Synthesis of B vitamins by intestinal bacteria

A considerable amount of biotin is synthesized by human intestinal bacteria, as evidenced by the fact that 3 to 6 times more biotin is excreted in the urine and feces than is ingested. But synthesis in the gut may occur too late in the intestinal passage to be absorbed well and play much of a direct role as a biotin source. Also, several variables affect the microbial synthesis in the intestines, including the carbohydrate source of the diet (starch, glucose, sucrose, etc.), the presence of other B vitamins, and the presence or absence of antimicrobial drugs and antibiotics. 

A completely independent study implicating the intestinal bacteria was that of Theiler and his associates (13) in ruminant animals. In the attempt to reproduce experimentally a South African paralytic disease known as lamzietke they fed cattle an experimental diet deficient in vitamin B and noted that evidences of deficiency failed to develop although pigeons on the same diet developed polyneuritis promptly. They assumed that either the vitamin requirement of cattle was extremely low or that it had been satisfied by bacterial synthesis in the intestinal tract the latter explanation seemed the more probable. 

The phenomenon of vitamin synthesis by bacteria presents important considerations in the nutrition of man. Its full significance, however, should await a more complete knowledge of the human need for the B vitamins than we now possess. At the present time, we are certain that at least part of our requirements are furnished by bacterial action in the intestines. It is, therefore, comforting to know that we can at least rely to some extent on this mechanism to supplement the average American diet should the ever persistent vitamin vendor fail in his benevolent task. 

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