The conversion of tryptophan (Trp) → nicotinamide (Nam) is an important pathway for supplying vitamin niacin. We reported the following two phenomena: (1) severe food restriction led to an increase in the Trp → Nam conversion compared with free-access control group; (2) the conversion of Trp → Nam is also increased by vitamin B1 deficiency compared with free-access control group. The present study was done to clarify whether or not a true reason about an increase in the Trp → Nam conversion is a vitamin B1 deficiency or severe food restriction. The present results showed that vitamin B1 deficiency suppressed the increased conversion of Trp → Nam induced by severe food restriction, probably by suppressing 3-hydroxyanthranilic acid 3,4-dioxygenase protein synthesis in liver.
