Elevated Riboflavin Levels in Urine of Fasting Human Subjects

Abstract

The urinary excretion of riboflavin in fourteen of fifteen normal subjects increased during a 24 to 37 hour fast. In most subjects, the increased rate of excretion did not start until 13 to 20 hours after the last meal. The total 24-hour riboflavin excretion during the fast was about twice that for the last day when food was consumed. Toward the end of the fast, the excretion rate of riboflavin in some subjects was ten to fifteen times that for the control day. The amount of nitrogen and creatinine excreted during the fast was essentially the same as for the control day.