While moderate exercise improves cardiovascular health, marathons and ultra-long-distance running may damage RBCs, cause premature “aging,” and lower hematocrits. A recently published study collected pre- and post-blood samples from 23 long distance runners—11 (5 female; median age, 36 years) from a 40 km marathon and 12 (4 female; median age, 38 years) from an ultra-marathon 171 km in length. Based…