Vitamin dietary requirement

Estigmene acrea dietary requirement, vitamin accumulated in tissues during development 41,43... 

The present (ca 1997) maximum safe level of vitamin for long-term feeding in most species is four to ten times the NRC dietary requirements. Short-term (<60 d), most species can tolerate 100 times their apparent dietary requirements (210). 

Example 1.—A classical problem of linear programming is the diet problem. Given minimal needs for vitamins, iron, calcium, phosphorous etc., which are present in known proportions in a variety of possible foods with given prices, it is desired to determine a diet from these foods that meets the minimal needs for the vitamins and other ingredients at the lowest cost. To illustrate with a simple example and hypothetical figures, denote three types of food by Flt F2, F3, and two types of dietary requirements, e.g., vitamins by A and B. The table... 

Camitine deficiency can occur particularly in the newborn—and especially in preterm infants—owing to inadequate biosynthesis or renal leakage. Losses can also occur in hemodialysis. This suggests a vitamin-fike dietary requirement for carnitine in some individuals. Symptoms of deficiency include hypoglycemia, which is a consequence of impaired fatty acid oxidation and hpid accumulation with muscular weakness. Treatment is by oral supplementation with carnitine. 

Two essential enzymatic reactions in humans require vitamin B12 (Figure 33-2). In one, methylcobalamin serves as an intermediate in the transfer of a methyl group from /V5-methyltetrahydrofolate to homocysteine, forming methionine (Figure 33-2A Figure 33-3, section 1). Without vitamin B12, conversion of the major dietary and storage folate, N5-... 

Vitamin confers biologic activity upon prothrombin and factors VII, IX, and X by participating in their postribosomal modification. Vitamin is a fat-soluble substance found primarily in leafy green vegetables. The dietary requirement is low, because the vitamin is additionally synthesized by bacteria that colonize the human intestine. Two natural forms exist vitamins Ki and K2. Vitamin K1 (phytonadione Figure 34-5) is found in food. Vitamin K2 (menaquinone) is found in human tissues and is synthesized by intestinal bacteria. 

Milk contains significant concentrations of fat-soluble vitamins (Table 3.5, Figure 3.4) and milk and dairy products make a significant contribution to the dietary requirements for these vitamins in Western countries. The actual form of the fat-soluble vitamins in milk appears to be uncertain and their concentration varies widely with breed of animal, feed and stage of lactation, e.g. the vitamin A activity of colostrum is c. 30 times higher than that of mature milk. 

The classical niacin deficiency disease is pellagra, which is characterized by symptoms including diarrhoea, dermatitis, dementia and eventually death. High-protein diets are rarely deficient in niacin since, in addition to the preformed vitamin, such diets supply sufficient tryptophan to meet dietary requirements. Large doses of niacin can cause the dilation of capillaries, resulting in a painful tingling sensation. 

Endogenous vitamin precursor 7-Dehydrocholesterol, an intermediate in cholesterol synthesis, is converted to cholecalciferol in the dermis and epidermis of humans exposed to sunlight. Preformed vitamin D is a dietary requirement only in individuals with limited exposure to sunlight. 

In addition to the above water-soluble vitamins, other compounds are present in milk, such as choline, myo-inositol, and para-aminoben-zoic acid, compounds for which there is no proof of a dietary requirement for humans (NAS 1980A). 

Carboxybiotin Carboxyphosphate The p carboxylation step 756. .. Box 14-D Tables Dietary Requirements for B Vitamins... 

In terms of human dietary requirements, much of the wheat for breadmaking in the United States is produced in selenium-adequate sections of the country. Bread is generally a good source of dietary selenium, Selenomethionine decomposes lipid peroxides and inhibits in vivo lipid peroxidation in tissues of vitamin-E-deficient chicks. Selenocysdne catalyzes the decomposition of organic hydroperoxides. Selenoproteins show a high degree of inhibition of lipid peroxidation in livers of sheep, chickens, and rats, Thus, some forms of selenium exhibit in vivo antioxidant behavior,... 

Pyndoxal phosphate is also a cofactor for transamination reactions, In these reactions, an amino group is transferred from an amino acid to an or-keto acid, thus founing a new amino acid and a new or-keto acid, Transamination reactions are important for the synthesis of amino acids from non-protein metabolites and for the degradation of amino acids for energy production. Since pyridoxal phosphate is intimately involved ill amino add metabolism, the dietary requirement for vitamin B6 increases as the protein content of the diet increases. 

The desugaring of cane juice concentrates the heat- and alkali-stable vitamins in the final molasses. Even after this accumulation, only myo-inositol may have reached the level of minimum dietary requirements.109 Niacin, pantothenic acid and riboflavin are also present in significant quantities109 the thiamine, pyridoxin, pantothenic acid, biotin and folic acid contents of molasses have been estimated by bioassay.110 111 The biotin content of Hawaiian and Cuban molasses was 2.1 and 1.7 gammas per gram, respectively.119 The antistiffness factor (closely related to stigmasterol) has been found in cane molasses.88 89 The distillery slop from the yeast fermentation of molasses is marketed as a vitamin concentrate this product also contains vitamins originating in the yeast. 

Ascorbic acid (vitamin C) is a water-soluble vitamin but is not part of the B group. It is a metabolic requirement for all species but is a dietary requirement only for those that lack the enzyme for its synthesis (primates, guinea pigs, certain birds, fish). Therefore, it is not required in poultry diets. It is involved in the formation and maintenance of intercellular tissues having collagen or related substances as basal constituents. 

Biochemistry is important in many fields of science in addition to medicine. For instance, biochemists investigate food by studying molecules such as vitamins, amino acids, fatty acids, various minerals, and water, all of which are dietary requirements for healthy nutrition. They also explain how these nutrients are absorbed by the body and what they do in the cells. For example, the question of how the body derives energy from dietary fats and oils involves a series of biochemical reactions explained by the biochemistry of the metabolic pathways. 

Vitamin D was originally classified as a vitamin because of its presumed dietary requirement. However because of the capability of in vivo production and its mechanism of action, l,25(OH)2D3 can now more properly be considered a hormone in the steroid family. 

Answer Dietary niacin is used to synthesize NAD+. Oxidations carried out by NAD+ are part of cyclic oxidation-reduction processes, with NAD+/NADH as an electron carrier. Because of this cycling, one molecule of NAD+ can oxidize many thousands of molecules of glucose, and thus the dietary requirement for the precursor vitamin (niacin) is relatively small. 

Gerster H (1997) Vitamin A functions, dietary requirements and safety in hnmans. International Journal of Vitamin and Nutrition Research 67,71-90. 

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