FACTORS INFLUENCING B VITAMIN REQUIREMENTS 273 



tually unstudied and present a field of real interest for obvious reasons. 

 Other aspects of disease and its interrelationships with B vitamins are 

 more fully presented in Chapter VI C. At present it is possible to do little 

 more than recognize the existence of a vast and unstudied group of so- 

 called "conditioned nutritional deficiencies," wherein pathological con- 

 ditions have raised individual B vitamin requirements. 



It has previously been mentioned (p. 247) that the thiamine require- 

 ment varies with the metabolic rate of an individual. Under conditions 

 in which there is an augmented metabolism (hyperthyroidism, prolonged 

 fever) the requirement is therefore notably increased. Details as to the 

 extent of this increase are lacking, however. 



Inherent Individual Variations in B Vitamin Requirements. When 

 finally we consider the existence of the many factors which go to delineate 

 the vitamin requirements of a species and a strain under highly defined 

 conditions, we are still faced with the indisputable fact that individual 

 animals, and indeed litter mates, differ from each other in many ways, 

 among which are their B vitamin requirements. R. J. Williams, in a more 

 extended discussion of the aspects of individual variability in metabolic 

 patterns, has pointed out the extreme importance of such variation. He 

 states: 48 



"It would be presumed on the basis of what we know about the inherit- 

 ance of enzyme catalysts and the heritability of vitamin requirements in 

 animals that the requirements for each vitamin would be inherited as a 

 separate unit. A requirement for one vitamin might be very high, for 

 another it might be low, and for a third it might be about average, and 

 so on. The inheritance of individual vitamin requirements, which is closely 

 akin to the inheritance of enzyme catalysts, does not rule out the fact 

 that environmental conditions such as infectious disease may alter re- 

 quirements and make for variation, though information on this point is 

 largely lacking. . . ." 



"On the basis of what we know about the requirements of animals it is 

 safe to assume that individual human beings differ widely from one 

 another in the amounts of different vitamins that they require. It is not 

 at all improbable that specific individuals may have requirements for 

 certain vitamins which are several times those of their associates. These 

 differences may be due to relative failure to digest or assimilate, in- 

 creased tendency to excrete, a failure in the ability to build the vitamins 

 into the tissues, or to other reasons." 



"As I have said, information on variation in vitamin requirements is 

 largely lacking; those who have been investigating vitamins in nutrition 

 have not been interested in possible individual differences but have been 

 pleased if they could get information about the average man, and have 



