Why Iron is a key nutrient for athletes

Iron is an essential mineral that plays many important roles in our body. Most notably, it is a component of hemoglobin, which helps deliver oxygen to the body. Many of the body’s energy-producing enzymes also need iron in order to function properly. Iron also helps your cells make ATP (your body’s main energy source) and supports normal cell growth. Because of this, getting enough iron is important. Athletes and active people should especially care about getting enough to support their overall wellbeing and optimize their performance.

In this blog post, we will discuss

• Possible risks of having low iron levels

• Why athletes are at risk for suboptimal iron levels

• Strategies to improve iron levels

How do I know if I have low iron?

Physical signs and symptoms may point to an iron deficiency. However to confirm this, your primary care provider should order a blood test.

Signs of iron deficiency may include:

• Unexplained fatigue

• Weakness

• Impaired endurance and performance

• Frequent headaches

• Lightheadedness, dizziness

Getting a blood test is the best way to verify your iron status

Your primary care provider may order a blood test to verify your iron status. This most often includes Complete Blood Count (including hemoglobin, red cell count, etc) and Ferritin (iron stores), but may also include Iron studies (including transferrin and transferrin saturation). Reference ranges may vary depending on region and population. In Ontario, Canada (as of 2024) Ferritin is reported as such:

• Results less than 30 µg/L for adults (≥18 years of age) will be flagged as low.

• Results less than 20 µg/L for children and adolescents (<18 years of age) will be flagged as low.

• Results greater than or equal to 600 µg/L will be flagged as high for all ages.

See more about ferritin reference ranges in Ontario here.

While ferritin is often used to assess iron status, it is important to note that it is not always the most reliable indicator. It is an acute phase reactant and therefore may be impacted by inflammation (Inflammation may occur when someone has an illness or infection). For example, someone's ferritin may be falsely elevated if they get their labs drawn while they have an upper respiratory infection. Other labs, such as CRP - a general inflammatory marker, and/or iron studies (including serum iron, transferrin and transferrin saturation) may be ordered to better interpret iron levels, especially those with certain health conditions such as Inflammatory Bowel Disease (IBD).

"Low iron" is a relatively broad term. While low iron is often associated with anemia, it is important to note that this is not always the case. Though defining specific types of nutritional deficiencies and anemias is beyond the scope of this topic, below is a simplistic way to view it for the purpose of this article:

• Low/Suboptimal Iron: Iron stores are getting low

• Anemia: Hemoglobin is low. This could be from low iron, b12, blood loss or chronic disease

• Iron deficiency anemia: Hemoglobin and iron stores are both low

Who may be at risk for low iron?

Endurance Athletes

Circulating levels of a hormone called hepcidin is often high after endurance exercise. Hepcidin is a crucial part of iron homeostasis, and its role is to regulate the body's iron levels by controlling iron entry into the bloodstream. Hepcidin levels rise during inflammation to keep iron away from pathogens, or when there is too much iron in the body to prevent iron overload. In other words, increased hepcidin activity reduces iron absorption.

Overall, research suggests that hepcidin levels are elevated within a few hours after strenuous exercise. They peak around 3 hours after exercise, and remain elevated for around 3 - 6 hours after exercise (1). This elevation in hepcidin puts endurance athletes at risk for suboptimal iron levels.

Endurance athletes, particularly long distance runners may be prone to a condition called "red cell haemolysis" also known as "Foot-strike haemolysis" which is where strenuous activity, such as the repetitive impact of foot striking the ground leads to the destruction of red blood cells. Repeated blood cell destruction could lead to iron deficiency over time, however "foot strike hemolysis" is generally mild and not a concern for most endurance athletes. One study found that ultra-marathon runners hemoglobin and red blood cell count were not significantly impacted after completing a 60 km event (2).

Those with malabsorption conditions

This may include conditions such as Inflammatory bowel disease, and celiac disease that may impair the body's ability to absorb iron and other micronutrients if left untreated. In these cases, athletes should ensure to treat their condition with the support of their healthcare team as this will enable their body to better absorb iron.

For example, someone with celiac disease who is adhering to a gluten-free diet and eats a variety of foods may have normal iron levels and not need additional iron supplementation. But someone else with celiac disease who has frequent gluten exposures could be more likely to have suboptimal iron levels as this can damage their small intestine overtime. See "Sports Nutrition for Celiac Athletes" for more information.

Females

Those who menstruate are more likely to have suboptimal iron levels, where they lose more iron through their blood. Because of this, females have higher iron requirements:

Recommended Iron intake for Males aged 19 - 50: 8 mg per day

Recommended Iron intake for Females aged 19 - 50: 18 mg per day

Those following plant-based diets

This may include those who practice veganism, or those who follow a vegetarian diet. Plant-based foods contain non-heme iron which is absorbed less efficiently than heme iron (the iron found in animal-based foods).

Because of this, the daily recommended iron intake is 1.8 x higher for vegetarians based on Health Canada Dietary Reference Intakes.

How to treat suboptimal iron levels.

Okay, so you found out you have low iron levels - what do you do about it now?

There are multiple different approaches to increase your intake of iron such as through dietary or supplemental means. In some severe cases, intravenous iron may be used - but this must be monitored closely by a medical practitioner.

Diet

The first line approach, particularly in cases where athletes are not anemic, or when they have mildly low iron stores.

Red meat (ex: beef) is a well known source of iron, but iron can also be found in various plant-based foods.

Other food sources of iron include:

• Beans

• Lentils, dal

• Fortified wheat products (cereals, breads, pastas)

• Dark leafy greens

• Textured vegetable protein (TVP)

• Wheat germ

• Hemp seeds

Vitamin C

Vitamin C rich foods may help enhance iron absorption, so try to eat iron rich foods with a source of vitamin C. Most fruits and vegetables are great sources of vitamin C. Some ways to incorporate vitamin C with iron rich foods include:

• Vegetable Chili

  • Iron source = Beans, textured vegetable protein (TVP)/or ground beef

  • Vitamin C source = tomatoes, bell peppers

• Lentil curry

  • Iron source = Red lentils

  • Vitamin C source = tomato sauce, broccoli, other mixed vegetables

• Oatmeal with berries, hemp hearts and wheat germ

  • Iron source = Wheat germ, hemp hearts

  • Vitamin C source = mixed berries

Oral Iron Supplements

Oral iron supplements may be helpful in cases where someone does not show significant improvement with iron rich foods alone, or in cases when an athlete has more severe iron deficiency and/or anemia. There are many different types of iron supplements available on the market offered in different formats (ie: liquid, capsule etc). It is important to note that different types of iron absorb differently. Below are two common examples for iron supplements commercially available:

Iron Salts

These include Ferrous sulphate or ferrous fumarate (ex: Palafer), and tend to be the most effective in improving iron levels. Digestive upset (ie: abdominal pain, cramping, constipation) is a common side effect with this formulation of iron.

If you experience GI upset, take the supplement with a snack (avoid high-calcium foods at the same time) and be sure to drink plenty of fluids throughout the day. Alternate day dosing (taking your iron every other day, instead of daily) has been shown to still improve iron stores, with less digestive upset (3).

Iron polysaccharides

Common options include Feramax and Polyride. These options are marketed for causing less GI upset, but tend to have a much less robust impact on iron levels. Because of this, they may not be the most ideal choice for those who have more severe iron deficiencies, or those with multiple risk factors. If you're recommended to take iron polysaccharides, you may have to take it for longer and/or take a higher dose.

Dosing for iron varies depending on the reason why you're taking it. It is best to consult with a healthcare provider to know how much you should be taking. Most iron supplements can be purchased over the counter, but you can ask your primary care provider to provide a prescription to ensure you're getting the suitable recommended dose.

Parenteral Iron (Injection or infusion)

Parenteral iron (by injection or infusion) results in a rapid increase in iron stores and is most often reserved for athletes with significant iron deficiency and/or anemia, especially in cases where iron does not improve by oral iron supplementation.

This mode of iron supplementation bypasses gut, therefore absorption is significantly improved. This must be ordered by a sports medicine physician or other medical practitioner (may also include family physician or nurse practitioner).

There is a high degree of variability to how long iron stores stay high, therefore athletes should still have their iron levels monitored after to determine their response to infusion because having iron levels that are too high can be dangerous.

What time of day should I take an iron supplement?

The best time to take it is whenever you're able to remember - however, taking iron earlier in the day may be more optimal.

Some evidence suggests that taking an iron supplement later in the afternoon after training can result in impaired absorption, this is because our hepcidin levels rise after training which inhibits iron absorption (4). One study suggests taking iron in the morning immediately after exercise may be most optimal for absorption (5), but may not be the most realistic for people. What is most important in the long term is taking iron consistently for an appropriate duration. Remember, iron absorption can also be enhanced by taking with vitamin C (see above), and by avoiding iron inhibitors (see below).

Iron Inhibitors

To optimize absorption when taking dietary iron, or oral iron supplements take it with vitamin C, and avoid taking it with iron inhibitors. Examples for iron inhibitors include:

• Teas, Coffees - contain compounds including tannins that may reduce iron absorption

• High Calcium Foods - Calcium competes with iron for absorption; therefore taking calcium supplements, or high calcium foods can make it harder for the body to absorb iron.

In short, avoid consuming dairy products (ie: milk, cheese, yogurt), fortified plant-based dairy alternatives, black teas and/or coffee around the time of taking an iron supplement.

Summary: Iron for athletes and active people

In my experience as a registered dietitian, low iron is a common concern I see in some clients. If you are at risk for low iron, working with a registered dietitian may help you prevent and/or treat iron deficiency while ensuring you're performing your best. Below are some key points to keep in mind.

• Those at risk for suboptimal iron levels or iron deficiency include: endurance athletes, females, those with malabsorption conditions, and vegetarians

• Treating suboptimal iron levels or iron deficiency includes: increasing food sources of iron, using an oral iron supplement or in severe cases, using parenteral iron (must be ordered by medical practitioner)

• If using an oral iron supplement, taking it earlier in the day before training may help absorption in the short term. However in the long term it is most important to take it consistently and for the appropriate duration.

Looking for guidance on how to fuel your body?

Let’s work together to create a plan that supports your goals and lifestyle. Check out the services I offer here for more information, and book a free discovery call here so we can chat about how we can use nutrition to meet your goals!

Hannah Donaldson, Registered Dietitian in Hamilton, Ontario Canada. Providing virtual services across Ontario.

Please note that the content provided in this blog post is for informational and educational purposes only. It is not intended to substitute professional medical advice, diagnosis or treatment.

References:

(1) Goto, K., Kojima, C., Kasai, N., Sumi, D., Hayashi, N., & Hwang, H. (2020). Resistance exercise causes greater serum hepcidin elevation than endurance (cycling) exercise. PloS one, 15(2), e0228766. https://doi.org/10.1371/journal.pone.0228766

(2) Lippi, G., Schena, F., Salvagno, G. L., Aloe, R., Banfi, G., & Guidi, G. C. (2012). Foot-strike haemolysis after a 60-km ultramarathon. Blood transfusion = Trasfusione del sangue, 10(3), 377–383. https://doi.org/10.2450/2012.0167-11

(3) von Siebenthal, H. K., Gessler, S., Vallelian, F., Steinwendner, J., Kuenzi, U. M., Moretti, D., Zimmermann, M. B., & Stoffel, N. U. (2023). Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study. EClinicalMedicine, 65, 102286. https://doi.org/10.1016/j.eclinm.2023.102286

(4) Solberg, A., & Reikvam, H. (2023). Iron Status and Physical Performance in Athletes. Life (Basel, Switzerland), 13(10), 2007. https://doi.org/10.3390/life13102007

(5) McCormick, R., Moretti, D., McKay, A. K. A., Laarakkers, C. M., Vanswelm, R., Trinder, D., Cox, G. R., Zimmerman, M. B., Sim, M., Goodman, C., Dawson, B., & Peeling, P. (2019). The Impact of Morning versus Afternoon Exercise on Iron Absorption in Athletes. Medicine and science in sports and exercise, 51(10), 2147–2155. https://doi.org/10.1249/MSS.0000000000002026