Vitamin, individual niacin

The ULs for vitamin E, niacin, and folate apply to synthetic forms obtained from supplements, fortified foods, or a combination of the two P-Carotene supplements are advised only to serve as a provitamin A source for individuals at risk of vitamin A deficiency... 

Generally, AA is determined individually, and only about a 10% of the published methods determine AA simultaneously with other analytes such as uric acid, glucose, fructose, dopamine, iodate, bromate, hypochlorite, thiourea, glutathione, hydrogen peroxide, acetylsalicylic acid, kojic acid, ascorbyl glucoside, paracetamol, cysteine, and other water soluble vitamins (thiamine [vitamin Bj], folic acid [vitamin B12], niacin [vitamin B3], riboflavin [vitamin B2], and pyridoxine [vitamin B ]). 

The water-soluble vitamins comprise the B complex and vitamin C and function as enzyme cofactors. Fofic acid acts as a carrier of one-carbon units. Deficiency of a single vitamin of the B complex is rare, since poor diets are most often associated with multiple deficiency states. Nevertheless, specific syndromes are characteristic of deficiencies of individual vitamins, eg, beriberi (thiamin) cheilosis, glossitis, seborrhea (riboflavin) pellagra (niacin) peripheral neuritis (pyridoxine) megaloblastic anemia, methyhnalonic aciduria, and pernicious anemia (vitamin Bjj) and megaloblastic anemia (folic acid). Vitamin C deficiency leads to scurvy. 

In an investigation of the water-soluble vitamins in human skin,71 it was found that 15 individuals showed relatively small ranges (less than 2-fold) for vitamin B12, folic acid, and biotin about 2-fold ranges in the cases of riboflavin, niacin, and thiamine about a 4-fold range in the case of ascorbic acid, and more than a 5-fold range in the case of pantothenic acid. In another study72 it was found that the total choline content of normal skin varied in four individuals over approximately a 10-fold range 127 to 1200 ig. per gm. The variation in the free choline in the same individuals was relatively small. 

Although microbiological methods are widely used for quantitation of total niacin, they tend to be time consuming and labor intensive (100). Reproducibility problems have also been reported (96). The HPLC methods for foods generally determine total niacin rather than the individual vitamers. Table 14 summarizes a recent HPLC method for quantitating total niacin in foods. The simultaneous determination of niacin with one or more other B vitamins is covered later in this chapter in Sec. XI. 

Besides these studies with individual vitamins, there are studies with rats that had received none of the vitamins of the B group (Morgan and Yudkin, 1957). With 20% sorbitol in the diet, the animals grew well for the 13 weeks of the experiment. The diets were such that they would not produce deficiences of vitamin B12, biotin, or niacin however, we can conclude that sorbitol can spare simultaneously at least thiamine, riboflavin, pantothenic acid, pyridoxine and folic acid. 

The individual vitamin demand varies widely and is also dependent on the personal constitution. Stressful situations and e.g. pregnancy require a higher vitamin intake. For men, the recommended daily dose of Vitamin A, Bj, B2, Bg, K and niacin is usually higher than for women. There are series of studies, which confirm the breadth of application and the tolerability of vitamins and other micronutrients. The pharmacological effects with high doses of antioxidant provitamins and vitamins (especially )S-carotene and Vitamins C and E) in the treatment of cardiovascular and other diseases have been encouraging, albeit further controlled clinical studies will be needed to substantiate these observations. 

Sources Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Huoride (1997) Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin 85, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline (1998) EHetary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (2000) Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001) Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005) and EHetary Reference Intakes for Calcium and Vitamin D (2011). These reports may be accessed via www.nap.edu A Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Unless otherwise specified, the UL represents total intake from food, water, and supplements. Due to a lack of suitable data, ULs could not be established for vitamin K, thiamin, riboflavin, vitamin B12, pantothenic acid, biotin, and carotenoids. In the absence of a UL, extra caution may be warranted in consuming levels above recommended intakes. Members of the general population should be advised not to routinely exceed the UL. The UL is not meant to ply to individuals who are treated with the nutrient under medical supervision or to individuals with predisposing conditions that modify their sensitivity to the nutrient... 

The electron density map of pyridine (see IOC) clearly shows a high concentration of electron density (more red) on the nitrogen. Note that pyridine has been implicated in male sterility, although some claim this is a myth. Nonetheless, it is reasonable to exercise caution when pyridine is used. Several important pyridine derivatives have substituents on the aromatic ring, including 2,6-lutidine (11) and picolinic acid (12). Many derivatives of pyridine are found in pharmaceutically active compounds. One is nicotinic acid (niacin, 13), which is vitamin Bg and is found in liver, yeast, and meat. A deficiency in this vitamin can lead to pellagra (a wasting disease). Nicotinamide (14, niacinamide) is one of the two principal forms of the B-complex vitamin niacin. Nicotinamide may be useful for individuals with type 1 (insulin-dependent) diabetes. 

Water soluble vitamins are generally not stored in the body, or are stored only for a limited time and the excess is excreted in the urine. Lipophilic vitamins are stored mainly in the Hver. The reserve capacity, defined as the time during which the need for the vitamin is covered by the organism reserves, is the longest for corrinoids (3-5 years) and vitamin A (1-2 years). The reserve capacity for folacin is 3-4 months, for vitamins C, D, E and K, riboflavin, pyridoxine and niacin it is 2-6 weeks, and for thiamine, pantothenic acid and biotin it is only 4-10 days. Reserve capacity is affected by the history of vitamin intake, the metabolic need for the vitamin and the health status of the individual. 

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. 

Only a few ducklings are able to survive at the low level of 50 mg/100 gm diet of tryptophan, whereas all survive at a supplement of 1 gm/100 gm diet. Although the results are still preliminary, they suggest that there may be a genetic factor in the ability of animals to utilize tryptophan as a growth factor in the absence of niacin. It is possible that the difference in response of the individual birds may be due to a quantitative or qualitative difference in the enzymes involved in the formation of niacin from tryptophan. The individuals, growing in the absence of either added nicotinamide or tryptophan, may have an enzyme complement particularly efficient in promoting the synthesis of the vitamin from tryptophan. 

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