Riboflavin in the Blood and Urine of Women on Controlled Diets

Determinations of the riboflavin content of various fractions of fasting blood and of concurrent 24-hour urinary excretions were made for 7 subjects during 30 days of a controlled riboflavin intake of 1.4 mg per day and for bound and free riboflavin in the fasting blood of 59 women with unrestricted intake. The ability of the individual to maintain a characteristic level of riboflavin in each blood fraction was demonstrated, although individual differences for the white cell fraction were not as distinct as for the other fractions. There appeared to be a gradual trend toward lower levels for red cell riboflavin for all subjects. Adaptation to a change in intake was apparent in the trends for urinary excretion of riboflavin for all subjects during the first 14 days. Very large excretions of riboflavin were observed for an obese subject on the controlled intake.