Vitamin B12 plays a key role in the normal functioning of the brain and nervous system, and for the formation of blood.rnrnInjection and patches are sometimes used in cases where digestive absorption is impaired, but there is evidence that this course of action may not be necessary with modern high potency oral supplements (such as 500 to 1000 µg or more). Even pernicious anemia can be treated en More..tirely by the oral route. Less