Even in vegeterian, due to less vit b12, anemia occurs so called megaloblastic anemia. This anemia can also be seen in patient with less vit b9 so called folic acid deficiency. First make sure it’s vit b12 or b9 deficiency because treating people with folic acid in case of vit12 deficient can worsen the neurological symptoms more of the patient.
P.S. Both are used in DNA synthesis .