What are the general roles of vitamins in human body?

Vitamins are essential to life. Nutritionally, they form a cohesive group of organic compounds that are required in the diet in small amounts for the maintenance of normal health and metabolic integrity.

Many vitamins are the precursors of coenzymes involved in energy metabolism and protein or nucleic acid synthesis.

Besides being cofactors for enzymes some vitamins such as fat soluble vitamins A and D have been shown to exhibit hormone-like functions.

Thus, vitamin A and its metabolites retinaldehyde and retinoic acids are involved in the growth, differentiation and maintenance of epithelial tissues as well as for reproduction.

Several vitamins are essential for normal immune functions: fat soluble vitamins A and E and water soluble vitamins B12 and C.

In general vitamins roles are as follows:
*Antioxidants
*Gene transcription elements
*H+/e- donors/acceptors
*Hormones
*Coenzymes
What are the general roles of vitamins in human body?