You've been training hard for an upcoming race, but recently you've struggled to complete workouts. You are getting more sleep but feel tired. Should you have your iron levels checked? Iron is important, but not all that you hear is true. Here are some common questions:
How does low iron affect running?
Iron, a trace element in the body, is involved in the function of the immune system and energy production system, but its most critical role is in getting oxygen to your muscles. Iron is a major component of hemoglobin, the transport agent for oxygen and carbon dioxide in the blood. It is also present in muscles in the form of myoglobin, the protein that extracts oxygen from hemoglobin molecules. For metabolism and transport of oxygen to function properly, an adequate level of iron must be available. This is especially true during growth and physical activity.
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As a general rule, exercise does not predispose an athlete to anemia, but the symptoms associated with anemia--most commonly excessive fatigue--may become apparent earlier in an athlete. Anemia indicates a deficiency of red blood cells (RBC) in the body. There are many causes, with iron deficiency being the most common. Anemia may be due to excessive loss and/or inadequate production of RBC.
Is anemia common among runners?
The prevalence of anemia in U.S. men under the age of 45 years is 0.2 to 0.6 percent. Due to a variety of medical conditions, this increases to 1.8 percent in men age 75 years and older. The prevalence in women is approximately 3 percent. Iron deficiency anemia is more common in women of childbearing age, due to menstrual loss, especially in conjunction with inadequate intake of iron in the diet. Vegetarians are at increased risk of anemia if they are not careful about dietary intake.
There is not an increased prevalence of anemia in athletes, but mild anemia that may go unnoticed in the general population can impact athletic performance.
While anemia may not be more common in athletes, studies have found that ferritin levels may be lower in female athletes and in male endurance athletes than in their non-athletic counterparts. If iron stores are low and there is greater loss of RBCs than production, this may progress to anemia. If iron stores are lower than 20ng/ml (some will even recommend 30ng/ml), iron supplementation would be recommended.
One effect of regular endurance exercise is that it produces an increase in red blood cell mass and plasma volume. This results in the greater delivery of oxygen to exercising muscles and more effective removal of carbon dioxide. The increase in plasma volume due to exercise is greater than the increase in RBC mass, resulting in a slightly lower hemoglobin level in runners than in nonathletes.
This dilution is known as athletic pseudoanemia and is not a true anemia. If a runner is tested low but not experiencing symptoms, no change is necessary. Those experiencing unexplained fatigue or decrease in performance should take a few days off from training. If anemia was the source of symptoms, the hematocrit and hemoglobin would not improve; if results were due to dilution, the numbers would normalize, indicating that anemia was not causing the problems.
How much iron do I need? Do I need more as a runner?
Iron is stored as ferritin in the liver, spleen and bone marrow. Ferritin levels measure these iron stores in the body; levels less than 12ng/ml correlate with a lack of bone marrow iron stores. The level of ferritin has a tremendous impact on the absorption of iron from the diet. Absorption is enhanced when stores are low. The actual level that is considered low varies in different studies. Low levels of ferritin don't necessarily mean that somebody is anemic.
There is disagreement as to whether low ferritin levels affect athletic performance. In several studies, low levels did not have an effect on VO2 max. Other studies demonstrated improvement in performance after athletes who had low ferritin levels, but not anemia, supplemented their iron intake. This may be due to a relative anemia (hemoglobin is in the normal range, but is low for the particular athlete) and not just a low ferritin level.
The athletes (all female) who experienced improvement in performance had hemoglobin levels at the lowest end of the normal range; they experienced an increase in hemoglobin level in addition to improvement in performance. Other athletes with similar initial blood tests did not experience a change in hemoglobin level after taking iron supplements. The take-home message: If your hemoglobin or hematocrit (percentage of RBC) level is at the low end of the normal range, a trial of iron supplementation may produce an increase in these levels and a related performance improvement.
Does the pounding of running cause red blood cell loss or iron loss?
There is a phenomenon known as foot-strike hemolysis (more appropriately named exertional hemolysis) in which red blood cells are destroyed during exercise. This was initially thought to be due to compression of capillaries in the feet while marching and running, but additional factors must come into play, as this process has also been noted in swimmers, rowers and weightlifters. The blood cell loss typically is not significant enough to be detected on a routine blood test.
We all lose iron every day. Small amounts are lost through the gastrointestinal tract, and trace amounts are lost in sweat and possibly in urine.
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The recommended daily intake for elemental iron varies depending on gender and age, ranging from 8mg/day to 18mg/day (27mg/day during pregnancy). The higher range of intake may be difficult to maintain, especially for vegetarians, who need to take in more iron because less is absorbed from nonmeat sources. Heme iron, found in red meat and dark poultry, is a more readily available source of iron (18 percent absorbed). Our bodies absorb about 10 percent of non-heme iron from vegetables and grains. Vitamin C, taken in conjunction with a meal, improves the absorption of non-heme iron, as does meat protein. Tannins (found in tea) and calcium can decrease absorption.
Should I supplement iron?
Iron alone does not increase the production of RBCs; this is a complex process involving multiple factors impacting the bone marrow. When cells are depleted of iron, supplementation will increase the hematocrit and hemoglobin. If levels are not low, excess iron will not produce additional RBCs, nor provide a performance boost.
Iron supplementation in a low dose is not harmful for most people, but it is possible to develop an iron overload. Approximately 1 person in 250 of Northern European descent carries the gene for hemochromatosis, a disorder in which iron is absorbed too efficiently and excess amounts are deposited in the organs of the body. Only about 10 percent of those with the abnormal gene develop significant organ damage. Hemochromatosis is commonly not diagnosed until damage to organs has occurred (heart failure, cirrhosis). Iron supplementation, even the amount in a multivitamin, may accelerate the effects of this disorder. Supplements may also mask underlying medical conditions, such as celiac disease and occult blood loss from the GI tract, which will delay the diagnosis and appropriate treatment of these disorders.
The impact of iron supplementation on the performance of athletes with low ferritin levels without anemia is still unclear. Research continues on this subject, and at some point, the data may provide more definitive answers. Because of the importance of iron in the body, supplementing low levels of ferritin to avoid depletion of iron stores is recommended.
The amount of iron in a multivitamin can supplement dietary intake and is safe in the absence of an iron storage disease, such as hemochromatosis. This small amount will not cause a change in the complete blood count (CBC) or ferritin level. Greater doses are required to impact the ferritin level. You should discuss the appropriate dose of iron supplementation with your health care provider. As the dose of the supplement increases, so does the likelihood of gastrointestinal side effects, including constipation, nausea, vomiting and abdominal discomfort.
How does low iron affect running?
If you are healthy and your training is going well, you do not need to be screened for anemia or low iron stores. Although it would be nice to see the results, your insurance company may not pay for blood tests for asymptomatic screening. Women with heavy menstrual bleeding and vegetarians are at greater risk of low iron stores and anemia, and screening may be justified. If you have a history of a medical problem that could cause anemia (such as an ulcer or celiac disease), blood tests may be warranted.
If you are experiencing unexplained fatigue and/or a decrement in performance that has persisted for several weeks, a CBC and ferritin level are good initial screening tests for anemia. If anemia is not detected and iron stores are low, you may work on enhancing your diet and/or take an iron supplement. (Discuss this with your health care provider to ensure that there is not a contraindication.) If anemia is detected, it's important to determine the cause of this problem in addition to beginning iron supplementation. You should avoid iron supplementation if you have a family history of hemochromatosis. Your health care provider should test you for this disorder.
