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Iron: An Essential Mineral for Endurance Athletes

best electrolytes for runners

Iron is a trace mineral that is essential, not just for peak athletic performance, but for life. Iron minerals in our food are the same as you would find in metal or on the periodic table of the elements. Of the minerals related to athletic performance, iron is easily one of the most important, and it is easy to see why when considering all of irons functions. Let's take a look!

What Does Iron Do In The Body?

best electrolyte tab for runners

Iron has 3 primary functions. Approximately 5% of iron can be found as a functional or structural component in some proteins, like collagen, enzymes, neurotransmitters, and white blood cells for immunity. Having a poor iron status can negatively impact any of these areas resulting in weaker bones, increased rates of sickness, and poor mood.

Second, about 25% of iron is in ferritin. Ferritin is a protein with the function of storing iron and preventing iron toxicity. Similarly, ferritin can convert iron from having a +2 charge to a +3 charge. This may seem trivial, but it actually is crucial, as iron with a +3 charge can produce free radicals. Most often, ferritin is used to measure iron status.

Lastly and most importantly, 70% of iron is used to form the oxygen-transporting proteins hemoglobin and myoglobin. Hemo – blood. Myo – muscle. Globin – protein. Thus, hemoglobin transports oxygen in the blood and myoglobin transports oxygen in the muscle. Without hemoglobin, some oxygen gas can dissolve in blood plasma, but in terms of quantity, the amount is next to zero. So iron is very important for all cells day-to-day needs.

Iron Needs

How much iron doe athletes need

Different people need different amounts of iron. Not that that should be any sort of news to anyone – different people need differing quantities of many, if not all, nutritional components. However, needs are a bit more pronounced when it comes to iron, so it deserves some special attention.

For adult men, the RDA for iron is 8 mg, and this is the same as the daily value (DV) for nutritional supplement labels unless the product is intended for pregnant women or children. For adult women, there are different classifications for menstruating and non-menstruating, pregnant, and lactating women. Adult, menstruating women need 18 mg of iron per day, pregnant women need 27 mg of iron per day, and lactating women need 9 mg of iron per day.

All of the above needs are nearly doubled for vegetarians. This is because of heme and non-heme iron. Heme iron is better absorbed and found in meats. Non-heme iron is found in plants, which also contain a number of anti-nutrients that limit iron absorption.

Needs are increased again for athletes. Depending on the type of activity, iron needs are 1.3 – 1.7 times greater. Runners need the most iron, as red blood cells are actually damaged from repeated foot strikes on the ground (called foot strike hemolysis), so more iron is needed to form new red blood cells. Therefore, if you are a pregnant, running, vegetarian woman, you may need up to 82.6 mg of iron per day – more than 10x the DV!

Of note, general recommendations are to avoid iron supplementation unless you get your iron levels measured and are observed as having a need. In the ferritin discussion, iron toxicity is mentioned, and this is possible when ingesting large quantities of iron, but the tolerable upper limit (TUL; greatest amount unlikely to cause any adverse effect) for iron is 45 mg because more than that can cause gastrointestinal distress. The reason that you may see iron supplements discouraged is because most iron supplements contain anywhere from 30 to 1,000 mg of iron. These types of supplements are designed to correct iron deficiency and anemia – they are not for supporting healthy iron levels as a small aid, such as with multivitamins. A person already of good iron status that begins supplementing several hundred milligrams of iron daily will very likely experience side effects.

Can Iron Improve Endurance Performance?

iron needs of runners

Because iron is a functional component of oxygen-transporting hemoglobin, it is rational to theorize that it can improve endurance performance by improving oxygen consumption. In fact, this is exactly the way it is; when iron status is poor.

Unfortunately for endurance athletes, most are deficient in iron. Fortunately, it’s an easy fix – eat some more iron.

In iron deficient runners, 4 weeks of iron supplementation (975 mg per day of iron sulfate) corrected the iron deficiency and improved their run times vs control participants during a graded treadmill running test. The results are similar for cycling. 4 weeks of iron supplementation significantly improved 15km cycling times compared to placebo.

How to Meet Iron Needs

iron for the endurance athlete

Because plant foods containing iron also inhibit iron absorption, the best sources are animal sources, particularly red meat, shellfish, and fish. Of course, iron from plants will still make a contribution to meeting total daily iron needs, but it is only about half as effective. Here are 2 sample days focused on iron-rich and mostly iron-poor foods, respectively:

Iron-Rich (15mg, 10.25mg functional)

  • Breakfast (4.5mg, 3.25mg functional)
    • 2 egg omelet with spinach & cheese, 2 slices of toast w/jam
  • Snack (2.5mg, 1.5mg functional)
    • 1 granola bar, 1oz dark chocolate
  • Lunch (3mg, 2mg functional)
    • 4oz chicken, 2oz hummus, 1oz pistachios
  • Snack (1mg, 0.5mg functional)
    • ¼c raisins
  • Dinner (4mg, 3mg functional)
    • 4oz steak, ½c broccoli, 1c brown rice
 
Iron-Poor (8.8mg, 4.9mg functional)
  • Breakfast (2mg, 1mg functional)
    • 2 pancakes, 1c yogurt and ½c berries
  • Snack (0.3 mg, 0.15mg functional)
    • 1 banana, 1oz cheese
  • Lunch (3mg, 2mg functional)
    • 1 tuna salad sandwich, ½c cucumber slices
  • Snack (1mg, 0.5mg functional)
    • 3c popcorn, 1 apple
  • Dinner (2.5mg, 1.25mg functional)
    • 1c vegetable curry, 1c rice

Both examples would be considered at least moderately healthy based on food selection and variety. Both examples are about 1800 calories for simplicity’s sake and generalizability. However, the two contain very different quantities of iron. One is clearly sufficient for most people, while the other is clearly insufficient for anyone, even a child, despite containing a few decent sources of iron in tuna, bread, and rice. The average of the two would only nearly be sufficient for men and post-menopausal women at ~7.5mg.

For athletes, you may be thinking, “well I eat way more than that!” This may very well be true, and I hope it is the case. You need to eat more calories to support your training. However, your iron needs are also greater. Simple extrapolation would suggest the risk for low iron intake is maintained based on increased need. With 50% greater intake, the diets would contain ~2700 calories and 7.5-15mg iron. The mean iron intake would be ~11mg, but needs would be ~12mg at minimum. You can clearly see from this example why iron is so important for women, who tend to eat less, but have much greater need.

One Potential Solution: Limited Iron Supplementation

foods containing iron

Previously discussed was the apprehension of professionals to encourage iron supplementation without tests being conducted first. While this is certainly the safest approach, it’s not terribly difficult to tally up an estimate of iron intake based on common foods consumed and looking at the National Institutes of Health references here or here. This way you can figure out about how much iron you’re getting before beginning any sort of iron supplementation. If you are anything except definitely in excess of your needs based on sex, activity, and pregnancy status, there is very little potential for danger from small quantities of supplemental iron, as the TUL is 45mg after all.

This is why EndurElite has included small amounts of iron in ElectroElite. It is population-specific fortification or enrichment, just like the government does with milk and vitamin A, cereals and B vitamins, and salt and iodine. There is an obvious micronutrient insufficiency, so we’ve inserted a little bit of iron (2mg) into a staple “food,” in this case an electrolyte supplement. It just made too much doggone sense!
 
References

  1. McClung, J. P., Karl, J. P., Cable, S. J., Williams, K. W., Nindl, B. C., Young, A. J., & Lieberman, H. R. (2009). Randomized, double-blind, placebo-controlled trial of iron supplementation in female soldiers during military training: effects on iron status, physical performance, and mood–. The American journal of clinical nutrition90(1), 124-131.
  2. Toxqui, L., & Vaquero, M. P. (2015). Chronic iron deficiency as an emerging risk factor for osteoporosis: a hypothesis. Nutrients7(4), 2324-2344.
  3. Chandra, R. K., & Saraya, A. K. (1975). Impaired immunocompetence associated with iron deficiency. The Journal of pediatrics86(6), 899-902.
  4. Weinberg, E. D. (1978). Iron and infection. Microbiological reviews42(1), 45.
  5. Sports Dietitians of Australia. (2009). Iron Depletion in Athletes Fact Sheet. Retrieved from: https://www.sportsdietitians.com.au/wp-content/uploads/2015/04/Iron_depletion_in_athletes.pdf
  6. Lampe, J. W., Slavin, J. L., & Apple, F. S. (1986). Poor iron status of women runners training for a marathon. International journal of sports medicine7(02), 111-114.
  7. Nickerson, H. J., & Tripp, A. D. (1983). Iron deficiency in adolescent cross-country runners. The Physician and sportsmedicine11(6), 60-66.
  8. Rowland, T. W., Deisroth, M. B., Green, G. M., & Kelleher, J. F. (1988). The effect of iron therapy on the exercise capacity of nonanemic iron-deficient adolescent runners. American Journal of Diseases of Children142(2), 165-169.
  9. Hinton, P. S., Giordano, C., Brownlie, T., & Haas, J. D. (2000). Iron supplementation improves endurance after training in iron-depleted, nonanemic women. Journal of Applied Physiology88(3), 1103-1111.
  10. Hunding, A., Jordal, R., & Paulev, P. E. (1981). Runner's anemia and iron deficiency. Acta Medica Scandinavica, 209(1‐6), 315-318.
  11. 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 nutrition61(1), 30.

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