0 to 12.9 g/dl for an untrained woman.
Normal reference serum ferritin levels are 10 to 200 nanograms per milliliter (ng/ml) for women and 10 to 300 ng/ml for men. Conflicting schools of thought exist on the relationship between ferritin levels and running performance. One opinion is that ferritin levels aren’t directly related to performance, but if your ferritin level falls, eventually your hemoglobin and performances will decline too. Low ferritin, therefore, can be viewed as an early warning sign.
The other school of thought is that ferritin reflects the iron stores the body can use to make enzymes for oxidative energy production; therefore, they have a direct impact on performance. The optimal level of serum ferritin seems to differ among individuals. Dick Telford, PhD, of the Australian Institute of Sport, has found that the performance of some runners seems to be affected when their ferritin levels drop below 50 ng/ml, whereas others perform fine if their ferritin levels remain above 25 ng/ml. Telford says that even with iron supplementation, some runners have difficulty raising their ferritin levels above 50 ng/ml.
David Martin, PhD, who has been in charge of testing elite distance runners for USA Track and Field since 1981, says that in his experience with runners, training and racing performances are usually affected when ferritin levels drop below 20 ng/ml. When those athletes increase their ferritin levels above 25 ng/ml, they experience a rapid turnaround in performance. These experiences indicate that a ferritin level between 25 and 50 ng/ml may be normal or low depending on your individual physiology, but a ferritin level below 25 ng/ml is a definite red flag for a runner.
According to the National Academy of Sciences’ 1989 recommended daily allowances (RDAs), premenopausal women need about 15 milligrams of iron a day, whereas men and postmenopausal women require 10 milligrams of iron a day. Iron requirements haven’t been established for high-mileage runners, so all that can be said with confidence is that marathoners need at least the RDA. As with any mineral, too much iron can be a health hazard. In fact, the typical American man is more likely to get an iron overload than to be iron deficient.
As with other running problems, such as injuries, the best strategy is to avoid low iron in the first place. Good food sources of iron include liver, lean meat, oysters, egg yolk, dark green leafy vegetables, legumes, dried fruit, and whole-grain or enriched cereals and bread.