584 NIACIN 



were given orally in man and animals /^"'^^ although some drugs seem to 

 produce an increased excretion of nicotinic acid metabolitesJ^"^^ The final 

 solution to this knotty question will have to await the availability of tools 

 which will permit a more direct approach to the problem. 



e. Influence of Fat 



Salmon^ ^ has shown that diets high in fat result in a lowered dietary 

 requirement for nicotinic acid, in a fashion similar to the well-known 

 thiamine-sparing action of fat. This has been interpreted as providing 

 additional evidence for the role of nicotinic acid in carbohydrate metabo- 

 lism, although the correctness of this interpretation has been questioned.®* 



/. Other Influences 



(1) Corn. The fact that the occurrence of human pellagra is so often 

 associated with the consumption of diets high in corn, and the fact that 

 pellagra will develop when corn diets are fed whereas other diets with less 

 nicotinic acid do not cause pellagra,^"' ^^ have led to innumerable attempts 

 to find some substance in corn which increases nicotinic acid requirements 

 (pp. 548 and 565). Although it has been shown that corn, under certain 

 circumstances, will increase nicotinic acid requirements in several species 

 of animals,^' ^^' ^^ there is no conclusive evidence that this effect of corn is 

 due to anything more than the effect of its low tryptophan protein.'*^- ^^' ^^ 

 The weight of evidence seems to favor the view that these effects of corn 

 can be adequately explained on this basis plus perhaps a relatively low 

 digestibility and a low availability of the nicotinic acid in corn.*"*- ^^ 



(2) Vitamin Bt,. A deficiency of pyridoxine in the rat, if sufficiently 

 severe, reduces the excretion of urinary nicotinic acid derivatives after 



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