Iron and the endurance athlete.

Within your body are specialized molecules that carry the oxygen that is essential for life. In the blood this is known as hemoglobin and in the muscle it is called myoglobin. Iron is an essential component of these molecules because oxygen binds specifically to the iron atoms that they contain. When iron stores fall, oxygen delivery and aerobic output suffer, often before anemia ever shows up on a standard Complete Blood Count (CBC).

A CBC reports several measures that bear on iron. First we have Red Blood Cells (RBCs) which give our blood its color and travel through our cardiovascular system while carrying oxygen. The red blood cells each contain approximately 270 to 280 million oxygen carrying Hemoglobin (Hb) proteins. Hematocrit (Hct) is the ratio of your blood that is made up of red blood cells.

Other numbers give us more detail about your blood cells. Red Blood Cells are graded based on size (Mean Corpuscular Volume, or MCV). Small cells are common in iron-deficiency anemia, and large cells are often due to vitamin deficiencies. We can also see the amount of hemoglobin in each cell (Mean Corpuscular Hemoglobin, or MCH) and too little and too high are again typically caused by iron deficiency or vitamin deficiency respectively.

Because your body is very good at regulating itself, we often do not see changes in these values until your iron stores are running very low. This is why measuring ferritin, the storage form of iron, is essential to managing individual iron status.

Low iron is common in athletes. A 2019 review of iron in athletes reports iron deficiency in about 15 to 35 percent of female athlete groups studied and about 5 to 11 percent of male groups (Sim et al., 2019).

Endurance athletes are especially prone to low iron. Repeated foot strikes can damage red blood cells (foot-strike hemolysis). Iron is also lost through sweat and the gut, and hard exercise raises hepcidin, a hormone that blocks iron absorption. Together these can drain stores faster than diet replaces them. The result is often iron deficiency without anemia: low ferritin with normal hemoglobin. It can still leave you tired and slow to recover.

Hepcidin also limits how much iron the gut takes up from tablets. That is one reason oral iron can work slowly for athletes in heavy training.

The research is consistent on iron status. In iron-deficient athletes, iron treatment raises ferritin and the other iron measures. (Burden 2015, Br J Sports Med)

Many athletes start with oral iron as it is the easiest and most cost-effective route. However, oral iron supplementation can often lead to nausea, constipation, and GI distress (Tolkien et al., 2015). Iron that the gut doesn't absorb passes on to the colon, where it can change the mix of gut bacteria and irritate the gut (Seyoum et al., 2021). These symptoms are often compounded by athletes increasing their iron dose in an effort to see faster results. If you decide to take oral iron, we strongly suggest that you work with a registered dietitian to create an individualized plan.

IV iron is a terrific solution when labs show your iron is low, especially if pills haven't worked, aren't tolerated, or are too slow for a training block or event. An infusion bypasses the gut and replaces a measured dose directly, which results in stores that refill much faster than with pills. In a study of 27 highly trained distance runners with low or borderline ferritin, IV iron raised iron stores within six weeks (Garvican et al., 2014).

Iron is not a prohibited substance. The rule concerns the method. Under the WADA 2026 Prohibited List, IV infusions or injections of more than a total of 100 mL in a 12-hour period are prohibited at all times, in and out of competition, unless they are legitimately received during hospital treatment, surgery, or clinical diagnostic investigations. Above that volume, a clinic infusion requires a Therapeutic Use Exemption (TUE). USADA's guidance on IV infusions notes that the limit applies in a doctor's office or clinic, and that it applies even when the substance being infused is permitted.

For athletes in a testing pool, we build the protocol around that line, adjusting dose, volume, and delivery to stay within WADA's infusion limits. Where the deficit allows, eligible athletes can replete iron without filing for a TUE. We document the dose and volume in full, so the record is there if it's ever asked for.

College athletes compete under NCAA rules. The NCAA is not a WADA Code signatory and keeps its own list of banned substances and methods, so its rules can differ.

We'll always point you back to your sport's anti-doping authority for the final word, and time treatment around your testing and competition calendar.