B12 is the only one that is commonly talked about needing to be supplemented as a vegan; though in Australia if you consume Soy milk, you likely already get eno

B12 is the only one that is commonly talked about needing to be supplemented as a vegan; though in Australia if you consume Soy milk, you likely already get enough as it is fortified with it. B12 deficiency can have quite profound neurological effects, though thats in pretty severe cases, IIRC