Endurance exercise does not make people anemic, but it can deplete the body’s iron stores.
The causes and consequences of iron-deficiency anemia (IDA) generate a lot of interest and discussion in the fitness industry. After all, IDA can degrade exercise capacity and health status (Schumacher et al. 2002), and adult endurance runners may experience a reduction in iron stores (Kong, Gao & Chang 2014).
Iron (a mineral) is vital to life, but we do not need very much of it: As adults, we rarely have more than 3–4 grams in our bodies (NIH 2014). Most iron is in hemoglobin, the iron-rich protein that gives blood its red color; the remainder is stowed in the liver, spleen and bone marrow, and in myoglobin in muscle tissue.
Misconceptions about IDA, sports anemia and the role of iron in athletics are plentiful, and exercise professionals need to understand IDA before they can correctly educate their clients.
What Is Iron-Deficiency Anemia?
Iron-deficiency anemia happens when blood has a lower-than-normal red blood cell count. It can also occur if red blood cells (see Figure 1) do not contain enough hemoglobin. Hemoglobin is the transporter in red blood cells that delivers oxygen to all cells in the body.
People with IDA generally lack energy and feel tired, weak and sluggish (see Figure 2). Long-term IDA can impair function of the heart, brain and other organs (NIH 2014).
Although the terms iron deficiency and iron-deficiency anemia are often used interchangeably, it is helpful to see the distinctions:
- Iron deficiency is depletion of iron stores without health impairment.
- IDA is a critical clinical condition that degrades the functioning of several organ systems.
Iron plays a critical role in hemoglobin synthesis in red blood cells (see Figure 3), and insufficient iron stores become the starting point for developing IDA.
Hemoglobin tests can screen patients for iron deficiency. Hemoglobin concentrations lower than 13 g per deciliter in men and 12 g/dL in women indicate the possible presence of IDA (NIH 2014). This measurement has limits, however, because a low hemoglobin concentration may have other causes. That’s why hematocrit, ferritin and other blood tests are also common.
Hematocrit is the proportion, by volume, of red blood cells in the blood. Normal hematocrit levels are 36%–44% in females and 40%–50% in males (NIH 2014). For females, this means that the low percentage of the range (36%) represents 36 milliliters of red blood cells in 100 mL of blood, and the higher percentage of the range (44%) is 44 mL of red blood cells in 100 mL. Ferritin is the body’s major iron-storage protein, so a ferritin test will evaluate iron stores in the body to detect iron deficiency, iron overload and IDA.
What Causes Iron-Deficiency Anemia?
Common causes of IDA include loss of blood from bleeding, surgery or injury; and nutritional deficiencies in iron, vitamin B12 and folate (MedicineNet.com 2014). Cancer in the bone marrow and the suppression effects of chemotherapy drugs may lead to anemia. Kidney problems and destruction of red blood cells can also lead to anemia.
What Is Sports Anemia?
Sports anemia, also called exercise-induced anemia or pseudoanemia, should not be confused with IDA. Endurance exercise increases plasma blood volume proportionally to the exercise’s intensity (Kong, Gao & Chang 2014). Proportionally, plasma increases more than red blood cells do, so endurance exercisers may have low hematocrit levels.
Schumacher et al. (2002) explain that exercise stimulates an increase in red blood cells and a much larger increase in plasma volume. This explains why the term sports anemia is misleading: It’s not really anemia—it’s just an exercise-induced increase in plasma volume. Interestingly, this expansion of plasma volume reduces blood viscosity, making the blood thinner. That in turn may reduce resistance to the heart’s stroke volume, leading to more efficient cardiac output, enhanced delivery of blood to the working muscle, lower exercise heart rate and better dissipation of heat during exercise (Schumacher et al. 2002). Although these positive physiological adaptations indicate why the term sports anemia is deceiving, iron-deficiency concerns may exist for some endurance exercisers.
Importantly, Kong, Gao and Chang (2014) suggest that for some enthusiasts, intense endurance exercise may lead to chronic low-iron status, which may eventually impair athletic performance and health. These investigators note that the mechanism for the exercise-induced iron shortfall is yet to be fully explained in the research. Premenopausal female endurance clients may be at a higher risk for iron loss during menstruation.
It’s vital for endurance training clients to choose their diets carefully in order to sustain iron stores. Personal trainers should be aware that clients doing endurance exercise and restricting caloric intake to lose weight may be vulnerable to iron deficiency. Similarly, young athletes often become iron deficient because their diets don’t meet activity demands—these clients need to ensure they are getting enough iron from their food. Vegetarian athletes also need to pay special attention to dietary iron since they don’t get iron from animal sources.
Being able to distinguish between the realities of iron-deficiency anemia and the fallacies of sports anemia is most beneficial. Regular exercise does not cause anemia; rather, it improves many blood-related factors that enhance exercise capacity. However, recreational athletes and active clients need to monitor iron status as they increase energy expenditure and exercise intensity, and they should increase caloric intake to provide adequate foodstuffs and minerals (such as iron) for optimal physical function.