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Athletes are often encouraged to learn the science behind their training. Why they should eat carbs or protein, why they need so much sleep and why the ferritin level of their blood should never get too low. Information sheets about all of these topics are often distributed to young endurance athletes by their coaches and, by the time they reach adulthood, they might think they already know everything they need to.
Aerobic exercise with low iron levels in the blood is painful. Oxygen can’t get to your body fast enough and no matter how many great, gasping gulps of air you take, you can’t keep up. Once you learn that it might be low iron, everyone tells you that it’s normal. This often happens to runners, especially runners who menstruate. Runners who menstruate also tend to have lower concentrations of hemoglobin — an essential protein for transporting oxygen throughout the body.
So why does this happen? What happens when we engage in aerobic exercise? A 1985 study measured changes in formed elements of the blood (cellular elements within the plasma: red blood cells, white blood cells and platelets — Over 99 percent of the formed elements are red blood cells) in female high school cross country runners, looking at the hematocrit (the number of formed cells in your blood), hemoglobin concentration, white blood cell count and red blood cell count. Measurements were taken twice at the beginning, middle and end of the season both before exercise and soon after. The study found a slight decrease in hematocrit, an increase in hemoglobin concentration over the course of the season, slight increases in white blood cell count and, notably, major red blood cell count increases.
An important role of red blood cells is to carry oxygen throughout the body, and aerobic exercise requires this function to be done quickly and often. Aerobic athletes often have an abundance of red blood cells because their bodies feel the demand of constant exercise, and build more red blood cells in order to maintain the level of activity. This is why training at altitude is popular with endurance athletes; the lack of oxygen in the air naturally stimulates more red blood cell development. This increase, no matter how it is achieved, is what long-distance runners refer to as endurance: it’s just more working red blood cells. The key word there is “working.” Hemoglobin must be bound to iron in order to attach to oxygen, and if this reaction does not occur, oxygen can not be picked up from the lungs as we breathe and then circulated throughout the body. It is important to note that endurance athletes may have a red blood cell count that falls within the “normal” range, but their activity level is still too difficult to maintain because they struggle to circulate oxygen effectively, as the red blood cells are rendered useless without iron bound to hemoglobin.
Iron is most often absorbed into the body through the digestive tract. Digestive difficulties, such as those that a person with celiac disease faces, naturally make iron more difficult to obtain. This means that while most people get this nutrient through food, many also choose to take capsule iron supplements. Heme iron, which comes from animal products that contain hemoglobin, is the easiest to absorb. Nonheme iron, though more difficult for the body to absorb, is still able to yield the nutrient, and is found in the majority of iron-containing foods (so, do not worry, vegetarians and vegans whose parents disapproved on the grounds of “how will you get your iron!”). Symptoms of anemia, besides diminished athletic performance, are feeling cold, feeling tired and for some, having the appearance of pale skin.
For many endurance athletes of any gender, iron deficiency becomes an issue at some point. Though not the focus of this article, it is also quite common among people who do not engage in regular aerobic exercise. If you are concerned about your iron intake, Lowry’s clean bean is always a great start!