The Biosynthesis of Riboflavin in Man

It is clearly established that micro-organisms present in the rumen of ruminant animals will synthesize riboflavin in quantities sufficient to supply the requirements for this factor.1Biosynthesis of riboflavin has also been demonstrated in the cecum of the rat,2but in this omnivorous animal the phenomenon is conditioned by the diet, and only under particular conditions is it sufficient to furnish the requirements. Although it seems reasonably clear that riboflavin deficiency does occur in man, it is by no means clear that it always develops whenever the diet is deficient in riboflavin. The possibility that under given dietary conditions the intestinal bacteria of man might synthesize riboflavin, providing protection against deficiency, has never been evaluated. It is our purpose in the present report to describe experiments which demonstrate clearly the biosynthesis of riboflavin in the human intestinal tract— and in considerable quantities. EXPERIMENTAL Observations were made on 12