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The signs of Iron Deficiency and its effect on your performance


Feeling run down or generally fatigued lately? Not hitting paces in workouts that felt like no problem a few weeks ago? Resting heart rate higher than usual or increased shortness of breath while running? It could be a sign of iron deficiency or anemia. Because these symptoms sound similar to COVID, iron deficiency and anemia have been flying under the radar. While these terms are often used interchangeably, anemia is considered a more severe form of iron deficiency.

Iron is a mineral that your body needs–its most important role is to transport oxygen. Iron is used to make hemoglobin, a protein in red blood cells that carries oxygen from your lungs to your entire body. Hemoglobin uses about two-thirds of the iron in your body, so without enough iron, your body can’t make these vital red blood cells. Low iron is detrimental to your running performance because your muscles simply aren’t getting enough oxygen.

Athletes, and specifically runners, are at a higher risk for iron deficiency than sedentary individuals. Iron is lost through sweat, the GI and urinary tracts, and menstruation. Runners also breakdown red blood cells at a faster rate due to the force of foot strike while running. This phenomenon is called foot strike hemolysis.

A study in the early 2000s looked at ten triathletes to determine if the cause of hemolysis after endurance exercise was footstrike or just the endurance component of exercise itself. The study participants completed two one-hour sessions of running and cycling, one week apart at 75% of their VO2max. Their VO2max was determined one week prior to testing. Blood samples were collected before and immediately after each trial as well as one, six, and twenty-four hours post-exercise.

The authors found an increase in plasma-free hemoglobin concentration (an indication of hemolysis) following both running and cycling. However, the increase was significantly greater following running. As a result, the authors were able to conclude that footstrike impact was causing the greater hemolysis in this study.

While one training run can cause hemolysis, it’s unlikely to cause significant iron loss by itself. Multiple days of training with hard workouts and few rest days, on the other hand, can cause a cumulative loss that becomes significant. Distance runners are even more at risk if they follow a vegetarian or vegan diet due to the difference in iron absorption from plants compared to meat.

If you’re feeling any of these symptoms, don’t just start supplementing iron. You will need to consult your doctor and have bloodwork. More is not always better when it comes to iron supplementation–you can take too much. So if you’ve had unexplained fatigue and shortness of breath, and your COVID test is negative, it might be time for some bloodwork.

Telford RD Sly GJ Hahn AG et al. “Footstrike is the major cause of hemolysis during running”. Journal of Applied Physiology. 2003; 94(1): 38–42.

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