RIBOFLAVINE 



aiid the dietary intake of riboflavine in many species of animals, in- 

 cluding man, but the relationship does not appear to be as simple 

 as with some other members of the vitamin B complex. A group of 

 rats on an adequate diet excreted 24-6 /ng. per day in the urine, ^ whilst 

 other rats on a poor diet excreted only about 2/>ig. per day.'' A horse 

 excreted 1-5 mg. per day,^ but this value fell to less than 30 /xg. per day 

 on a restricted dietary intake of riboflavine. Following the oral 

 administration of large amounts of riboflavine a very large apparent 

 increase was observed in the amount excreted by goats and sheep, 

 when the fluorimetric method of assay was used, whereas an increase 

 of only about 20 % was observed when microbiological assays were 

 employed.^ With rats and humans on the other hand, good agree- 

 ment was obtained between the microbiological and fluorimetric 

 values. 



Women on an adequate diet excreted 357 /xg. of riboflavine per day 

 in the luine, and this value fell to 77 fig. per day on a diet containing 

 only 0*5 mg. of riboflavine per 2400 cals.^ Other values recorded 

 for the urinary excretion of humans on adequate diets were 320 to 

 360 /xg. per day,' and 500 to 800 /xg. per day.^ In the last group of 

 subjects the excretion fell rapidly to 50 to 150 /xg. per day when the 

 intake dropped to i to 2 mg. per day, and rose again on increasing 

 the intake to 2 to 5 mg. per day. In another experiment, ^^ the average 

 daily urinary excretions on diets containing 0-28, 0-49, o-66 and 7-1 

 mg. per 1000 cals. were 119, 107, 150 and 263 /xg. respectively, and 

 increased to 325 /xg. after two weeks on a diet supplying 9-63 mg. per 

 1000 cals. Still higher values were recorded by Brewer et al}^ daily 

 excretions of 70, 160, 130, 320, 1180 and 1310 /xg. being obtained on 

 daily intakes of 079, 1-04, 1-26, 1-62, 2-23 and 272 mg. per day. 

 Infants excreted 35 to 50 /xg. per day on a diet deficient in ribo- 

 flavine.^^" 



On self-selected diets supplying 1-25 to 2-47 mg. of riboflavine per 

 day, young women excreted ^^^ 36 to 50 % in the urine and 27 to 54 % 

 in the faeces ; following a 5-mg. supplement, between 24 and 44 % 

 was eliminated in the urine. In no instance did the urinary and 

 faecal excretion together exceed the intake. Oldham et al.'^^ observed 

 a correlation between riboflavine excretion and nitrogen balance ; on 

 a diet providing i mg. of riboflavine daily for ten days, i-2 to 1-4 mg. 

 daily for a further ten days and i mg. daily for a further ten-day 

 period with nitrogen intakes of 5, 19, and 5 g. daily in each ten-day 

 period respectively, 40 to 60 % of the riboflavine was excreted in the 

 first and third periods, when the subjects were in negative nitrogen 

 balance, and 7 % when the subjects were in positive nitrogen balance. 

 The urinary excretion of riboflavine increased in protein deficiency, 

 and fell during recovery. ^^ 



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