Classification and usage
Iron is an essential trace mineral that is required by each body cell. The healthy levels of iron in the blood are between 20 and 25 µg/Dl. This nutrient is involved in the transportation of oxygen in the vascular system and muscles. Also, it is an important constituent of the electron transport system that is involved in the regulation of energy release from the cells. Iron is imperative in the production of red blood cells and it is an element of a healthy immune system. Hence, in the case of endurance athletes, iron status is an important requirement, which if compromised will lead to poor athletic performance. The body’s needs of iron should be met by the food consumed. Iron is available in food in two forms: heme and non-heme iron. Heme iron from meat sources has the best absorption rate (15-18%) while the converse is the case for non-heme iron whose absorption rate is <5%. Non-heme iron is obtained from plant sources.
Iron supplementation comes in two forms: oral supplementation and intramuscular iron injection. Iron supplementation prevails, either as ferrous or ferric iron, and ferrous iron is more bioavailable. Clinically used oral supplements are in the form of ferrous sulfate, ferrous fumarate, or (hydrated) ferrous gluconate. Oral iron supplementation takes around 6 to 8 weeks for it to improve the iron status of an athlete. However, if a faster remedial action is required, intramuscular iron injection is the ideal option. Unfortunately, no evidence supports the use of iron supplementation to enhance endurance performance. In the same way that women have a higher risk of iron deficiency in the general population is the same way the female athletes are more susceptible to iron loss and negative iron balance. Based on older studies that still hold water, more current studies tend to focus on iron loss among female athletes. Female athletes have greater iron needs than their male counterparts; whereas the recommended intake for females between 19-50 years is 18mg/day, the recommended intake for their male counterparts between 19 and 70 years is 8mg/ day. The upper limit is 45 mg/day, beyond which iron is presumed to have damaging toxic effects. Unfortunately, as stated by Knigge (2014), most women only consume 12-15mg/d of iron in comparison to the recommended allowance of 18mg/d for premenopausal women.
Despite the fact that the diet is a great cause for negative iron balance, hematuria also results in this negative balance. Endurance runners are most affected as a result of foot impact. In addition, endurance athletes experience sweat losses, myoglobin leakage, heavy menstrual losses, and gastrointestinal losses, all of which lead to iron loss; hence, the need for supplementation. Despite the fact that some studies indicate no benefit of iron supplementation, it is inarguable that iron loss requires supplementation. 100mg of ferrous sulphate is believed to increase the levels of serum ferritin (SF) by 30-50% in 6 to 8 weeks. The absorption of iron supplements is enhanced by simultaneously ingesting ascorbic acid derived from fruits and fruit juices. The converse happens when iron supplements are ingested in combination with caffeinated products, antacids, and some minerals as mentioned below. Hence, it is imperative to use an iron supplement that equally contains vitamin C, such as Ferro-gradumet C as advocated by (Goodman et al., 2011). Iron supplements that are prepared alongside other minerals, especially calcium, zinc, and manganese salts have a low bioavailability of iron.
Iron is fundamental in the delivery and utilization of oxygen because it is the functional component of both myoglobin and hemoglobin. In addition, it is essential in promoting oxidative phosphorylation because it is a critical component of mitochondrial enzymes and cytochromes (Goodman et al., 2011). It is claimed that iron insufficiency leads to lethargy and decreased athletic performance. Iron supplementation among athletes should be monitored every 8 to 12 weeks through a blood test since iron toxicity might result. The dosage of iron supplement given depends on one’s iron status that ranges from iron depletion to iron deficiency. Hence, it can be as low as 10mg to 325mg.
Performance Claims
Unfortunately, much debate revolves around the benefits accrued from iron supplementation even though the sporting community has been involved in investigative research on supplementation for more than 20 years. Whereas some studies indicate no effect on performance, others indicate the converse. This variation is justified based on the approach used by the researchers to defend their rationale and research objectives/questions. In addition, athletes have misguided perceptions about the use and benefits of iron supplements. Despite having a healthy iron status, athletes, and mainly men, tend to take iron supplements, regardless. Hence, it is no wonder that iron overload has been more prevalent among men. However, iron supplementation enhances performance among athletes with decreased iron stores or who are iron-deficient. Williams (2005) notes that iron supplementation will only benefit endurance athletes if their objective is to increase their red blood cells. However, enhanced performance will not be achieved since supplementation aims to prevent the dysfunction attributed to iron loss and iron deficiency. Indicators used to assess a person’s iron deficiency include transferrin saturation, serum iron, serum ferritin, hemoglobin, hematocrit, and total iron binding capacity.
A pre-post study by DellaValle and Haas (2011) helps to understand performance claims by studying the iron status of female collegiate rowers and how it relates to rowing performance. In this study, there was a significant association between the levels of serum ferritin and 2-km performance times; poor iron status led to the rowers’ 2-km time. Poor iron status results in the genesis of few iron-dependent enzymes. Subsequently, the main energy pathway used by rowers to transform chemical energy to mechanical energy is impaired during endurance training. Thus, the rowers were not able to achieve optimal performance unlike in the situation when they would have had recommended levels of iron status. In addition, due to poor iron status, usually, there is impaired oxygen transport capacity, notwithstanding the presence of anemia, which leads to a reliance on anaerobic metabolism in the production of energy. Unfortunately, this survey did not measure oxygen consumption or blood lactate as these would have provided more evidence on the essence of iron supplementation due to a noted deficiency. Future studies need to focus on such elements while keeping note of confounding factors, such as fat-free mass and VO2peak.
Pasricha, Low, Thompson, Farrell, & De-Regil (2014) are among those researchers that support iron supplementation for athletes. According to their review, iron supplementation was deemed to have positive effects on maximal and submaximal exercise performance. In addition, iron supplementation reduced heart rate, enabling athletes to increase their endurance levels. The same effects had been earlier reported by Hinton and Sinclair (2007), who showed that iron supplementation led to increased gross energetic efficiency. The first response of iron supplementation is increased serum ferritin; however, this has not been shown to influence hemoglobin or hematocrit.
Effective Claims
The study by Hinton and Sinclair (2007), “Iron supplementation maintain ventilator threshold and improves energetic efficiency in iron-deficient nonanemic athletes” published online on 12th July 2006 in the European Journal of Clinical Nutrition aimed to determine the effect of iron supplementation on iron status and endurance capacity. The study adopted a randomized, double-blinded approach and 20 subjects voluntarily were fully involved to the end. 30mg of elemental iron in the form of ferrous sulfate versus a placebo were administered daily over a period of 6 weeks. Dietary intake and level of physical activity between the placebo and experimental groups were not different. There was a significant increase in serum ferritin in the experimental group in comparison to the placebo group. However, Hb or hematocrit levels remained unaltered. There was a decline in ventilator threshold in the experimental group compared with the placebo group, and greater effect was seen among individuals with the lowest levels of serum ferritin before administration of the intervention. Whereas supplementation had a positive impact on gross energetic efficiency due to concurrent increases in serum ferritin, the converse correlation was seen between serum ferritin and average respiratory exchange ratio. Despite the fact that this study indicated that iron supplementation was effective in improving iron status and endurance capacity among iron-deficient nonanemic athletes, future researches ought to include a larger sample size.
A 2014 systematic review, “Impact of oral iron therapy on exercise performance in adult iron depleted female athletes” by Nicole Knigge based on a capstone project at the school of Physician Assistant Studies in Pacific University aimed to determine the effect of iron repletion on the endurance performance of female athletes diagnosed with iron deficiency but are not anemic. The review involved MEDLINE-PubMed, Web of Science, CINAHL, and MEDLINE-Ovid databases using ‘dietary supplements’ ‘iron,’ and ‘sports’ as keywords. The articles had explicit inclusion and exclusion criteria of the articles included, but the most relevant criteria was the fact that all the included studies were double blinded and controlled without crossover. In addition, the quality of these research articles was determined using GRADE criteria; hence, the quality of the systematic review is guaranteed. Only two studies met the criteria. These articles indicated that iron supplementation is involved in the increment of iron stores, but not the endurance capacity. However, the studies reviewed had a sample consisting of a heterogeneous group of athletes and were implemented for short duration: 8 weeks.
Safety and Health Risks
Literature indicates that endurance athletes are at risk of iron loss; hence, it is safe for them to take a multivitamin with iron whose bioavailability is enhanced and not thwarted by minerals such as calcium. Otherwise, the efficacy of such a supplement in correcting iron depletion is not assured. Beard and Tobin (2000) report that consumption of >50mg Fe/day is associated with noncompliance issues. In addition, frequent complaints of constipation due to hemochromatosis, nausea, vomiting, dark colored stools, diarrhea, and gastrointestinal distress have been linked to intake of high-doses of iron supplements and could be the main reason for noncompliance. Lower doses of iron supplementation, for example, 39mg Fe/day (≤125mg ferrous sulfate) prevents a decrease in serum ferritin and are not associated with gastrointestinal discomfort. In addition, dividing the dosage into two or three times a day, taking it with food and titration of the supplement to recommended levels helps to minimize the side effects and associated severity.
How athletes supplement themselves with iron based on the rationale that it will enhance their performance is not safe for their health. Consumption of iron supplements without monitoring might result in toxicity that is pro-oxidative and is associated with various chronic diseases. Unfortunately, few studies have focused on iron overload in relation to performance. The current scientific literature does not support iron overload. According to Mettler and Zimmermann (2010), iron overload results in reactions between iron and unsaturated fatty acids to generate free radicals that are a reason for most chronic diseases, including cancer. In addition, high iron stores lead to oxidative stress and damage of the DNA. A level increases one’s susceptibility to myocardial infarction. Individuals who have a genetic predisposition to hemochromatosis are at risk of organ damage due to iron overload, but more conclusive results on this genetically predisposed group are necessary to clear the prevailing contraindications.
Ethical/Legal Considerations
Iron supplements are approved for use, and there is no ban on them from any sports governing agency. Nonetheless, upon detection of iron depletion and/or iron deficiency, one should consume iron supplements under the guidance and supervision of a nutrition consultant so that necessary dietary adjustments can be made, equally (Jenkinson & Harbert, 2008). Self-prescription of iron supplements when one is not deficient might result in toxicity that is as harmful as iron deficiency. Hence, athletes should take up screening blood tests to determine their iron levels, and subsequently seek health advice on the level of supplementation they should adopt. Intravenous iron infusions are a much faster method of correcting iron deficiency, but unlike intramuscular injections of iron, intravenous iron transfusions are banned by the World Anti-Doping Agency (WADA) and Australian Sports Anti-Doping Authority (Goodman et al., 2011).
Summary/Recommendations
Iron supplementation is important for endurance athletes because they tend to lose more iron compared to other types of athletes and the general population. Iron supplementation is recommended when serum ferritin levels are low, with or without anemia. Hence, iron supplementation should not be used as an ergogenic aid because it is not aimed at boosting performance. Rather, it helps to correct iron depletion and/or iron deficiency. The use of low iron supplementation has equivocal benefits as high-dose iron supplementation and does not bring about gastrointestinal distress. Due to the different levels of iron deficiency, endurance athletes must obtain valid information on the ways to correct a deficiency because Jenkinson and Harbert (2008) note that a decrease in serum ferritin without anemia can be corrected easily using dietary changes. The use of iron supplements should not be based on the subjective judgment that one is predisposed to anemia; rather, a hematological evaluation should guide one’s use of iron supplements.
References
Beard, J., & Tobin, B. (2000). Iron status and exercise. The American Journal of Clinical Nutrition, 72(2), 594s-597s.
Goodman, C., Peeling, P., Ranchordas, M. K., Burker. L. M., Stear. S. J., & Castell, L. M. (2011). A to Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance-Part 21. Br J Sports Med, 45, 677-679.
Hinton, P.S., & Sinclair, L.M. (2007). Iron supplementation maintains ventilatory threshold and improves energetic efficiency in iron-deficient nonanemic athletes. European Journal of Clinical Nutrition, 61, 30-39. Web.
Jenkinson, D. M., & Harbert, A. J. (2008). Supplements and sports. American Family Physician, 78(9), 1039-1046.
Knigge, N. (2014). Impact of Oral Iron Therapy on Exercise Performance in Adult Iron Depleted Female Athletes. School of Physician Assistant Studies. Paper 491. Web.
Pasricha, S., Low, M., Thompson, J., Farrell, A., & De-Regil, L. (2014). Iron Supplementation Benefits Physical Performance in Women of Reproductive Age: A Systematic Review and Meta-Analysis. The Journal of Nutrition, 144(6), 906- 914. Web.
Williams, M. H. (2005). Dietary supplements and sports performance: Minerals. Journal of the International Society of Sports Nutrition, 2, 43-49.