398 RIBOFLAVIN 



less riboflavin in their muscle and liver than those of the A strain on the 

 same diet. 



5. Other Factors 



There have been suggestions that the growth requirements of male and 

 female rats are different,^- the over-all effects of riboflavin deflciency being 

 more prominent in the male. Unhke thiamine deficiency, the lack of ribo- 

 flavin is not associated with severe anorexia; thus, appetite is not so im- 

 portant a factor in riboflavin depletion studies. The interrelationships be- 

 tween riboflavin and other vitamins of the B group have been studied.^" 



B. OF MAN 



In the absence of experimental data on human subjects, the e^mation 

 of riboflavin requirements is based upon average dietary consumptions or 

 upon extrapolations of data from animal experiments. Calculation of aver- 

 age consumption is not a satisfying procedure, since different locales will 

 show great variations depending upon dietary habits and the availability 

 of riboflavin-rich foods. Attempts to calculate man's needs from data on 

 rat growth tend to give figures which are too high to be practical. It is 

 therefore necessary to test vitamin requirements on man, himself. 



It is logical to expect that the minimum requirements of human beings 

 would be much more variable than for the inbred laboratory animal. That 

 this is the case was illustrated by Horwitt et al.,^ • ^^ who studied fifteen men 

 on a diet providing 0.55 mg. of riboflavin per day. Three of the men de- 

 veloped relatively severe dermatological lesions, nine men showed mild 

 symptoms of ariboflavinosis, and three others had no symptoms at all. 



Excretion studies which compare the amount of riboflavin intake with 

 the amount excreted in the urine have been used for many years as a means 

 of estimating human requirements. Much confusion has resulted from this 

 approach because there is, as yet, no agreement upon how much riboflavin 

 should be excreted before the intake is considered adequate. 



In some of the older studies on riboflavin excretion*^ "*^ the diet Avas not 

 considered adequate if it contained less than 2 mg. of riboflavin per day. 

 Consequently, urinary excretions of less than 500 meg. per day were desig- 

 nated as deficient. More recent comparative studies on the amounts of 

 riboflavin excreted in the urine on different levels of intake have shown that 



40 K. Bhagvat and P. Devi, Biochem. J. 45, 32 (1949). 



•»! O. W. Hills, E. Liebert, D. L. Steinberg, and M. K. Horwitt, Arch. Intern. Med. 



87, 682 (1951). 

 "2 A. Emmerie, Nature 138, 164 (1936). 

 " F. M. Strong, R. S. Feeney, B. Moore, and H. T. Parsons, ./. Biol. Chem. 137, 363 



(1941). 

 " V. n. Fedor, G. T. Lewis, and H. S. Alden, ,/. Nutrllion 27, 347 (1944). 



