There are several forms of anemia. The type we are concerned with is iron-deficiency anemia. Why? Because this is the type of anemia that most often affects athletes.
Iron-deficiency anemia is defined as a decrease in the number of red blood cells and or lower than usual amounts of hemoglobin. (Hemoglobin is the protein that carries oxygen molecules in the blood.) This is typically a direct result of insufficient amounts of iron, whether it is from inadequate dietary intake or accelerated loss from the body.
Symptoms of anemia include dizziness, fatigue, shortness of breath, rapid heartbeat, cramping, insomnia and other symptoms. Many times, an athlete will just feel out of breath and have no ‘get up and go’. It goes without saying that anemia is detrimental to an athlete’s performance. Newer research also shows that anemia can inhibit gains in performance as a result of training.
What’s Diet Got To Do With It?
You’ve probably already heard that vegetarians/vegans are at highest risk. Why? Well, animal products, specifically red meat have the highest amount, and most easily absorbable form of iron. Plant foods do contain iron, however in smaller amounts and in a form that is less bioavailable - meaning it is more difficult to absorb. Also, high fiber foods like bran can inhibit iron uptake. Plant chemicals (phytates found in green leafy foods, tannins in coffee, tea and wine) are also notorious for inhibiting iron uptake.
Who is At Risk?
Typically, women of reproductive age are considered at highest risk due to blood loss (through menstruation). We just mentioned vegetarians and vegans. A third high-risk group includes the people reading this article, endurance athletes. Athletes lose iron through sweat, bleeding in the gut, and something known as exercise-induced hemolysis, or the destruction of red blood cells during the course of exercise. These are all 'normal' avenues of iron loss - especially in runners.
Avenues of Iron Loss in Athletes
Sweat-related Iron Loss
Iron loss will occur to an extent through sweat, whether the amount lost is clinically significant continues to be argued. A handful of studies have attempted to define the amount of iron lost through sweat (this is quite difficult to achieve in order to mimic ‘real life’ conditions). One such study estimated that sweat losses average only 22 micrograms per liter of sweat. (1) Another study suggests total daily iron loss is closer to 1 milligram. Regardless, this is not a large amount of iron, but it is another avenue through which athletes can potentially lose iron.
GI-associated Iron Loss
More specific to distance running as well, gastrointestinal bleeding is a common occurrence (2, 3) and is thought to be a contributory factor for exercise-induced anemia. It is thought that with greater intensity and duration, more blood is lost in the GI tract.
There are a handful of theoretical reasons for GI-related blood loss. Physical activity leads to a decreased supply of blood to the abdominal organs as blood is shunted to working muscles for fuel and to the skin for heat dissipation. This relative lack of blood supply to the abdomen can lead to tissue erosions or inflammation, such as ischemic colitis or gastritis, both of which are known causes of bleeding in athletes. (4) Otherwise, repetitive motion of the organs ‘rubbing’ against each other from continued pounding on hard surfaces may also cause bleeding.
Lastly, one of the most significant causes of GI bleeding in athletes are non-steroidal anti-inflammatory drugs, or NSAIDS. While not directly related to exercise, this bleeding will occur in any person taking them. Athletes are quite likely to use these medications for training related aches and pains.
NSAIDs have other side effects that all athletes should be aware of.
Urinary Iron Loss
Some runners report blood in the urine after distance running. This can be caused by decreased blood flow to the kidneys or damage to the bladder from the continuous pounding of running. Anytime there is blood in the urine, this could signify a serious medical condition and you should get it checked out.
Exercise Induced Hemolysis
As blood cells pass through the feet of runners, they can become damaged and destroyed. This is termed ‘exercise induced hemolysis’ and researchers speculate several different causes of this. It's thought that as red blood cells pass through the feet of runners, the repetitive force from striking the feet on the ground destroys the red blood cells. (5) However, exercise-induced hemolysis has been reported as a result of other activities including rowing, weight lifting and swimming. (6,7,8) Despite these other exercise-related causes; runners exhibit far more red blood cell destruction compared to these other groups. Interestingly, studies have shown that while runner’s RBC destruction is greater (roughly 4 times) than other athletes, overall RBC counts between athletic groups (i.e. runners compared to cyclists, etc) show no significant difference. However, runners are still at greater risk of developing anemia, especially those in which training volume increases to a point where RBC synthesis mechanisms may become overwhelmed (twice daily workouts, marathoners, etc).
Diagnosis can in some ways be complex. Newer tests for anemia may further complicate obtaining a proper diagnosis.
At The Natural Athlete, we are not fans of the typical way that iron-deficiency anemia is diagnosed. Standard medical evaluation tends to favor ‘reactive’ iron prescribing, or not until the athlete prominently displays fatigue, low hemoglobin and ferritin – iron deficiency anemia. Frankly, these are late-stage signs of iron deficiency anemia, which may take several months to occur after an extended period of iron deficiency. This method leaves the athlete with a gap in their training schedule as the descent into, and the climb back out of the iron-deficiency hole can take several months. (And newer studies point to the fact that symptoms and side effects of anemia can manifest well before a person shows laboratory signs, such as low hematocrit or hemoglobin). Rather, we choose to closely monitor serum ferritin as it mirrors total body iron content and supplement iron based on these levels.
So which tests should you ask for? For starters, we recommend having your hematocrit (number of red blood cells), hemoglobin (oxygen-carrying protein) and ferritin (a storage form of iron) looked at every 4 months to monitor for anemia, especially if you are female, vegetarian/vegan, have a history of anemia, or otherwise at risk for iron-deficiency anemia. (There are other forms of anemia that are more rare and we therefore do not recommend regular screening for them). Vegetarian/vegans should also monitor blood levels of vitamin B-12 and folate; this can cause another type of anemia that we haven’t talked about.
If you are concerned about anemia, other tests to order include:
• Serum Ferritin
• Total Iron Binding Capacity (TIBC)
• Percent Transferrin Saturation
Supplementation with iron is often necessary to maintain iron levels that tend to drop rapidly, and of course for low levels. Do not supplement with iron unless you have undergone appropriate testing and consult a medical professional. You should never self-treat with iron; it can be quite easy to overdose on and this will cause serious health problems. Iron is deadly for small children. In fact it is the leading cause of death from accidental overdose in small children..they like to munch those vitamins that contain iron! Keep all supplements far away from kids, just like you would other medications.
The first step in preventing and treating iron-deficiency anemia is to examine the diet for adequate iron sources. Some of the richest sources of iron in foods are animal products such as oysters, clams, liver, beef, sardines, and turkey, to name a few. Iron found in animal flesh is referred to as heme iron and is easily absorbed. Iron found in plants such as beans, lentils, nuts, seeds, and dark green leafy vegetables contain non-heme iron that is not as readily absorbed.
Drinks to avoid when eating iron-rich foods include tea and coffee due to their tannic acid content (which binds iron and prevents it from absorbing). Dairy products contain phosphates that slow absorbtion, spinach contains oxalic acid, and beans contain phytates, both of which inhibit iron absorbtion. If you are supplementing with iron, it doesn’t mean you cannot ever eat these foods, only consume them in moderation and away from your iron supplement.
To enhance absorbtion of iron, take it with vitamin C. You only need to take about 1000 milligrams of vitamin C with your iron pill.
1. Brune M, Magnusson B, Persson H, Hallberg L. Iron Loss in Sweat. The American Journal of Clinical Nutrition 43: March 1986, pp 438-443.
2. Baska RS, Moses FM, Graeber G, Kearney G. Gastrointestinal bleeding during an ultramarathon. Dig Dis Sci. 1990 Feb;35(2):276-9.
3. Halvorsen FA, Lyng J, Ritland S. Gastrointestinal bleeding in marathon runners. Scand J Gastroenterol. 1986 May;21(4):493-7.
4. Schwartz AE, Vanagunas A, Kamel PI: Endoscopy to evaluate gastrointestinal bleeding in marathon runners. Ann Int Med 1990; 113: 632-633.
5. Telford RD, Sly GJ, Hahn AG. Footstrike is the major cause of hemolysis during running. J Appl Physiology 94: 38-42, 2003.
6. Eichner ER. Gastrointestinal bleeding in athletes. Phys Sports med 17: 128-140, 1989.
7. Schobersberger W, Tschann M, Hasibeder W. Consequences of 6 weeks strength training on red cell O2 transport and iron status. Eur J Appl Physiol 60: 163-168, 1990.
8. Selby GB, Eichner ER. Endurance swimming, intravascular hemolysis, anemia and iron depletion. New perspective on athletics anemia. Am J med 81: 791-794, 1986.
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