Which of the following vitamin is synthesized in vivo, in the body by humans?
Niacin
Pantothenic acid
Cyanocobalamin
Folic acid
Ans: A. Niacin(Ref: Harper 30/e p547, 556)Niacin:Not strictly a vitamin.Can be synthesized in body from essential amino acid tryptophan.Two compounds, nicotinic acid & nicotinamide - Similar biologic activity of niacin.Metabolic function is as the nicotinamide ring of coenzymes NAD & NADP in oxidation-reduction reactions.