Iron Deficiency in Runners

Ferritin is a blood protein that is your body’s preferred storage form of iron, which it releases as necessary. Around 25 percent of all the iron in your body is typically contained in ferritin. The demand for iron goes up when you’re training or racing because it’s the building block for hemoglobin in the bloodstream, which delivers oxygen from the lungs to your muscles via red blood cells. Iron is also needed to regulate myoglobin, a protein found in muscles that binds to and releases oxygen, and cytochromes, a key catalyst of energy production. It plays a part in immunity, DNA synthesis, pH balance, and many other processes too. Unlike some other micronutrients, your body cannot make its own iron, so you have to take it in through food and/or supplementation.

According to a study on female basketball players, “Athletes experience disturbances of systemic iron homeostasis, especially during training periods characterized by intense training loads.” The authors stated that iron in female athletes can be twice as low as in sedentary groups. It’s also arguably more common. A review published in the European Journal of Applied Physiology stated that five to 11 percent of male athletes tested in previous trials were low on ferritin, which is an indicator for inadequate iron. This rose to a whopping 15 to 35 percent of female athletes. Other studies have pegged these numbers even higher, suggesting that up to 56 percent of female endurance athletes have insufficient iron stores. 

So why is this? We can lose iron through sweat and urine, the GI tract, frequent use of NSAIDs, and a phenomenon known as foot-strike hemolysis. This occurs when red blood cells in the feet are destroyed as you pound the pavement or trail, which not only results in the loss of iron, but also needing to utilize more to repair the damage. That might explain why runners, basketball players, and athletes in other sports that involve a lot of ground contact have higher rates of deficiency. 

There are several reasons why low iron might affect more female athletes than males. First, some can be lost during monthly menstruation. Second, I see more women who are on vegan or vegetarian diets. While you can find iron in some plant-based sources, it’s more difficult to absorb because it’s in the non-heme form. Whereas fish, meat, and poultry all contain the more available form, heme iron. Those who eat fortified foods find it easier to boost their intake. The overall quantity of food female athletes eat may be significantly less than a larger male athlete making it harder to get sufficient iron. 

The authors of the basketball study wrote that “Insufficient reserves of iron in the body can reduce athletic performance, which may be manifested as fatigue, exercise intolerance, or even cognitive function impairment.” I often hear clients complain of not being able to hit or maintain their target paces in training, feeling like they’re exerting more effort than usual, hitting the wall sooner, and generally feeling heavy and lethargic. They might also notice decreased adaptation to their training and failure to recover fully between sessions. Increased resting and active heart rate, dizziness, and shortness of breath during exercise can become issues too. 

Certain sessions like sprints and intervals can become harder because power output declines and time-to-exhaustion is reduced when ferritin levels are low. Some athletes might experience irritability and other mood disturbances, find it hard to focus during workouts, or become apathetic and lose interest in training altogether. They could also start struggling with niggling injuries and more frequent bouts of illness. In these ways, iron deficiency can be mistaken for chronic overtraining, as many of the symptoms are the same.