Correlation of Urinary Excretion of Riboflavin with Dietary Intake and Symptoms of Ariboflavinosis

Studies of urinary excretion were made at levels of dietary intake of 0.55, 0.75, 0.85, 1.1, 1.6, 2.15, 2.55 and 3.55 mg per day. Data were recorded on 24-hour urine samples and on samples obtained during the 4 hours after subcutaneous administration of 1 mg of riboflavin. The results obtained by both techniques parallel each other. Subjects exposed to little or no trauma or irritation and receiving 1.6 mg of riboflavin per day excreted 4 times as much riboflavin as those on a 1.1-mg intake. This suggests that the critical riboflavin requirement for an adult male subsisting on 2,200 calories is somewhere between 1.1 and 1.6 mg of riboflavin per day. Healing of the skin lesions characteristic of ariboflavinosis is retarded when the 24-hour urinary excretion of riboflavin is less than 50 μg. Such a level may be reached in less than 4 months on a diet containing 0.55 mg of riboflavin per day. A subject depleted in riboflavin can satisfactorily assimilate at least 6 mg of riboflavin at one time. This was borne out by results which indicated that three 2-mg doses at 4-hour intervals were not more effective in repleting a deficient subject than a single dose of 6 mg of riboflavin in 24 hours. A period of approximately 15 days is required to saturate riboflavin-depleted subjects when a daily supplement of 6 mg of riboflavin is administered.