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The Effect of the Ingestion of High Levels of Riboflavin on the Amount in the Milk and Urine¹

Department of Biochemistry and Nutrition, Agricultural and Mechanical College of Texas, College Station

The oral administration of large amounts of riboflavin to goats and sheep increased the true riboflavin content of the milk by only about 26%. Measured by the fluorometric procedure the riboflavin values were for the milk approximately 5 times greater than the values obtained by the microbiological method and for the urine the fluorometric values were about 12 times higher. The riboflavin content of the milk as measured by the microbiological assay agreed well with the growth response of rats fed the milk as a source of riboflavin.

The microbiological and fluorometric values for the riboflavin content of the urine of rats were in good agreement even when massive doses of 10 or 20 mg of riboflavin were administered daily. The microbiological and fluorometric values were in good agreement for urine from humans that had been fed 20 mg of riboflavin per day.

Goats and sheep fed large amounts of riboflavin evidently form a fluorescent compound that is measured by the fluorometric procedure for riboflavin. The unidentified compound secreted into the milk and excreted by the renal pathway is not biologically active.

Manuscript received 23 June 1947.