Thiamine Requirement in the Adult Human as Measured by Urinary Excretion of Thiamine Metabolites

Abstract

Normal, healthy young men consumed a diet with a restricted intake of thiamine. Urinary excretion of thiamine, as well as the pyrimidine and thiazole moieties of thiamine, were measured. After 6 days of thiamine deprivation, the urinary thiamine excretion decreased to an average of 14 µg/24 hours. By the eighteenth day of deprivation, there was no detectable thiamine in the urine. Metabolite excretion increased during the depletion period and appeared to reach a constant level. It is proposed that this level of metabolite output represents a measure of the rate at which body stores of thiamine are being depleted. The maintenance of thiamine balance would require the amount that would replace the vitamin used for metabolic needs, and would represent the minimum daily requirement. The metabolite excretion from the eighteenth to the thirtieth day of depletion, when no thiamine was being excreted, averaged 903 µg/24 hours. However, the maximal amount excreted in any one day during this period was 913 µg/day. Two methods for calculating the thiamine requirement are possible: 1) subtracting the 160 µg of ingested thiamine from the metabolite output, leaving a net deficit of 753 µg of thiamine/day; this would make the minimum daily requirement 0.27 mg/1000 kcal; and 2) not subtracting the amount of ingested thiamine from the metabolite output, leaving a net deficit of 913 µg of thiamine/day. The minimum daily requirement would then be 0.33 mg/1000 kcal. Using a safety factor, the recommended daily allowance should be 0.54 to 0.66 mg/1000 kcal. This is in good agreement with previous work which correlated clinical symptoms with the available biochemical tests.