Thiamine also urinary excretion

Determination of the urinary excretion of thiamine in a 4-hour specimen, especially with comparison of excretion before and after a test load, is helpful in differentiating among extremes of thiamine status. However, as with most assessments based on amount of water-soluble vitamins in urine, excretion can be influenced considerably by dietary intake, absorption, and other factors. Measurements of certain urinary metabolites, notably thiamine acetic acid, have also been suggested as reflecting thiamine status. ... 

Sorbitol also leads to an increase in the urinary excretion of thiamine (Haenel et al., 1959 Hollmann et al., 1959). As with the increase of thiamine in the tissues, this suggests very strongly that at least some of the increased thiamine found in the alimentary canal becomes available to the rat. 

Nutritional status assessment for thiamine is generally carried out by assaying the total thiamine in whole blood or erythrocytes, or by measuring the activity of erythrocyte transketolase before and after incubation with exogenous thiamine pyrophosphate. The latter serves as the sensitive index of thiamine nutritional status (Brin 1980). In addition to the enzymatic test, a measure of urinary thiamine in relation to dietary intake has been the basis for balance studies to assess the adequacy of intake. When thiamine excretion is low, a larger portion of the test dose is retained, indicating a tissue s need for thiamine. A high excretion indicates tissue saturation. In the deficient state, excretion drops to zero. Plasma pyruvate and lactate concentrations have also been used to assess thiamine status. 

Human beings seem to become adapted to low intakes of thiamine, under favorable conditions. Requirements are increased in conditions that involve increased metabolism such as exercise, fever, and hyperthyroidism. The health and motility of the intestinal tract is also a factor. Needs are increased only up to a plateau, since urinary excretion tends to keep pace with consumption, even from low levels. It is thus not clear how the ingestion daily of thiamine in excess of apparent needs is literally a margin of safety against a future stress. Very high dosages for short times have produced no toxic symptoms, but protracted use of thiamine without other B vitamins may produce undesirable effects. 

Ascorbic acid is one of the most easily destroyed of vitamins, by heat and air. Destruction also seems to occur in the intestinal tract. As with thiamine and some other vitamins, the urinary excretion of ascorbic acid increases as the dietary intake increases so that there must be a point at which it is no longer economically sound to add it to the diet. Synthesis of ascorbic acid takes place in the bodies of most species man, monkeys, and guinea pigs need a dietary source. 

Chronic alcoholism may also precipitate beriberi since alcohol cannot be converted to fat in the body, but must be metabolized by the same thiamin- dependent processes as carbohydrate and protein. Furthermore, alcohol increases urinary excretion of water (diuretic effect) and water-soluble vitamins. A similar, but lesser, effect may result from the heavy consumption of caffeine (in beverages such as coffee, colas, and tea) coupled with a diet chronically high in refined foods which are rich in carbohydrates. (Like alcohol, caffeine is a diuretic. Also, it stimulates the utilization of stored carbohydrate for energy.)... 

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