An athlete is told that the use of erythropoetin could enhance their performance. Why could it have this effect and what types of athletes would benefit from its use?

Erythropoietin is a hormone produced in the kidneys that stimulates red blood cell production. People with chronic renal disease may be unable to produce sufficient erythropoietin to prevent anaemia developing, so synthetic erythropoietin has been developed to treat them. Unfortunately, synthetic erythropoietin has also been used as a doping agent in sports. By increasing the numbers of erythrocytes in the blood it will increase the amount of oxygen that can be transported to the tissues. This should be of benefit to athletes participating in endurance sports that require a high aerobic capacity. However, erythropoietin can cause an excessive increase in the viscosity of the blood (i.e. the blood becomes too thick) and that can limit the body's ability to distribute blood to the tissues. Erythropoietin use has been associated with sudden death in any athletes, particularly professional cyclists in Europe.