Riboflavin Metabolism of Women on Controlled Diets

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Abstract
Riboflavin metabolism was studied in 7 adult women on a controlled diet. The diet met the recommended allowances of the National Research Council in all known nutrients except for thiamine and riboflavin. Daily fasting values averaged 3.21 µg % for 208 determinations of serum total riboflavin and 1.41 µg % for 207 determinations of serum free (+ FMN) riboflavin. Urinary excretions of riboflavin varied from 315 to 467 µg per 24 hours and ranged from 27 to 40% of the riboflavin intake. The effects of an oral test dose of riboflavin were studied. The concentration of riboflavin in the serum reached a peak in one-half to one hour after the test dose and approached the fasting level in 5 hours. The peak in urinary excretion of riboflavin occurred one hour after the test dose and by the 5th hour the excretion of ribotlavin was about the same as the one-hour fasting excretion. Based on the excretion of riboflavin in terms of micrograms of urinary riboflavin per gram of urinary creatinine, the results of this study indicate that for two of 7 subjects, 1.2 mg per day of riboflavin may have been inadequate under the experimental conditions which obtained.