|Understanding Iron-Deficiency Anemia & Sports Anemia
Amelia M. Weaver and Len Kravitz, Ph.D.
Much interest in the fitness industry surrounds some of the supposed causes and consequences of iron-deficiency anemia (IDA). IDA poses a negative influence on a person's exercise capacity and health status (Schumacher et al, 2002). As well, reduction of the body's iron stores may be seen in women and men endurance runners (Kong et al., 2014). Although vital to life, an adult only stores 3 to 4 grams of iron (NIH, 2014), mostly in hemoglobin, with the remainder stowed in the liver, spleen, bone marrow and myoglobin in muscle tissue. Several misconceptions about IDA and exercise exist. Having an understanding and an informative background on IDA is relevant for exercise professionals to correctly educate their clients.
What is Anemia?
According to the NIH (2014), anemia is a condition in which your blood has a lower than normal number of red blood cells. Anemia can also occur if your red blood cells don't contain enough hemoglobin, the iron-rich protein that gives blood its red color. Hemoglobin is the transporter on red blood cells that delivers the needed oxygen to all cells in the body. Individuals with IDA generally feel tired, weak, and sluggish and have a lack of energy. Long-term IDA can impair function of the heart, brain, and other organs in your body (NIH, 2014).
Although the terms 'iron deficiency' and 'iron deficiency anemia' are often used interchangeably, it is helpful to think of iron deficiency being a progression of depleted iron stores without health impairment, and IDA being a critical clinical condition that negatively affects the functioning of several organ systems. Iron plays a critical role in hemoglobin synthesis on the red blood cell and insufficient iron stores serve as the starting point for the development of IDA. Hemoglobin tests are commonly used measures to screen patients for iron deficiency. Hemoglobin concentrations lower than 13 g/dL in men and 12 g/dL in women indicate the possible presence of IDA (NIH, 2014). However, one of the problems with using this measurement in isolation is that low hemoglobin concentration is not caused exclusively by IDA, but may also be caused by various other factors, so hematocrit and ferritin measurements are commonly measured as well. Hematocrit is the proportion, by volume, of the blood that consists of red blood cells. Normal hematocrit values are approximately 36% to 44% in females and 41% to 50% in males and (NIH, 2014). So, for females this means that the low percentage of the range (36%) represents 36 milliliters of red blood cells in 100 milliliters of blood and the higher percentage of the range (44%) is 44 milliliters of red blood cells in 100 milliliters. Since ferritin is the body's major iron storage protein, its measurement is also a regular test used to evaluate iron stores in the body to detect iron deficiency, iron overload and IDA.
What Are The Causes of Anemia?
Some common causes of anemia include loss of blood from bleeding, surgery or injury as well as a nutritional deficiency in iron, vitamin B12 and folate (MedicineNet.com 2014). Cancer in bone marrow as well as the suppression effects chemotherapy drugs may lead to anemia. Kidney problems and red blood cell destruction can also lead to anemia.
What is Sports Anemia?
Sports anemia, also called exercise-induced anemia or pseudoanemia, has some unique differences with IDA. With endurance exercise there is an increase in plasma blood volume, that is proportional to the exercise intensity (Kong et al., 2014). Since this increase of plasma is greater proportionally then the increase in red blood cells, the hematocrit levels may be interpreted to be lower in the endurance exerciser. Shumacher et al. 2001 explain that exercise stimulates an increase in red blood cells, but this is outpaced by the superior increase in plasma volume. This explains why the term 'sports anemia' is misleading, as it is not true anemia, just exercise-induced increases in plasma volume. Interestingly, one advantage of having this proportionally greater plasma volume is there is lower blood viscosity (i.e., the blood is thinner), which may lead to a more efficient cardiac output (i.e., less resistance on heart's stroke volume), enhanced delivery of blood to the working muscle, lower exercise heart rate and better dissipation of heat during exercise (Schumacher et al, 2001).
Importantly, Kong and colleagues (2014) suggest that for some enthusiasts, intense endurance exercise may lead to chronic low-iron status, which will eventually impair an athlete's performance and health. They note that the mechanism for this exercise-induced iron deficiency is yet to be fully explained in the research. Pre-menopausal female endurance clients may be at a higher risk for iron loss during menstruation.
Dietary choices are important for the endurance training client to ensure she/he is sustaining the body's iron stores. Personal trainers should be aware that some clients who are doing endurance exercise and restricting their caloric intake, to attain weight management goals, may be vulnerable to iron deficiency, too. Young athletes often times can be iron deficient from an inadequate diet to meet their activity demands, and need to make sure they are eating foods that provide sufficient iron (see Side Bar 1). Alas, vegetarian athletes need to focus on iron status foods, since they are not getting iron from animal sources.
Side Bar 1. Frequently Asked Questions
1) What is Foot-Strike Hemolysis?
Hemolysis means the rupturing of red blood cells. Exercise-induced hemolysis has been shown in endurance runners, but not in endurance cyclists, suggesting that this red blood cell destruction is from the trauma of the repeated foot strikes in running (Schumacher et al., 2001).
2) Is it true that women who use oral contraceptives have higher iron stores?
Yes, a noticeable effect of women who take oral contraceptives is that since there is lighter blood loss due to menstruation, the body's iron stores are significantly higher than non-contraceptive users (Frassinelli-Gunderson, Margen and Brown, 1985).
3) What is the difference in heme and nonheme iron?
Dietary iron has two main forms: heme and nonheme (NIH, 2014). Heme iron is found in foods that containe hemoglobin such as meat, poultry, and fish. Plants and iron-fortified foods contain nonheme iron only. Heme iron is absorbed better than nonheme iron. Iron absorption is enhanced when both heme and nonheme iron are eaten together.
4) Are elderly persons more vulnerable to iron deficiency?
There is little direct evident of iron deficiency in elderly men and women.
5) Is iron deficiency more common in women?
Yes, particularly in women who are pregnant or breastfeeding or those who have recently given birth (ASH, 2014).
6) What are some animal sources of iron?
Fish--especially shellfish, sardines, and anchovies. Poultry--chicken, turkey, and duck, especially liver and dark meat. Meat--beef, pork, or lamb, especially organ meats such as liver (ASH, 2014).
7) What are some plant sources of iron?
Iron-enriched pastas, rice, grains, cereals, lima beans, peas, pinto beans, black-eyed peas, broccoli, kale, turnip greens, and collard greens (ASH, 2014).
Being able to distinguish and explain between the realities of iron-deficiency anemia and the fallacies of sports anemia is most beneficial. In actuality, regular exercise does not cause anemia, rather it improves many blood-related factors that positively affect exercise capacity. Athletes and active clients should be aware of their iron status and of their increased levels of energy expenditure, which dictates the need for increased caloric intake to provide both adequate foodstuffs and minerals (such as iron) for optimal physical function.
Amelia M. Weaver an Exercise Science major with a minor in Spanish at the University of New Mexico (Albuquerque). Her research interests include anatomical and pathological abnormalities, particularly those pertaining to muscular and nutritional imbalances. She is starting coursework at the US Army-Baylor University Doctoral Program in Physical Therapy.
Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. He has received the prestigious Can-Fit-Pro Lifetime Achievement Award and American Council on Exercise Fitness Educator of the Year.
ASH, American Society of Hematology. Iron Deficient Anemia (2014).
Accessed May 22, 2014
Beard, J.L. (2001). Iron biology in immune function, muscle metabolism and neuronal functioning. Journal of Nutrition, 131, 568S-580S.
Frassinelli-Gunderson, E.P., Margen, S., and Brown, J.R. (1985). Iron stores in users of oral contraceptive agents. American Journal of Clinical Nutrition, 41(4), 703-712.
Kong, W-N, Guofen, G. and Chang, Y-Z. (2014). Hepcidin and sports anemia. Cell & Bioscience, 4: 19.
MedicineNet.com. (2014). Hematocrit
Accessed May 21, 2014
NIH, National Institutes of Health: Office of Dietary Supplements (2014). Iron, Dietary Fact Sheet
Accessed May 21, 2014
Schumacher Y.O., Schmid, A., Grathwohl, D., Bültermann D., and Berg, A. (2002). Hematological indices and iron status in athletes of various sports and performances. Medicine & Science in Sports & Exercise, 34(5), 869-875.