What are the dangers of EPO and blood loading? Or if this is such a great deal, why weren’t we all born with hematocrits of 50%?

When you add more solid matter to a solution it thickens. Blood has to circulate through some very small blood vessels in the body. Capillaries are the smallest vessels but there are some fairly small arteries that go to important parts of the body such as the heart and the brain. There are numerous factors that can encourage the blood to clot within the body or that can act to impair circulation. The primary cause of death in most Western countries is blood clots-the ones that cause heart attacks and the ones that cause strokes. When blood gets thick enough it starts to circulate poorly and sludges or tends to thicken severely, especially in the smaller vessels. Your blood wouldn’t be thick even if you boosted your hematocrit from 40 to 48%. However, if you boosted your hematocrit and then became dehydrated you could be in trouble. Losing enough water from the blood to raise your hematocrit into the mid 50’s can cause thickening to occur, and you can face a significant health risk.

EPO is rumored to have caused more than two dozen deaths. The largest group of deaths that was attributed to EPO occurred in five Dutch cyclists in 1987, the year that EPO was introduced in Europe.

EPO use could kill by producing high hematocrits coupled with exercise induced dehydration, enough sludging to cause a shortage of blood to part of the heart, and then a fatal cardiac arrhythmia (an irregular heartbeat such as ventricular fibrillation) or heart attack. Stroke is another potential cause of death. Most strokes are also caused by blood clots.
An athlete also could have digestive system problems. The stomach and especially the intestines have significantly decreased blood flow during intense exercise, even in your average athlete. This accounts for some of the bowel symptoms that runners often get. The blood vessels nourishing the intestines are also a site that can develop blood clots in older individuals. There are several cases of Iron Man distance triathletes with significant internal bleeding and even bowel surgery after races. EPO or blood loading would increase that risk.

Blood loading has a slightly different risk profile. Because the amount of additional blood that someone receives can be measured exactly there is not as much danger in overshooting and sludging or clotting. In one of the blood loading studies that gave participants 2 units of their own blood, hematocrits only went up by 2 or 3 percentage points (but 5K times dropped by 30 seconds in trained runners!). However there is a very minor risk of human error resulting in your receiving someone else’s blood or even your own blood being contaminated. And of course there are potential complications associated with IV’s and the fluid given along with the blood. These days most blood boosting is done with Epo because it’s much less complicated. It’s given by a simple injection two to three times per week just like a diabetic takes insulin.