p> - niacin is essential for the metabolism of carbohydrate, fat and protein. It is also essential for the normal functioning of skin , intestinal and nervous system. - it differs from other other B complex vitamins that an essential amino acid tryptophan serves as its precursor. - about 60 mg of tryptophan is required to result in 1 mg of niacin Reference : Park's textbook of preventive and social medicine, 23rd edition, pg no:619