Low iron diets (vegan, vegetarian) are the most common cause for iron deficiency. Women with heavy menstrual bleeding can sometimes become anemic from this as well (and this is made worse with low iron diets!) Otherwise, the body really has no direct avenue for iron loss, other than negligible amounts lost in the course of cell shedding from the GI (gut) and genitourinary (urinary) tracts.
However, athletes are subject to a more insidious form of iron loss known as ‘foot strike hemolysis’ - sometimes known as runner’s anemia. This occurs when red blood cells are subsequently destroyed as they pass through the feet from the repetitive pounding of running. Of course, it takes a lot of running for this to happen, and a while to manifest.
Runners aren’t the only athletes susceptible to exercise induced hemolysis (destruction of red blood cells). This form of anemia has also been reported in rowers, swimmers and weight lifters, too.
However, runners typically wind up with about four times the amount of red blood cell destruction than other athletes do.
Footstrike anemia occurs most often in high mileage runners - or, in athletes whose training volume increases to a point where red cell production mechanisms are overwhelmed by training - think ‘two a day’ runs, marathoners and ultra runners - this is the group at greatest risk for foot strike hemolysis, sometimes referred to as hell strike hemolysis induced anemia.