Hematocrit and Iron in Athletes
Cyclists are always looking for an edge, and that leads many to a visit to the doctor for a blood test. One of the first things a racer looks at is hematocrit levels. Hematocrit is one indicator of oxygen carrying capacity, so upon initial examination, this makes sense. Hematocrit probably became part of the consciousness of your average cyclist when the UCI created upper hematocrit limits before a racer has to take time off for “health reasons.” This somewhat arbitrary level of 50, and reports of some professional racers obtaining special certificates allowing them to have hematocrit over 50, has led many cyclists to expect that their hematocrit levels should be higher than that of a non-athletic person, and that higher is always better. But this is not necessarily true.
Your blood is mostly made up of red blood cells (RBC) and plasma; with platelets, white blood cells and other substances making up a very small percentage of your total blood volume. Hematocrit level is essentially the percentage of whole RBCs in your blood. When you train, the number of red blood cells goes up. But here’s the thing: plasma volume goes up even more than RBC volume. And since hematocrit levels are expressed as a percentage, hematocrit levels may actually go down. But this is ok, because you still have more plasma, and more RBCs than if you weren’t training. I sometimes explain it like this: if you are in an untrained state your hematocrit may be only 45, and as you train, it may go down to 42, but since it is 42 out of a larger total volume of blood, you actually have more RBCs in that trained state. To explain it another way, would you rather have 45% of $100 or 42% of $120? 42% of 120 is an extra $5.40, just like having extra hematocrit even though your levels have gone down from 45 to 42.
A hematocrit level of 42 is considered “normal” in most labs. But sometimes athlete’s hematocrit levels will drop lower, to levels that are flagged as “low” and the athlete can be told he has anemia, even when he does not. In some studies, the relationship between hematocrit and fitness is an inverse one, meaning that athletes with the lowest hematocrit were actually the fittest athletes in the study. Most athletes know that there is a relationship between iron and hematocrit. A simple explanation of that relationship is that iron is part of the “heme” portion of the red blood cells that actually carries the oxygen, and that appropriate levels of iron are required for your body to make adequate RBCs. This leads many athletes (especially those that have been told they are anemic) to consider supplementing with iron. There is no benefit to taking iron supplements when iron levels are already sufficient. Studies have shown that there is no athletic benefit to increasing iron stores in the blood once they are adequate. Iron is not easily excreted. The result is that over-supplementation can lead to iron toxicity and can even be deadly. This, along with the fact that low iron levels measured as serum ferritin can be as tough to diagnose as low hematocrit levels, means that I usually caution against athletes taking iron supplements.
Athletes do lose some iron through sweat, and female athletes lose some iron due to blood loss through the menstrual cycle, but in my opinion this iron is best replaced through a healthy diet rather than through supplementation. Animal products such as liver, beef, and lamb are the best sources of Iron, not only because they contain iron, but because iron from animal sources is more readily absorbed than iron from plant sources. Green leafy vegetables, beans, and tofu are good sources of iron, but those sources of iron are not absorbed as well as the animal sources. Vitamin C actually helps with the absorption, so tossing some oranges in your spinach salad can help with the iron absorption.
While I typically don’t recommend iron supplementation, it may be appropriate in some circumstances. That is a decision that should be discussed with your physician. But since hematocrit levels in athletes are frequently misunderstood among doctors as well as the general population, my recommendation is to see a doctor that is board certified in sports medicine, or at least a doctor that is accustomed to working with an athletic population.
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