Niacin Requirements and Reference Intakes

methyl pyridone carboxamide A/ -methyl nicotinamide  

Sources From data reported by de Lange and Joubert, 1964 Kelsay, 1969 Gontzea  

In view of the central role of the nicotinamide nucleotides in energy-yielding metabolism, and the fact that, at least in theory, the nicotinamide released by ADP-ribosyltransferase (Section 8.4.2) and poly(ADP-ribose) polymerase (Section 8.4.3) is available to be reutilized for nucleotide synthesis (although this may not occur when these enzymes are significantly activated), niacin requirements are conventionally calculated on the basis of energy expenditure. 

The depletion/repletion studies of Horwitt et al. (1956) and others have suggested, on the basis of restoration of urinary excretion of -methyl nicotinamide, that the average niacin requirement is 5.5 mg per 1,000 kcal (1.3 mg per MJ). Allowing for individual variation, reference intakes (see Table 8.2) are set at 6.6 mg niacin equivalents (preformed niacin - -1 /60 of the dietary tryptophan) per 1,000 kcal (1.6 mgper MJ). Even when energy intakes are very low, it must be assumed that energy expenditure will not fall below 2,000 kcal, and this is the basis for the calculation of reference intakes for subjects with low energy intakes. 

There is probably little or no requirement for any preformed niacin in the diet, because it is likely that average intakes of protein (at least in developed countries) wUl provide enough tryptophan to meet requirements (Section 8.3). Assuming that the average diet provides some 15% of energy from protein, and this protein meets the reference pattern for essential amino acids and provides 14 g of tryptophan per kg of dietary protein, this implies an intake of 

The depletion/repletion studies of Horwitt et al. (1956) emd others have suggested, on the basis of restoration of uiineuy excretion of -methyl nicoti- 

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On the basis of depletion/repletion studies in which the urinary excretion of niacin metabolites was measured after feeding tryptophan or preformed niacin, the average requirement for niacin is 1.3 mg niacin equivalents per MJ energy expenditure, and reference intakes are based on 1.6 mg/MJ. 

There are numerous sources of niacin that are essential and these include poultry, fish (tuna, salmon), meat (beef), yeast, legumes, milk and fortified eereals. In addition, niacin is naturally occurring in tiny amounts and the human body can make nicotinic acid from the metabolism of dietary tryptophan (Vosper 2009). The body requires tryptophan for two main reasons (i) for the synthesis of niacin and (ii) to raise serotonin levels, which is essential for the regulation of sleep, appetite and mood. The vast majority of proteins contain about 1 % of tryptophan and it is suggested that approximately 100 g of protein intake a day will be sufficient to ensure optimum levels of niacin in the body. The recommended dose of niacin is higher when there is an increase in physiological states such as pregnancy and lactation. Importantly, the Committee of Medical Aspects of Food Policy (COMA) in the UK stated that the Reference Nutrient Intake (RNI) for niacin was 17 mg/day and 13 mg/day. 

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