Anemia in Athletes: Causes, Training Load, and the Role of Medications
Fatigue, heavy legs and stalled progress are often blamed on overtraining. Sometimes the real cause is in the blood. Anemia and iron deficiency are common in endurance athletes, women and people who restrict calories, and certain medications and performance drugs can also change blood counts. Our editors walk through the mechanisms and what testing can reveal.
What anemia means for an athlete
Anemia is defined as a hemoglobin concentration below the reference range for age and sex. Hemoglobin carries oxygen from the lungs to working muscles, so even a moderate drop reduces maximal oxygen uptake and endurance capacity. Athletes often notice it first as a rise in heart rate at familiar paces and an inability to finish intervals.
Iron deficiency is a broader problem. It progresses in stages: first iron stores (measured as ferritin) fall, then the iron supply to developing red cells becomes limited, and only at the end does hemoglobin drop. Many athletes sit in the earlier stages, technically not anemic but still underperforming.
Iron deficiency without anemia can still affect performance and well-being. Several trials in iron-depleted women showed improved endurance adaptation after iron repletion, even when hemoglobin was normal at baseline.
Other forms of anemia exist too, such as those caused by vitamin B12 or folate deficiency, chronic disease or inherited conditions. A proper workup by a physician is needed to distinguish them, because the treatment differs.
How training itself affects the blood
Endurance training expands plasma volume faster than it increases red cell mass. The result is a lower hemoglobin concentration on lab tests, even though total hemoglobin in the body may be higher than before. This so-called dilutional pseudoanemia, or "sports anemia," is a normal adaptation, not a disease.
True losses also occur. Repeated foot strikes during running can damage red cells in the capillaries of the soles, a process called foot-strike hemolysis. Small amounts of iron are lost through sweat, and some athletes experience minor gastrointestinal bleeding during long, intense efforts, particularly in the heat.
A key regulator is hepcidin, a hormone produced by the liver. After strenuous exercise, inflammation raises interleukin-6, which in turn raises hepcidin for several hours. Hepcidin blocks iron absorption in the gut, so iron taken right after a hard session may be absorbed less efficiently.
Altitude camps add another layer. Hypoxia stimulates red cell production, which increases iron demand. Athletes starting a camp with low ferritin may not get the hematological benefit they expect.
Nutrition, energy availability, and risk groups
Low energy availability, meaning too little food relative to training load, is a major driver. The International Olympic Committee's consensus statement on Relative Energy Deficiency in Sport (REDs) lists impaired iron status and hematological changes among its consequences.
Women of reproductive age are at higher risk because of menstrual losses. Vegetarian and vegan athletes may consume enough total iron but in the non-heme form, which is absorbed less efficiently than iron from meat and fish.
- Female endurance athletes, especially runners and triathletes
- Adolescents during growth spurts
- Athletes in weight-class or aesthetic sports who restrict calories
- Plant-based athletes without careful meal planning
- Frequent blood donors and athletes training at altitude
Combining iron-rich foods with vitamin C sources improves absorption, while tea, coffee and high-calcium foods eaten at the same meal can reduce it. Timing iron-rich meals or prescribed supplements away from those foods, and ideally in the morning or away from the post-exercise hepcidin peak, is a practical step.
Medications and performance drugs that affect blood counts
Pharmacology can push blood values in both directions. Several common medications are associated with lower hemoglobin or iron status, while some performance-enhancing drugs raise red cell mass to potentially dangerous levels.
| Substance or group | Typical effect on blood | Why it matters |
|---|---|---|
| NSAIDs (e.g., ibuprofen) used frequently | Possible GI blood loss | Can contribute to iron deficiency over time |
| Proton pump inhibitors | Reduced iron and B12 absorption | Long-term users may need monitoring |
| Metformin | Lower vitamin B12 over time | Can lead to macrocytic anemia |
| Anabolic steroids, testosterone | Raised hematocrit | Thicker blood, higher thrombosis risk |
| EPO and analogues | Strongly raised hematocrit | Prohibited; linked to stroke and clotting |
| Stopping androgens | Fall in hemoglobin | Can unmask fatigue and low counts |
Erythropoietin misuse in endurance sport is a well-documented example of how blood manipulation can be lethal; excessively thick blood increases the risk of clots, heart attack and stroke. These substances are banned by WADA and in the US are prescription-only drugs.
Testosterone and anabolic steroids stimulate red cell production. People who use them often show high hematocrit, and when they stop, values can drop, sometimes below baseline while the body's own hormone production recovers. Any such situation calls for medical evaluation, not self-management.
Testing and what to discuss with your doctor
A basic panel includes a complete blood count, ferritin, serum iron, transferrin saturation and often C-reactive protein, because inflammation raises ferritin and can mask deficiency. B12 and folate may be added if red cells are larger than normal.
Ideally, blood should be drawn in the morning, rested, and not within a day after a very hard session or race, which can distort results. Repeating tests at the same time of season gives a more useful trend.
Sports medicine practitioners often use higher ferritin thresholds for athletes than general reference ranges, but cut-offs vary. Your physician will interpret values in context, including symptoms and training history.
Iron supplementation should be targeted. Taking iron without a confirmed need risks iron overload, especially in people with hereditary hemochromatosis, a relatively common genetic condition among people of Northern European descent.
Editorial Team Conclusions
Anemia and iron deficiency in athletes arise from a mix of plasma expansion, real iron losses, hormonal regulation, insufficient energy intake and sometimes medications.
Not every low hemoglobin reading is a problem, and not every tired athlete is iron deficient. Testing and professional interpretation are essential before any treatment.
Performance drugs complicate the picture in the opposite direction, raising red cell mass to unsafe levels and creating rebound problems after withdrawal.
You may also find useful our articles on how to read a complete blood count, on Relative Energy Deficiency in Sport, and on why hematocrit matters for heart health.
References
- Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. Eur J Appl Physiol. 2019;119(7):1463–1478.
- Peeling P, Dawson B, Goodman C, Landers G, Trinder D. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. Eur J Appl Physiol. 2008;103(4):381–391.
- Clénin G, Cordes M, Huber A, et al. Iron deficiency in sports — definition, influence on performance and therapy. Swiss Med Wkly. 2015;145:w14196.
- Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57(17):1073–1097.
- Pedlar CR, Brugnara C, Bruinvels G, Burden R. Iron balance and iron supplementation for the female athlete: a practical approach. Eur J Sport Sci. 2018;18(2):295–305.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
