Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver a scientific opinion on Dietary Reference Values for the European population, including niacin.
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 reduced urinary excretion of niacin metabolites, and can lead to the development of pellagra. Based on experimental studies on niacin deficiency, it is recognised that niacin requirement is strongly dependent on energy intake. No signs of niacin deficiency were observed in subjects on diets containing at least approximately 1 mg NE/MJ (4.4 mg NE/1 000 kcal), while providing no less than 8.4 MJ/day (2 000 kcal/day). Diets providing at least 1.3 mg NE/MJ (5.5 mg NE/1 000 kcal) were sufficient to prevent depletion and maintain niacin body stores, as indicated by a sharp increase in urinary excretion of niacin metabolites above this intake.
The Panel notes that no new scientific data that would necessitate an amendment of the DRVs for niacin have become available since the publication of the Scientific Committee for Food (SCF) report in 1993. The Panel therefore endorses the relationship proposed by SCF (1993) between niacin requirement and energy requirement.
The Panel endorses the Average Requirement (AR) for adults (men and women) of 1.3 mg NE/MJ (about 5.5 mg NE/1 000 kcal) and the Population Reference Intake (PRI) of 1.6 mg NE/MJ (about 6.6 mg NE/1 000 kcal) adopted by SCF (1993) assuming a coefficient of variation of 10 %. The Panel considers that there is no evidence that the relationship between niacin requirement and energy requirement for infants aged 7-11 months, children and adolescents differs from that of adults. Therefore, the AR and PRI for adults are applied to these age groups as well. The Panel also considers that, in pregnant and lactating women, there is no evidence that the relationship between niacin requirement and energy requirement differs from that of other adults. Therefore, the AR and PRI for adults are applied to these life stage groups. Taking into account the reference energy intake, i.e. the AR for energy for various Physical Activity Levels (PAL values), the intake of NE/MJ is also expressed as mg NE/day. The Panel notes that, as for other nutrient reference values, DRVs for niacin are set under the assumption that intakes of other essential nutrients, particularly iron, riboflavin, vitamin B6 and protein, and energy are adequate.