FACTORS INFLUENCING B VITAMIN REQUIREMENTS 267 



again, however, the complete picture is not available. For example, it is 

 not entirely clear why the administration of higher levels of choline pro- 

 duces a considerable growth increase in female turkeys at 24 weeks, but 

 not in females at 10 weeks, nor in male turkeys at all. 15 Morris, Palmer, 

 and Kennedy, in studying the relationship of efficiency of food utilization 

 to inheritance in rats, 16 found that there were appreciable sex differences, 

 the average female efficiency being 70 per cent greater than that for the 

 male during the six-week study period. It seems likely, however, that 

 present advances in our understanding of the effect of the sex hormones 

 on metabolism in general, and in particular upon protein metabolism, 

 may ultimately serve to clarify certain of these relationships. 



Influence of Occupation. While it is commonly stated that persons 

 engaged in hard physical labor require an increased amount of vitamins 

 in their nutrition, there is little to support so sweeping a statement. 17 

 Nevertheless, the effect of work in increasing the caloric requirement 

 does undoubtedly bring about increased B vitamin requirements (but 

 probably not increased requirements for other vitamins), although this 

 increase may not be as great as for the caloric requirement. As con- 

 trasted with such hard physical labor, Forbes 18 has pointed out that 

 emotionally tiring work performed by the average industrial worker is 

 completely unstudied in regard to its effect on B vitamin requirements. 

 During recent years, as our understanding of nutritional values has 

 improved, there has been in the United States a tendency for the calorific 

 value of diets to rise. 13 Concurrently there has therefore been an increase 

 in B vitamin requirements, but there is little to indicate to what extent 

 the increased pace of life in these same years has influenced our nutri- 

 tional vitamin requirements. 



In occupations involving such extreme physical exertion that perspi- 

 ration is excessive, there is some possibility that increased vitamin excre- 

 tion affects the B vitamin requirement. This possibility is considered at 

 greater length in the paragraphs that follow. 



Effects of Climate. Throughout the war years there appeared a variety 

 of conflicting reports with regard to the effects of climate on vitamin 

 requirements. Many of these were particularly concerned with the thia- 

 mine requirement, which probably serves as an excellent criterion for 

 the problem in question. Since in tropical climates there is a decreased 

 caloric requirement, 19 it might be anticipated that there would be de- 

 creased B vitamin requirements. Despite this, Mills et at. 20 ' 21 found that 

 rats have increased thiamine requirements at higher temperatures, and 

 Sarett and Perlzweig 22 later extended these studies by measuring the 

 tissue thiamine in rats at different temperatures. Edison, however, found 

 that rats at 90° F and 70 per cent relative humidity required no more 



