Okay, I have no idea how any of this pertains to bodybuilding, but what the heck, doesn't hurt to share info: B12 is an easy vitamin to become deficient in if you don't follow a balanced diet, have any number of GI problems (anything from ulcers to IBS and everything in between, including celiac), are a vegetarian -- especially vegan -- or are older ... a deficiency in this vitamin can do some bizarre things to your health, ranging from a form of anemia to neurological problems (actually B12 deficiency is one of the first things they test for in suspected cases of dementia).