1. Fatigue and poor performance may begin to appear in the second stage of deficiency, when not enough iron is present to form the molecules of blood protein that transport oxygen to the working muscles.
    到了缺铁的第二阶段，就会出现疲倦和力不从心，此时体内已没有足够的铁来形成血蛋白分子，将氧输至运动着的肌肉。