Intestinal Absorption of Thiamin in Man Compared with Folate and Pyridoxal and Its Subsequent Urinary Excretion

Abstract

The intestinal absorption of thiamin was compared with that of folate and pyridoxal in six healthy volunteers using an oral dose of each vitamin equivalent to ten times the recommended daily allowance. Folate and pyridoxal were rapidly absorbed and following the oral dose, serum concentrations rose from a mean basal level of 10.9/mg/liter and17.5mg/liter to 174.8 mg/liter and 315.2 /mg/liter respectively -an increases of 1,500% for folate and 1,701% for pyridoxal. The mean serum level of thiamin rose only marginally from 5.1 /ig/liter to 7.2 /mg/liter, an increase of 42%. One hour following the oral test dose of thiamin, the vitamin was actively excreted in the urine of all volunteers, with a mean creatinine/thiamin renal clearance ratio of 2.4. Active excretion continued for up to six hours. In contrast, folate was only actively cleared for a short period in two volunteers. Thiamin absorption appeared to be controlled and limited, and modest increases in the serum concentration were accompanied by active renal clearance. © 1984, Center for Academic Publications Japan. All rights reserved.