Chapter II C 



FACTORS INFLUENCING B VITAMIN REQUIREMENTS 



There are few aspects of an individual, his nutrition, or his environ- 

 ment that do not to an appreciable extent influence his B vitamin require- 

 ments. These effects may be exerted by (a) varying the actual physi- 

 ological requirement, (b) varying the proportion of the total vitamin 

 intake which may be utilized, or (c) varying the amount of vitamin 

 supplied by intestinal flora. The ensuing discussion of these effects pro- 

 ceeds in that order. To consider even a major portion of the factors in- 

 volved would be neither possible nor practical in this volume. Rather, it 

 seems expedient to consider briefly those major factors which have proved 

 to be the most important in influencing B vitamin dietary requirements. 

 It is impractical to do more than briefly delineate these relationships at 

 this time, although a more fundamental explanation of their basis in 

 many cases is provided in the succeeding chapters. 



Factors Influencing the Physiological Requirement for the B Vitamins 



Species and Strain Variability. Thiamine was the first of the B vitamins 

 to be discovered and thoroughly studied, and consequently knowledge of 

 the variability of its requirement among different species is perhaps the 

 most complete of all. Since many of the more recently discovered 

 members of the B vitamin family follow the same trends as does thiamine 

 in this regard, it is advantageous to consider vitamin Bi in greater detail 

 from this standpoint than would otherwise be the case. 



We have previously mentioned (p. 246) Cowgill's extensive study of 

 species requirements and his conclusion that smaller species require a 

 greater amount of thiamine per unit of body weight than do larger ones. 



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