Dr. Art Siegel is a graduate of Harvard Medical School, a respected professor there, and a former marathon runner. He published an article in the American Journal of Cardiology that shows that after a marathon, runners have extremely high blood levels of clotting and inflammatory factors that are associated with an increased risk for heart attacks. The media concluded from this study that running marathons can cause heart attacks and kill you.
Running damages muscles, and damaged muscles release chemicals such as CPK and von Willebrand factor that cause clotting. Clots can block the flow of blood to the heart to cause heart attacks. Dr. Siegel showed that these clotting factors are released from muscles during a marathon. However, running also produces antifibrinogens that prevent clotting. Furthermore, marathon runners seldom have plaques in their arteries, and we know that arteries narrowed by plaques are the most likely to be blocked by clots. The media should not have reported that Dr. Siegel's study shows that running marathons causes clots and heart attacks, because it doesn't.
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