lack of Vit b12 leads to prenicuous anemia , commonly caused by a lack of absorption of b12, due to the difficency of intrinsic factor in your GI system. The advantage of taking it by Im is that you dont need the intrinsic factor for absoption in the muscle. if the deficency continues without treatment it may lead to nuropsychological problems ect.. there are several types of anemias and several diffrent causes , it all depends on your sysm and lab work up.
Anubis M.D.