Chlorella and a few other algae are the only plant sources that contain any significant amounts of this vitamin. If you're a vegan, this vitamin is essential because it is not found in any other vegetable source. Lack of vitamin B12 is a common problem in ALL VEGAN DIETS. Deficiencies of B12 can lead to pernicious anemia and impairment of brain and nerve tissue that may result in permanent neurological damage. A major concern with B12 deficiency is that it is not easily recognized before it has already caused physiological damage.