iron: micro minerals and the female athlete
The World Health Organization estimates that 10% of all women ages 15-59 in industrialized countries, 42% in non-industrialized, and almost 50% of all pregnant women share one thing in common: they suffer from anemia (World Health Organization 2016). Women are prone to iron deficiency and iron deficiency anemia (IDA) because generally they prefer different diets, eat less food, store lower amounts of iron, menstruate, and if they’re athletic, then excessive sweating, gastrointestinal bleeding, or increased plasma volume all can impact iron levels and affect fitness.
Iron forms 32.07% of Earth (Morgan and Anders 1980, 6975), but your body uses just three to four grams of iron for delivering oxygen to your tissues and muscles (Clydesdale 1985, 4), turning chemical energy from food into metabolic energy. Generally, the iron-built protein hemoglobin, part of your red blood cells, transports oxygen to your tissues. In muscles, the protein is myoglobin. Oxygen plays an important role in life, so your body recycles the iron from old red blood cells to prevent loss, and since this an efficient job, dieticians advise absorbing 2mg to 4mg each day depending on age, sex, pregnancy, frequency of donating blood, severity of menstruation, or existing medical conditions such as cancer (Eichner 2000, 327).
The value of dietary iron was known before modern medicine. The author William Shakespeare described the “green sickness,” now known as hypochromatic anemia, from poor iron intake and absorption in the play Pericles, Prince of Tyre.
Pandar: Now, the pox upon her green-sickness for me!
Bawd: ‘Faith, there’s no way to be rid on’t but by the way to the pox. Here Comes the Lord Lysimachus disguised.
In 1681 Thomas Sydenham infused wine with iron filings and prescribed the supplement to treat IDA (Eichner 2000, 326).
How does low iron affect me?
Your body can lose iron from blood loss, urine, sweat or parasites. Female populations in developing countries are at high risk for IDA because of diet, parasites like hookworms, and normal daily loss of iron.
There exist two stages before full IDA (Haymes 1987, 197), and it’s worth noting that symptoms aren’t always similar between two people with some mistaking how they feel as normal. Stage one begins when chronic (long-term) loss of iron stores (ferritin) results in reaching less than 15 micrograms/liter, known as “depletion (World Health Organization 2001).” Depletion of iron stores forces the body to produce new hemoglobin directly from absorbed iron. Iron absorption is logically related to your level of stored iron: if you have sufficient iron stores, then the body absorbs iron slowly. The contra-positive being if your iron stores are low or depleted, then your body increases the rate of iron absorption.
It’s important to note that endurance athletes, and even Olympic athletes, routinely test low-to-depleted iron stores without affecting their performance. Studies of distance runners and endurance athletes show risk for lower iron stores than comparable sedentary women. Iron levels in studied population of female runners were 28% lower than the control group (Pate et al. 1993, 227). Despite 50% of the runners being categorized as iron depleted, IDA was very low (Pate et al. 1993, 228). Samples of Olympic female endurance athletes found only 5% were IDA (Haymes 1987, 198). However this could be due to consistently eating a full diet with sufficient, fresh iron. But if your diet is lacking, then the body won’t produce new red blood cells as fast as needed because the hemoglobin building bricks are in short supply. Iron-deficient tissues are less able to carry out aerobic metabolism compared to tissues with sufficient iron stores. Studies of blood transfusion in rats showed that replacing anemic blood with proper hemoglobin did not affect endurance and work capacity in iron depleted rats, although VO2 max and hemoglobin levels returned to normal. Only after 8 consecutive days of iron treatment did endurance in iron depleted rats increase 50% with muscle lactate decreasing 50% (Haymes 1987, 199).
Stage two starts when you stay in stage one long enough without changing your diet, pushing the body into building red blood cells without enough hemoglobin. General symptoms of iron deficiency can show up as weakness, fatigue, irritability, poor concentration, headache, decreased exercise capacity, hair loss or dry mouth. In extreme or prolonged cases, a third stage will be reached. Symptoms here are more severe than stage two, and can manifest as feeling cold, inflamed tongue, shortness of breath during routine activities, and an appetite for non-nutritious things like chalk, ice or glass.
How can I maintain iron levels?
The recommended daily allowance (RDA) for adult (19-50), non-pregnant or breastfeeding, women is 18mg (U.S. National Library of Medicine 2016). Vegetarians and vegans will need twice this amount (National Institute of Health 2016). But digesting iron isn’t just eating a product that says “contains ‘x’% RDA of iron” because absorbing iron isn’t that straightforward.
Iron comes in two forms: iron that has already come from hemoglobin or myoglobin (heme iron), and iron that’s not from hemoglobin or myoglobin (nonheme). Heme iron comes from meats and poultry, and your body absorbs 15% to 35% (Spano 2015, 195) of what you eat. Nonheme iron is found in other foods such as vegetables, grains and fortified cereals, and your body absorbs 2% to 20% (Spano 2015, 195) of what you eat. The important difference of the two is absorbing heme iron isn’t influenced by what you eat, but if you eat certain foods or beverages with your meals, then you can influence how much nonheme iron you absorb. For example, tea and coffee contain compounds called “tannins” which bind with iron and make your intestines less efficient at absorbing iron. Spinach contains phytic acid that works the same way: binding to iron and creating a precipitate that’s hard to break down. Calcium and magnesium dense options have negative effects, but foods and drinks high in vitamin C positively increase your absorption of iron from nonheme. Eating heme-based food with nonheme-based foods increases the absorption of the nonheme iron. Bodyweight influences how much iron you absorb, too. In a 2015 study, overweight and obese women absorbed 2/3 of the iron relative to normal weight women, and iron-absorption enhancers (vitamin C) worked half as well (Cepeda-Lopez et al. 2015)
The best solution: maintain a diet filled with iron-rich foods such as lean red meats (beef), poultry, fish (salmon, tuna), iron-fortified grains, and other nonheme sources of iron like dried beans and dark green vegetables. If you eat more nonheme (e.g. vegetarian, vegan) sources of iron, increase your absorption efficiency by eating food or taking supplements high in vitamin C with your meals. If you feel taking actual iron supplements would benefit you, then talk to your doctor first because there exists negative side effects, harmful interaction with some medication, and healthcare risks from improper dosages.
Clydesdale, Fergus. 1985. Iron Fortification of Foods. Oxford: Elsevier Science. http://www.123library.org/book_details/?id=94549.
Eichner, E. Randy 2000. “Minerals: Iron.” In Nutrition in Sport, edited by Ronald J. Maughan, 326-338. Vermont: Blackwell Publishing.
Haymes, Emily M. 1987. “Nutritional concerns: need for iron.” Medicine and Science in Sports and Exercise 19 (5):197-200.
Cepeda-Lopez, Ana C., Melse-Boonstra, Alida, Zimmerman, Michael B., and Isabelle Herter-Aeberli. 2015. “In overweight and obese women, dietary iron absorption is reduced and the enhancement of iron absorption by ascorbic acid is one-half that in normal-weight women.” American Journal of Clinical Nutrition 102 (6):1389-97. doi:10.3945/ajcn.114.099218
Morgan, J. W., and E. Anders. 1980. "Chemical composition of Earth, Venus, and Mercury". Proceedings of the National Academy of Sciences. 77 (12):6973-6977. doi:10.1073/pnas.77.12.6973
National Institue of Health. 2016. “Iron. Dietary supplement fact sheet.” Last modified 11 February 2016. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
Pate, Russell R., Miller, Bonnie J., Davis, J. Mark, Slentz, Chris A., and Lisa A. Klingshirn. 1993. “Iron Status of Female Runners.” International Journal of Sport Nutrition 3:222-231.
Spano, Marie 2015. “Basic Nutrition Factors in Health.” In Essentials of Strength Training and Conditioning Fourth Edition, edited by G. Gregory Haff, N. Travis Triplett, 175-200. Illinois: Human Kinetics.
World Health Organization. 2001. “Iron Deficiency Anemia. Assessment, Prevention, and Control. A guide for programme managers.” Accessed 14 May 2016. http://www.who.int/nutrition/publications/en/ida_assessment_prevention_control.pdf
U.S. National Library of Medicine. 2016. “Iron in diet.” Last modified 2 February 2015. https://www.nlm.nih.gov/medlineplus/ency/article/002422.htm