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Influence of Increasing Doses of Thiamine and Riboflavin on Efficiency of Their Utilization¹

Department of Agricultural Chemistry, University of Arkansas, Fayetteville

A quantitative metabolism study was made of the influence of increasing doses of thiamine and riboflavin on their efficiency of utilization. The daily doses used were: 5, 10, 20, 50, 100, and 1,000 µg. For thiamine, the 5-, 10-, 20-, and 50-µg. doses were most efficiently utilized. On higher levels of intake the efficiency of utilization decreases, there being a marked drop on the 1,000-µg. daily dose. The efficiency of utilization on the 50-, 100-, and 1,000-µg. daily doses were 92.1, 82.9, and 51.9%, respectively.

It is impossible at present to evaluate the efficiency of utilization of the 5-, 10-, and 20-µg. doses of riboflavin, because the fecal excretions indicate some bacterial synthesis. However, on the higher intakes of 50-, 100-, and 1,000-µg. doses, the total fecal riboflavin excretions are insignificant in terms of the total intake of this vitamin, hence the figures of 76 to 88% utilization on these higher doses are significant, and show that massive doses of riboflavin are much more economically utilized than equal intakes of thiamine. The total thiamine and riboflavin excretions do not account for the total intake of these vitamins. Neither could they be accounted for by storage in the animal tissues. However, incubation at 37° C. for 22 to 48 hours showed appreciable destruction of thiamine and riboflavin by liver, lung, heart, stomach, small and large intestines. It would appear then that part of the losses of thiamine and riboflavin in metabolism are caused by their destruction in the tissues.

Manuscript received 18 June 1943.