What depletes vitamin B12?

Your body needs B12 to have brain and nervous system functions. B12 is commonly used for the metabolism of a cell, DNA synthesis / regulation, and energy production (from fatty acids). Some people can also have a disorder (perniscious anemia) where their bodies cannot process B12, or their bodies use it up too fast. If a person also has a certain type of tapeworm, the parasite would use up the B12 in their body.