Thiamine requirement

Thiamine requirements vary and, with a lack of significant storage capabiHty, a constant intake is needed or deficiency can occur relatively quickly. Human recommended daily allowances (RDAs) in the United States ate based on calorie intake at the level of 0.50 mg/4184 kj (1000 kcal) for healthy individuals (Table 2). As Httle as 0.15—0.20 mg/4184 kJ will prevent deficiency signs but 0.35—0.40 mg/4184 kJ are requited to maintain near normal urinary excretion levels and associated enzyme activities. Pregnant and lactating women requite higher levels of supplementation. Other countries have set different recommended levels (1,37,38). 

Classic beri-beri, rarely seen in the United States and Europe, except in alcoholism (P4), is endemic in the Far East because of the prevalent diet of decorticated rice (F6). It occurs in two forms wet beri-beri, characterized by edema and cardiovascular symptoms (G6), and dry beri-beri with peripheral neuritis, paralysis, and atrophy of the muscles. Conditions which may predispose to deficiency by increasing thiamine requirements are pregnancy (see section 2.4), and lactation, hyperthyroidism, malignant disease, febrile conditions, increased muscular activity, high carbohydrate diets, and parenteral administration of glucose solutions. A constant supply of thiamine is required for optimal nutrition because storage in the liver and elsewhere is limited. Thiamine is synthesized by bacteria in the intestinal tract of various animals, but this is not a dependable source for man. 

Pett,55 Director of the Division of Nutrition, Department of National Health and Welfare of Canada, has on the basis of the "best data possible,.. . admittedly not entirely satisfactory," arrived at the following figures for the thiamine requirements of 15 individuals ... 

The isolation of 5-formyl-2-methylpyrimidine (62) and 5-amino-2-methylpyrimidine (63) from thiamin requiring mutants of Neurospora has led to a suggestion that these may be late intermediates in the biosynthesis of (45), a contention supported in part by the demonstration of conversion of the amino compound (63) to the hydroxymethylpyrimidine (45) by yeast cell-free extracts. 

The free base is unstable, and two derivatives of thiamin are commonly used in food enrichment and pharmaceutical preparations thiamin chloride hydrochloride (generally known simply as thiaminhydrochloride) and thiamin mononitrate. The mononitrate is less hygroscopic than the chloride hydrochloride and is the preferred form for food enrichment. There is considerable difficulty in interpreting much of the literature on thiamin requirements, because many authors quote mg of thiamin, without specifying whether it was as the free base, the chloride hydrochloride, or the equivalent amount of free base. Because the Mr of free thiamin is 266.4, and that of the chloride hydrochloride is 337.3, this confusion can result in errors of the order of 26%. 

It is apparent from the central role of thiamin in carhohydrate metaholism that the requirement will depend on carhohydrate intake to a considerable extent. In practice, requirements are calculated on the basis of total energy intake, assuming that the average diet provides 40% of energy from fat. For diets that are lower in fat, and hence higher in carbohydrate and protein, thiamin requirements will be somewhat higher. 

Blass JP and Gibson GE (1977) Abnormality of a thiamine-requiring enzyme in patients with Wernicke-Korsakoff syndrome. New England Journal of Medicine 297, 1367-70. 

The severity of the symptoms of thiamin deficiency has been associated with energy intake. The consumption of large doses of glucose has been foimd to induce an unusual rise in plasma pyruvate and lactate, as well as neurological symptoms, in thiamin deficient humans. Because of this association, the thiamin requirement is sometimes expressed on a per energy intake basis. 

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. 

The pathway as presented in Table I shows that it is linear for the first 10 steps with no branch points before the pivotal IMP is formed. However, a branch point does exist for the synthesis of the pyrimidine moiety (Bi-pyrimidine) of thiamine. Convincing evidence has been obtained to indicate that AIR also serves as a precursor to Bi-pyrimi-dine [27]. This explains the concomitant growth requirement for thiamine for most of the mutants blocked in any one of the first five enzymes [27-29]. A complication in regulatory control is thus introduced in that any attempt to control purine biosynthesis at the first five steps would have dire consequences on the formation of thiamine. This has indeed been found in the often-reported cases where inhibition of growth by adenine and its derivatives can be reversed by thiamine or its pyrimidine moiety [29-31]. The situation is more complicated in a special class of adenine-sensitive mutants where the sensitivity appears to be related to disturbances in folic acid metabolism [32]. Mutations in the AICAR formyltransferase complex (steps 9 and 10) also create a pleiotropic thiamine requirement which is not due to a deficiency in the synthesis of thiamine but rather to an unexplained phenotypic... 

Anderson, S.H., Vickery, C.A., and Nicol, A.D., 1986. Adult thiamine requirements and the continuing need to fortify processed cereals. Lancet. 2 85-89. 

A varied diet should provide an adequate level of thiamine to prevent deficiency. The thiamine requirement of an individual is influenced by age, energy and carbohydrate intake, and body mass. On the basis of considerable evidence, the Food and Nutrition Board of the US Institute of Medicine recommends thiamine intake at a level of 0.5mg/1000kcal (4184KJ) (National... 

Research Council 1989). Because there are some data indicating lower availability of thiamine in older people, it is recommended that they maintain an intake of Img/day even if they consume less than 2000 kcal (8368 KJ daily). Since thiamine requirements increase during pregnancy and lactation, an additional intake of 0.4mg/day is recommended during pregnancy and 0.5 mg/ day during lactation. 

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