What would cause a vitamin B12 deficiencybesides anemia?

Vitamin B12 def. actually it's the other way around, Vit b12 def causes the anemia. B12 def occurs in people who are vegetarian and don't take vitamin supplement, also malabsorption could lead to B12 def, also there is a condition called pernicious anemia which is an autoimmune disease and these patient cannot absorb b12. .
B12 anemia. Usually it is due to decreased absorption by the stomach due to multiple reasons. Decreased acid in the stomach perhaps due to acid suppressing drugs, alcohol, vegetarians to name a few reasons.