Following a request from the European Commission, the Panel on Dietetic Products, Nutrition and Allergies (NDA) derived Dietary Reference Values (DRVs) for niacin. Niacin is a generic term for nicotinic acid and nicotinamide. Niacin can be synthesised in the human body from the indispensable amino acid tryptophan. Approximately 60 mg of tryptophan yields 1 mg of niacin defined as 1 mg niacin equivalent (NE). Long-term inadequate intake of tryptophan and niacin can lead to the development of pellagra. In the absence of new scientific data, the Panel endorses the Average Requirement (AR) for adults of 1.3 mg NE/MJ (5.5 mg NE/1 000 kcal) adopted by the Scientific Committee for Food (1993), based on data on urinary excretion of niacin metabolites as an endpoint. The Population Reference Intake (PRI) of 1.6 mg NE/MJ (6.6 mg NE/1 000 kcal) is derived from the AR assuming a coefficient of variation of 10 %. For infants aged 7-11 months, children and adolescents, as well as for pregnant and lactating women, the Panel considers that there is no evidence that the relationship between niacin requirement and energy requirement differs from that of adults; therefore, the AR and PRI for adults are also applied to these age and life stage groups. Niacin is a generic term for nicotinic acid and nicotinamide, soluble organic compounds that belong to the group of B vitamins. Niacin is found in a wide range of foods. Main food groups contributing to niacin intakes of adults include meat and meat products, grains and grain-based products and milk and milk products. Depending on the foodstuff, the mean absorption of niacin is from about 23 % to about 70 %; it is lowest from cereals and highest from animal products. Niacin can be synthesised in the human body from the indispensable amino acid tryptophan. Approximately 60 mg of tryptophan yields 1 mg of niacin defined as 1 mg niacin equivalent (NE). Inadequate iron, riboflavin or vitamin B6 status decreases the conversion of tryptophan to niacin.In vivo nicotinic acid is converted to nicotinamide, which is a precursor for nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential to cells and involved in many biochemical reactions. Niacin circulates in the plasma as nicotinamide and nicotinic acid. Both forms are transported to cells and tissues, which they enter by diffusion to perform the intracellular functions of niacin. Niacin is trapped within the cell as NAD or NADP.The major pathway of catabolism of nicotinic acid and nicotinamide is by methylation in the liver to N-methyl-nicotinamide (NMN) and subsequent oxidation to N-methyl-2-pyridone-carboxamide (2-Pyr) and N-methyl-4-pyridone-carboxamide (4-Pyr). In humans, the two major excretion products are NMN and 2-Pyr, which under normal conditions represent about 20-35 % and 45-60 % of niacin metabolites, respectively. The amount of niacin metabolites excreted depends on the niacin and tryptophan intake. Long-term inadequate intake of tryptophan and niacin results in...