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The Effect of Nitrogen Intake upon the Urinary Riboflavin Excretion of Young Male Adults

Department of Home Economics, College of Agriculture, University of Illinois, Urbana

During the spring seasons of 1955 and 1956, 14 healthy male subjects, 22 to 27 years of age, were maintained on diets containing approximately zero, 2.5, 4.5, and 17 gm of nitrogen during consecutive periods of 12, 10, 10 and 10 to 15 days, respectively. Riboflavin intake was held constant at 1.6 mg. Urinary riboflavin and urinary and fecal nitrogen were determined.

As the nitrogen balance became more positive, and as dietary and urinary nitrogen increased throughout the study, the urinary riboflavin decreased. For example, in 1956, the average nitrogen balances for 7 subjects were -2.990 ± 0.3559; -1.293 ± 0.3013; -0.096 ± 0.3626; +3.752 ± 0.5768; and 3.868 ± 0.5899 gm for the first through the 5th periods, respectively. The riboflavin excretion values (in micrograms) for comparable periods were 723 ± 104.1; 526 ± 37.1; 459 ± 46.2; 277 ± 77.3; and 295 ± 92.5. The data on the relationship between urinary riboflavin and nitrogen were interpreted on the basis of labile and stable protein reserves with the assumption that the flavoproteins may be part of the labile rather than stable protein.

Unusually large amounts of riboflavin (mean value, 1186 ± 341.8 µg) excreted in the urine during the first three days of the study may have been influenced by pre-study diets and severe changes in nitrogen intake.

This study again stresses the point that, in attempting to set a requirement for riboflavin on the basis of urinary riboflavin excretion, the intake of protein and the nitrogen balance must be considered in the experimental plan and in the conclusions drawn.

² Present address: 128 South Nineteenth Street, Philadelphia 3, Pennsylvania.

³ Present address: 908 John Street, Kalamazoo, Michigan.

Manuscript received 20 March 1959.