most vitamins function as coenzymes
Important B vitamins that are used as large components of coenzymes include riboflavin, niacin, biotin, pantothenic acid, B6, folate and B12. For example riboflavin, or vitamin B2 is used as a large component of FAD and FADH, and niacin is an important component of NAD and NADH.
In this case the vitamins are called coenzyme vitamins. Some examples of coenzyme vitamins include Vitamin B1 in the form of thiamin diphosphate (or cocarboxylase) and Vitamin B6 in the form of pyridoxal 5â-phosphate. Coenzyme vitamins and direct precursors of coenzyme vitamins are found in foods in relatively small, but significant amounts.