water-soluble vitamin nutraceutical B vitamin B vitamins B-group vitamins B-group vitamin A role played by any of the group of eight water-soluble vitamins originally thought to be a single compound (vitamin B). The group comprises of vitamin B1, B2, B3, B5, B6, B7, B9, and B12 (Around 20 other compounds were once thought to be B vitamins but are no longer classified as such). B vitamins play important roles in cell metabolism. vitamin B