Deficiencies, nutritional niacin

Under certain nutritional conditions, e.g. when maize forms the bulk of the human diet, the deficiency of niacin leads to pellagra. Treatment of maize with lime, as practised by Central Americans, releases niacin precursors. Pellagra is therefore not common among them, in spite of their monotonous diet, but was common among poor Europeans who did... 

Nutritionally, humans derive their pyridoxal coenzyme from vitamin B6. Most symptoms of vitamin Be deficiency apparently result from the involvement of the coenzyme in the biosynthesis of neurotransmitters and the niacin group of NAD and NADPH rather than from amino acid deficiency. 

After it had been established that pellagra was a nutritional deficiency disease, the next problem was to discover the missing nutrient. Additional dietary protein was shown to be beneficial, thus it was concluded that pellagra was because of a protein deficiency. This view, and later that it was more specifically from a deficiency of tryptophan, was held for some time. In 1938, Spies and coworkers showed that nicotinic acid would cure pellagra thereafter it was gradually accepted that it was a niacin deficiency disease. 

Erythrocyte NAD falls during niacin depletion and rises during repletion in human subjects. Erythrocyte NADP is unaffected, and the ratio of NADiNADP provides a useful index of niacin nutritional stams, with a ratio <1.0 indicating deficiency (Fu et al., 1989). 

The most widely used method for assessing niacin nutritional status is measurement of the urinary excretion of niacin metabolites. Table 8.1 shows the excretion of A( -methyl nicotinamide and methyl pyridone carboxamide in niacin adequacy and deficiency. 

Oduho GW, Han Y, and Baker DH (1994) Iron deficiency reduces the efficacy of tryptophan as a niacin precursor. Journal of Nutrition 124,444-50. 

The excretion of methyl pyridone carboxamide is more severely reduced in marginal niacin deficiency than is that of -methyl nicotinamide. The excretion of methyl pyridone carboxamide decreases rapidly in subjects fed on a niacin-deficient diet, and virtually ceases several weeks before the appearance of clinical signs of deficiency by contrast, a number of studies have shown continuing excretion of -methyl nicotinamide even in pellagrins. A better estimate of niacin nutritional status can be obtained by determining the ratio of urinary methyl pyridone carboxamide Ai -methyl nicotinamide, which is relatively constant, despite the administration of loading doses of tryptophan or niacin to adequately nourished subjects (between 1.3 to 4.0), and a ratio of less than 1.0 indicates depletion of niacin reserves (de Eange and Joubert, 1964 Dillon et al., 1992). 

Animals and yeasts can synthesize nicotinamide from tryptophan via hydroxyanthranilic acid (52) and quinolinic acid (53, Fig. 6A) (31), but the biosynthetic capacity of humans is limited. On a diet that is low in tryptophan, the combined contributions of endogenous synthesis and nutritional supply of precursors, such as nicotinic acid, nicotinamide, and nicotinamide riboside, may be insufficient, which results in cutaneous manifestation of niacin deficiency under the clinical picture of pellagra. Exogenous supply of nicotinamide riboside was shown to promote NAD+-dependent Sir2-function and to extend life-span in yeast without calorie restriction (32). 

The nutritional history of niacin is unusually colorful and involves Italy, Mexico, and the American South. The documentation of niacin deficiency seems to have started a long time ago, when com was brought to Spain by Columbus, Com is distinguished as being iow in niacin. The introduction of corn to Europe resulted in its widespread cultivation it replaced rye as a major crop. Com became popular... 

Niacin is a nutritional supplement used during periods of deficiency known as pellagra and for the treatment of dyslipidemia. Niacin needs may increase during chronic illness such as diabetes mellitus, malignancy, metabolic diseases, hyperthyroidism, infections, chronic fever, alcoholism, and during pregnancy and lactation. 

Nicotinamide-adenine dinucleotide (NAD diphosphopyri-dine nucleotide) and nicotinamide-adenine dinucleotide phosphate (NADP also termed triphosphopyridine nucleotide) represent most of the niacin activity found in good sources that include yeast, lean meats, liver, and poultry. Milk, canned salmon, and several leafy green vegetables contribute lesser amounts but are still sufficient to prevent deficiency. Additionally, some plant foodstuffs, especially cereals such as corn and wheat, contain niacin bound to various peptides and sugars in forms nutritionally not readily available (niacinogens or niacytin). Because tryptophan is a precursor of niacin, protein provides a considerable portion of niacin equivalent. As much as two thirds of niacin required by adults can be derived from tryptophan metaboHsm via nicotinic acid ribonucleotide... 

The history of niacin revolved around trying to find a way to prevent and cure pellegra, the late-stage deficiency disease caused by a niacin deficiency. Pellagra has been a serious nutritional disorder in the United States, mostly in the southeast. Two thousand deaths from pellagra were reported in 1941. This is ironic because nicotinic acid, later knovm as niacin, was first reported during the structure elucidation of the alkaloid nicotine. 

Niacin is found in fish, lean nneat, legunres, milk, and whole-grain and enriched cereals. The RDA for niacin is 20 mg per day. Niacin deficiency leads to dermatitis, diarrhea, dementia, and death. The most common illness that develops from niacin deficiency is pellagra, a form of dermatitis. This nutritional disease is found where corn is abundant in the diet and meat is scarce. 

Sources. Niacin and substances that are convertible to niacin are found naturally in meat (especially red meat), poultry, fish, legumes, and yeast. In addition to preformed niacin, some L-tryptophan found in the proteins of these foods is metabolized to niacin. Niacin is also present in cereal grains, such as corn and wheat. However, consumption of corn-rich diets has resulted in niacin deficiency in certain populations. The reason for this is that niacin exists in cereal grains in bound forms, such as the glycoside niacytin, which exhibit little or no nutritional availability. Interestingly, niacin deficiency is not common in Mexico and Central America even though the diets of those in these countries are based on com. Alkaline treatment, such as soaking corn in a lime solution—the process used by the populations of Mexico and Central America in the production of com tortillas—yields release of bound niacin and increased availability of the vitamin. 

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