Nutrient requirements Niacin

Also see ADDITIVES CEREAL GRAINS, section headed "Enriched or Fortified Cereals" CORN, Table C-23 Com Products and Uses for Human Food FLOURS, section headed "Enrichment and Fortification of Flours" IRON, section headed "Sources of Iron" NIACIN, section headed "Sources of Niacin" NUTRIENTS REQUIREMENTS, ALLOWANCES. FUNCTIONS, SOURCES RIBOFLAVIN, section headed "Sources of Riboflavin" RICE, section headed "Nutritional Value" THIAMIN, section headed "Sources of Thiamin" and WHEAT, section headed "Enriched Flour.")... 

Nicotinate and nicotinamide, together referred to as niacin, are required for biosynthesis of the coenzymes nicotinamide adenine dinucleotide (NAD"") and nicotinamide adenine dinucleotide phosphate (NADP" ). These both serve in energy and nutrient metabolism as carriers of hydride ions (see pp. 32, 104). The animal organism is able to convert tryptophan into nicotinate, but only with a poor yield. Vitamin deficiency therefore only occurs when nicotinate, nicotinamide, and tryptophan are all simultaneously are lacking in the diet. It manifests in the form of skin damage (pellagra), digestive disturbances, and depression. 

On the other hand, milk is not only an essential food for infants, but for children and adults as well. Children need sufficient nutrients and energy to meet the demands of growth and development. Demands for nutrients such as protein, Ca, Fe, and Zn are relatively high, and teenagers require quite large amounts of B vitamins - thiamine, riboflavin and niacin. In addition, approximately 45 percent of the adult skeleton is laid down during adolescence. 

Several compounds, e.g., vitamin D and niacin, are apparently required in the diet even though pathways for their synthesis occur in the body. Such a situation may arise if a pathway does not provide an adequate supply for the body s needs or if the material cannot be readily transported from the site of synthesis to the place of action. The compounds discussed below are essential dietary nutrients in one or more nonhuman species, but such a status in humans is not supported by evidence. 

The Federal Enrichment Act of 1942 required the millers of flour to restore iron, niacin, thiamin and riboflavin lost in the milling process. Enriched flours and baked goods made from them are now excellent sources of niacin. Niacin may also be found in meat, poultry, fish, whole grains, and peanut butter. Besides direct niacin intake, humans can convert the amino acid tryptophan to niacin. Many people take daily vitamin supplements to ensure they get enough niacin and other essential nutrients, see also Coenzyme Nicotinamide Adenine Dinucleotide. 

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. 

In dogs, the niacin requirement appears to be about ten times that of thiamine.In rats, niacin is an essential nutrient only when the tryptophan content of the diet is low, and under these circumstances requirement is about ten times the thiamine need. The recommended dietary allowances for niacin in this country are ten times the thiamine allowances (Table 1). In view of the above data, these allowances should provide a fair margin of safety. 

MINERAL AND VITAMIN SUPPLEMENTS. There is considerable controversy among nutritionists and pediatricians regarding the amounts and types of nutrient supplements that are required by infants, since breast-fed infants have long been given little or no supplementation. Furthermore, the need for supplementation depends upon a variety of factors such as (1) status of the infant at birth, since preterm or low birth weight infants have higher nutritional requirements to attain the rates of growth and development of normal infants (2) type of milk or formula used (3) affliction of the infant with diarrhea, fever, infection, and/or other stresses and (4) age at which supplemental foods are introduced. It is noteworthy that even breast milk is low in iron, copper, fluoride, vitamins A, D, and E, and biotin, folacin, niacin, thiamin, and vitamin B-6. Furthermore, diluted evaporated milk is notably inferior to breast milk with respect to the contents of iron, zinc, vitamin A, vitamin E, and vitamin C. Therefore, the need for nutrient supplements should be evaluated by a health professional who is familiar with the diet and the overall health status of the infant. 

Niacin is well absorbed, even when gastrointestinal disorders are present. Often, a pellagra victim suffers from multiple vitamin and nutrient deficiencies, and, therefore, may require supplemental sources of the vitamin B complex and protein. Brewers yeast has often been used as such a supplement. 

Vitamins, minerals, and electrolytes— Studies have shown that during moderate to severe stresses, more zinc, copper, magnesium, and calcium are lost in the urine. Furthermore, stress results in altered blood levels of vitamins A and C, and of zinc and iron. Also, part of the response to stress includes water and sodium retention, via veisopressin and aldosterone secretion. As for the water-soluble vitamins—thiamin, riboflavin, niacin, pyridoxine (B-6), pantothenic acid, folic acid, and vitamin C stress increases their requirement. However, no dietary recommendations are made for these nutrients for individuals under stressful situations. Still, it seems wise to supply some supplementation before deficiency symptoms appear. 

FUNCTIONS. In the human body, vitamin B-12 is converted to a coenzyme form, if it is not already in such form. There are two active coenzyme forms Coenzyme B-12 (ade-nosylcobalamin), and methyl B-12 (methylcobalamin). Coenzyme B-12 has an adenosine ribonucleoside attached to the cobalt atom in the vitamin B-12 molecule in place of the cyanide group, whereas methyl B-12 contains a methyl group in place of the cyanide group. The conversion of vitamin B-12 to coenzyme forms requires many nutrients, including riboflavin, niacin, and magnesium. 

On that basis the average British diet does meet all requirements since, according to the National Food Survey, the nutrients available on a family basis from foods purchased are greatly in excess of RDI (except for iron, which approximates to RDI). The lowest of these values is about 130 % RDI for thiamin and riboflavin, and near 200 % for protein, calcium, niacin equivalents and vitamin A. 

The conversion of tryptophan to nicotinic acid in vivo is depicted in Figure 1. The rate of conversion of tryptophan to niacin and the pyridine nucleotides is controlled by the activities of tryptophan dioxygenase (known alternatively as tryptophan pyrrolase), kynurenine hydroxylase, and kynureninase. These enzymes are, in turn, dependent on factors such as other B vitamins, glucagon, glucocorticoid hormones, and estrogen metabolites, and there are various competing pathways which also affect the rate of conversion. For these reasons, a variety of nutrient deficiencies, toxins, genetic and metabolic abnormalities, etc. can influence niacin status and requirements. 

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