Thiamin dietary requirement

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. 

The dietary requirement for thiamine is proportional to the caloric intake of the diet and ranges from 1.0 - 1.5 mg/day for normal adults. If the carbohydrate content of the diet is excessive then an increased thiamine intake will be required. Requirement is increased in pregnancy and lactation. It also depends of intestinal s)mthesis and absorption and fat content of diet (increased Pyruvate). 

The water-soluble vitamins with hsted DVs are vitamin G, which is necessary for the prevention of scurvy (Section 4.3), and the B vitamins—niacin, pantothenic acid, vitamin Bg, riboflavin, thiamine, fohc acid, biotin, and vitamin Bj2. The B vitamins are the precursors of the metabohcally important coenzymes listed in Table 7.1, where references to the reactions in which the coenzymes play a role are given. We have seen many pathways in which NADH, NADPH, FAD, TPP, biotin, pyridoxal phosphate, and coenzyme A were found, all of which came from vitamins. A summary of vitamins and their metabolic roles is given in Table 24.2. Frequently, the actual biochemical role is played by a metabolite of the vitamin rather than by the vitamin itself, but this point does not affect the dietary requirement. 

Water-soluble vitamins are required by all beetles so far studied. As might be expected thiamine, riboflavin, niacin, pyridoxine, and pan-tothen were first detected as dietary requirements, and it may be concluded that these five are as important for the Coleoptera as for the Diptera and Ciliata. 

When considering sources of niacin, it should be noted that niacin can be, and is, synthesized by the intestinal flora. However, the amount produced is only of minor importance in the human. By contrast, as with thiamin and riboflavin, ruminants (cattle, sheep, etc.) have no dietary requirements for niacin because of bacterial synthesis in the rumen. 

Thiamin is required by all species of animals. They must have a dietary source, unless it is synthesized for them by microorganisms in the digestive tract, as in the case of ruminants. 

Vitamins are chemically unrelated organic compounds that cannot be synthesized by humans and, therefore, must must be supplied by the diet. Nine vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins (vitamins A, D, K, and E) are termed fat-soluble (Figure 28.1). Vitamins are required to perform specific cellular functions, for example, many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism. In contrast to the water-soluble vitamins, only one fat soluble vitamin (vitamin K) has a coenzyme function. These vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine, and significant quantities are stored in Die liver and adipose tissue. In fact, consumption of vitamins A and D in exoess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds. 

It was soon apparent that the new vitamin alone would not satisfy the dietary need of rats for the B factor. A second thermostable factor (B2) was required in addition to thiamin (B ), which was labile and easily destroyed by heating. When it became clear that factor B2 contained more than one component, it was called vitamin B complex. There was some confusion until relatively specific animal tests for each one of the members had been devised. 

TPP also mediates the oxidative decarboxylation of a-ketoglutaric acid, another intermediate of carboxydrate metabolism in the citric acid cycle. The nutritional requirement for thiamine increases as dietary carbohydrate increases because of a greater demand for TPP. 

An enzyme cofactor can be either an inorganic ion (usually a metal cation) or a small organic molecule called a coenzyme. In fact, the requirement of many enzymes for metal-ion cofactors is the main reason behind our dietary need for trace minerals. Iron, zinc, copper, manganese, molybdenum, cobalt, nickel, and selenium are all essential trace elements that function as enzyme cofactors. A large number of different organic molecules also serve as coenzymes. Often, although not always, the coenzyme is a vitamin. Thiamine (vitamin Bj), for example, is a coenzyme required in the metabolism of carbohydrates. 

The first water-soluble vitamin discovered was called vitamin B to distinguish it from vitamin A. Later other B vitamins were discovered and given names such as vitamin B2, B2, etc. Now the specific chemical names are used. In distinction to the fat-soluble vitamins, the water-soluble vitamins are not absorbed with fats and they are not stored in appreciable quantities in the body (with the possible exception of B12 and thiamin). Excesses of these vitamins are excreted rapidly in urine, requiring a constant dietary supply. 

Cornerstones of treatment are dietary restriction of branched-chain amino acids and high dose thiamine, the latter showing responsiveness in cases with mild and/or intermittent presentations. Acute episodes are life threatening and require aggressive treatment peritoneal dialysis may be necessary because renal clearance of the toxic metabolites is poor. ... 

The current revival of interest in the relationship between dietary carbohydrate and vitamin requirements stems from the observations that rats grow and thrive without thiamine if their food contains sorbitol (Morgan and Yudkin, 1957). The problem which was being investigated was one of metabolism, but the answer, as we shall see, has little if anything to do with this. 

Thiamine has lieen studied in more detail than any of the other vitamins. This is no doubt chiefly because signs of its deficiency occur sooner than those of other vitamins. Our own studies were initiated because we thought that changes in dietary carbohydrate might affect thiamine requirements by changes in the metabolic needs. 

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. 

Thiamine requirements must be related in any logical standard to the calorie requirements, but there is no general agreement on how much thiamine is needed per 1000 calories. Experimental evidence has given values ranging from a low of 0.13 mg. per 1000 calories (Holt, 1944) up to 0.44 mg. per 1000 calories (Alexander et al., 1946). The Canadian Dietary Standard uses 0.33 to 0.35 mg. per 1000 calories, and the U.S. Recommended Dietary Allowances uses 0.5 mg. per 1000 calories. 

Juvenile Beriberi. The feeding of extra protein without extra thiamin to protein-deficient children who are stunted in their growth may bring on beriberi because (1) growth resumes and the need for thiamin is increased, and (2) part of the dietary protein may be converted in the body to carbohydrates and/or other substances which require thiamin for their metabolism. 

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. 

Enrichment of flour (bread) and cereals, with thiamin, riboflavin, niacin, and iron (with calcium enrichment optional), which was initiated in 1941, has been of special significance in improving the dietary level in the United States. On the basis of the average per capita consumption of flour and bread in the United States, slightly more than 40% of the daily thiamin requirement is now supplied by these foods. 

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