318 THE BIOCHEMISTRY OF B VITAMINS 



need some, and may in the future be shown to need most, of the B vitamins 

 required by other organisms. 



The B Vitamin Requirement of the Vertebrates 



Since we have considered earlier the many factors that may so pro- 

 foundly influence B vitamin requirements, it would indeed be strange to 

 set down absolute specifications for the vitamin intake of man or any other 

 species. A casual survey of the literature reveals data pertaining to the re- 

 quirements of many species, and in some cases, excellent reviews of the 

 requirements of a particular species are available (man, 53 mouse, 54 birds, 56 

 pigs, 57 ruminants, 58 other animals 59,181 ). For the sake of convenience 

 alone some of the useful data are reproduced here in tabular form. Any 

 discussion of their validity, however, would be redundant, and is de- 

 liberately avoided. In addition, the current National Research Council 

 table of recommended daily dietary allowances for humans is here repro- 

 duced for the convenience of those who are constrained to settle upon 

 some figure for dietary calculations. 00 The amounts cited in this table, 

 as in any other, might well be subjected to extended discussion, but a 

 critical appraisal of human B vitamin requirements would require a 

 volume in itself. 61 It may be said, however, that it would be difficult for 

 practical reasons to construct a diet meeting the stated allowances that 

 was still inadequate in B vitamin content. It is thus hoped that the salient 

 fact emerging from our discussion of B vitamin requirements is that even 

 in a monograph devoted to the subject of the B vitamins, the authors 

 cannot conscientiously make a statement as to the precise requirements 

 of any species for any vitamin. 



Reference was made earlier to Cowgill's comparison of the thiamine 

 requirements of different species (p. 246). It would be expected that a 

 similar general relationship would hold for the other B vitamins, and 

 this is apparently so, judging from the limited data available. Despite 

 the many errors, qualifications, and interpretations inherent in any presen- 

 tation of such data, Figures 5 to 14 are presented, to emphasize the 

 general trend that exists for smaller species to have a higher relative B 

 vitamin requirement than larger ones. 183 



When one considers at length the conflicting evidence regarding whether 

 or not various animal species require certain B vitamins, the conclusion 

 is inevitably reached on the basis of the existing evidence that all the 

 species studied require an exogenous source of all the B vitamins, with 

 the probable exception of nicotinic acid (and choline, although this has 

 "nonvitamin" functions and the requirement should be considered in a 

 different light because of this) . In those cases where there is no nutritional 

 requirement, intestinal flora account adequately for the discrepancy. In 



