Iron

Ever wonder why iron matters so much for performance? It’s what carries oxygen through your body, fueling the energy and strength you need to train, compete and recover.

When iron runs low, fatigue often follows, primarily affecting endurance and, to a lesser extent, power. Athletes and active people are especially at risk for iron deficiency and the healthiest range for you may actually be on the higher side of normal. The good news: iron depletion can often be managed with food or supplements. A doctor can check your levels through blood testing and guide the best plan forward.

Hilary Stellingwerff shares her personal journey with iron deficiency

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Iron: Function, Needs and Sources

Iron is a key mineral that helps your body carry oxygen, helping you perform at your best.

Low iron can leave you feeling drained, limit your endurance and hold you back from reaching your performance goals.¹ Iron deficiency in athletes is not rare, occurring in 15-37% of female athletes and 5-11% of male athletes.^1,2 What’s tricky for an athlete is that your iron levels might be in the “normal range” on bloodwork, but still low enough to impact your athletic performance.

In this deep dive, we’ll explore why iron is essential, how to spot potential issues and ways to address low iron and maintain optimal levels.

Iron needs differ by age and life stage.

The Recommended Dietary Allowances (RDAs), how much of a nutrient most people should aim for each day, are specific to the United States and international guidelines may vary.³ Your body gets iron from the foods you eat.⁴

RDAs for Iron in milligrams (mg):⁴

Iron Content in Select Foods

Heme iron sources

Non-heme iron sources

Heme iron sources may be more easily absorbed into the body than non-heme iron sources. To improve absorption, you can pair non-heme iron sources with a food or beverage containing vitamin C.⁵ Sources of vitamin C include:

• Citrus (orange, lemon)
• Berries
• Bell peppers

Some nutrients and compounds in food interfere with iron absorption:

• Calcium (dairy, supplements)
• Polyphenols (tea, coffee, cocoa)
• Phytates (whole grains, beans, nuts & seeds)

It is best to consume iron-rich meals or iron supplements separately from meals that contain these nutrients. However, it is most important to get iron into your diet, regardless of other dietary confounders.

Iron Deficiency

Active people are at risk of developing low iron levels and iron deficiency.

Exercise increases the risk of iron deficiency due to the various ways we lose iron. Exercise increases hepcidin, a hormone that decreases the ability to absorb iron, with hepcidin levels peaking 3-6 hours following exercise.^6-8 Running specifically causes a very small but repeated breakdown of red blood cells that occurs as one’s feet hit the ground repetitively, spilling iron into circulation; this process is called foot-strike hemolysis.⁹ Other ways we lose iron are through our sweat and from microbleeding in the gastrointestinal tract and urinary system.¹⁰

In a study of 1880 competitive and elite female athletes, 40.7% of those who had experienced heavy menstrual bleeding also reported a history of iron deficiency anemia.¹²

The risk of iron deficiency is higher in:^{1, 13-15}

• Female athletes

• Pregnant athletes

• Those following a vegetarian or vegan diet

• Those with low energy availability

• Those participating in running and endurance sports

Checking Iron Levels

Iron status can be assessed through bloodwork.

Iron is stored in the body within a protein called ferritin, which is an important indicator of iron status. Athletes have a high turnover of iron, so they often benefit from having more iron stored to keep up with physiological demands. A ferritin level that is considered “normal” may be too low to support optimal athletic performance. In general, athletes are encouraged to maintain a ferritin level above 35 μg/L; the ideal threshold varies due to performance demand, assay method and ongoing debate within sports science.^15-18

At a minimum, iron, ferritin, hemoglobin and transferrin saturation should be measured to assess iron status. Ferritin levels can also be elevated due to systemic inflammation, thus checking ferritin alone may be misleading. While not required, C-reactive protein (CRP) can help identify cases of elevated ferritin due to inflammation, rather than reflecting adequate iron stores.¹⁹

Iron bloodwork interpretation^{1, 19-22}

Iron screening is recommended twice per year for female athletes and annually for male athletes.^{1, 13}

Not all cases of low iron are symptomatic, and you don’t need to wait for symptoms to appear to seek advice. More frequent screening (three or four times per year) is recommended for those with additional risk factors:¹

• History of iron deficiency
• Dietary pattern low in iron
• Relative Energy Deficiency in Sport (REDs)
• Performance decrements
• Menstrual cycle concerns (absent or irregular periods, heavy menstrual bleeding)
• Unexplained fatigue
• High training demand
• Plan to train at altitude

It is important not to supplement iron without checking iron status and following your physician's guidance; taking too much iron can be toxic to your organs.

Additionally, if low iron reserves are not the underlying cause of your fatigue or other symptoms, taking an iron supplement may not address your performance and health concerns.

When iron is depleted, oral iron supplementation for 4-12 weeks can increase ferritin levels.²⁵

In addition to improving iron stores, oral iron supplementation may improve VO₂max (a marker of endurance performance) in those with iron deficiency.²⁶

There are many forms of iron supplements available for use. Ferrous iron salts, such as ferrous sulfate, ferrous gluconate and ferrous fumarate, are popular choices for repletion. Additional forms of iron include ferric formulations, and other forms such as carbonyl iron.²⁷ These supplements can have gastrointestinal side effects, including nausea and constipation. Alternate-day supplementation may be one approach you can adopt to minimize side effects, which has the potential to increase compliance and consistency to effectively improve iron status.^28,29 Your healthcare team can help you find a balance between the ideal iron supplement form, dose and timing to improve iron and minimize side effects.

Iron supplements are best taken in the morning or in the 30-minute window right before or after exercise.^30-32 This is when hepcidin is at its lowest. However, the best time of day for you to take your iron supplement will depend on what minimizes any side effects and allows you to be consistent. Re-testing your iron levels a few months after starting supplementation is important for assessing changes.^1,22 

In some cases, it is recommended to have iron infused directly into your blood. A physician can provide guidance on whether and when this intervention is needed.