The function of vitamin B is a difficult topic. B9 (folic acid) and B12 (cobalamin) are necessary for the function of the methylation cycle (for detoxification). The problem is that a lot of people have methylation defects and cannot convert B9 and B12 to their active methyl forms. If you take folic acid, while you have a certain methylation mutation, it can work counterproductive. I guess most people will do well on a B supplement. Vitamin B7 (biotin) is supposed to fight the reproduction of candida.
Vitamin B is water soluable which means that it is almost impossible to do harm with it.