THE SYNTHESIS OF VITAMINS BY INTESTINAL BACTERIA IN MAN AND THE EFFECT OF CELLULOSE

V. SYNTHESIS OF NIACIN

Abstract

A human adult being used as a test subject, an ordinary, meat and vegetable diets were given respectively and the urinary and fecal niacin was estimated and the difference of the vitamin ingested from those excreted was assumed to the vitamin synthesized by the intestinal bacteria. A switch from an ordinary to a meat diet resulted in a little increase in urinary niacin but in a reduction both in the fecal niacin and in the niacin synthesized. On the contrary, a switch from an ordinary to a vegetable diet resulted in a marked increase in the niacin content of the urine and stool as well as the niacin synthesized. When cellulose was added to either a meat diet or a vegetable one, a marked rise occurred in the niacin synthesized. Furthermore, the amount of MNA and MCP excreted in urine was determined besides niacin, and it was found that the former two altered roughly in parallel with the latter, the former two being always higher. After ingesting cellulose the urinary excretion of the metabolites rose markedly, indicating a ready absorbability of the vitamin from the intestine. Taking the metabolites into consideration, the amount of niacin synthesized by intestinal bacteria after ingesting cellulose amounted to as high as 55-58mg per day.