Metabolism of Thiamine
McCarthy and others injected thiamine-S into normal rats and recovered about 65 per cent of the injected activity in the urine collected during ten days following administration. Thiamine-deficient rats excreted 52 per cent of the original radioactive sulfur in the time period. In each case most of the radioactive sulfur appeared in the neutral sulfur fraction and a small amount as sulfate.
Thiamine Requirement
One USP unit of thiamine is equal to Ilg of thiamine hydrochloride. This is identical to the lU Because of the well-established relationship of thiamine to carbohydrate metabolism, the requirement of this vitamin for man is most accurately predicted on the basis of the caloric intake and primarily the carbohydrate intake. This, however, is not the most practical approach from a nutritional standpoint. Since individual diets vflIY to such a great extent and because of other individual variations, exact figures for human thiamine requirement are not highly significant.
The general trend in the past few years has been to revise downward the estimated daily thiamine need. Thus the recommended dietary allowance adopted by the Food and Nutrition Board of the National Research Council was revised from 0.6 mg to 0.5 mg per 1000 Cal in 1953 and remained essentially the same in the 1958 revision. A further downward revision to 0.4 mg per 1000 Cal per day was adopted in the 1963 revision. For a 3000 Cal diet the daily thiamine requirement would be approximately 1.2mg. Such allowances are not to be confused with requirements.
The allowances were designed to allow a fair margin above actual requirements. Still lower -intakes are apparently able to cover the needs. In a recent study the thiamine requirement of adults was calculated to be 0.27 to 0.33 mg per 1000 Cal of diet per day. The recommended daily allowance then would be twice this, or 0.54 to 0.66 mg per 1000 Cal per day. The use of massive doses of thiamine for various clinical entities, such as nausea of pregnancy and "nervousness," seems to be successful only in isolated cases.
