Vitamin B is not just one vitamin, but instead it is a complex of eight different important vitamins. The mix includes vitamins B1, B3, B5, B6, B7, B9 and B12. Each one of the B vitamins has an essential function in the body and is necessary for maintaining overall health. Together, the complex supports the immune and nervous systems, metabolism, skin and muscles. The B vitamins are essential to enzymes that regulate chemical reactions in the body.