370 THE BIOCHEMISTRY OF B VITAMINS 



mine excretion, as shown in Table 32. The subjects in this study of 

 Mickelson et al. 171 were on a thiamine intake of approximately 1.5 mg per 

 day, and under these conditions distinct differences are shown in thia- 

 mine excretion among the subjects. Pyramin excretion, however, was 

 most remarkably constant from day to day and individual to individual, 

 and has been suggested for this reason as a more accurate indication of 

 the status of thiamine nutrition as judged by excretion studies (p. 256). 

 It will be noted that fecal thiamine does not vary with either the thia- 

 mine or pyramin excretion in the urine. Certainly the investigation of 

 the source and high variability of fecal pyramin would seem to be a 

 worthwhile undertaking, together with the extension of this study to a 

 larger number of individuals. 



Relationship to Dietary and Body Levels. The levels of the various B 

 vitamins found in the urine do not correlate with the requirements for 

 these vitamins because of the variety of ways in which the various mem- 

 bers of the group are metabolized. Above a certain minimal level, the 

 amount of a vitamin in the diet is generally correlated with its content in 

 the urine. In a general manner, the levels in the urine resemble those in 

 milk and in sweat. As yet there are insufficient data to tell whether this 

 is also true of saliva. The addition of some one vitamin in a single high 

 dose to the diet of an individual "saturated" with a B vitamin causes an 

 increase in the blood level rather rapidly, but an almost equally rapid 

 fall to normal and corresponding increase in the urine. A full understand- 

 ing of these relationships, however, must await the elucidation of the 

 variations which occur in the various B vitamin derivatives, the fate 

 of the unaccounted for fraction of the intake, and the source and qualita- 

 tive nature of the fecal fraction of the vitamins eliminated. These prob- 

 lems at present are all under intensive investigation, and may well be to 

 a large extent resolved in the near future. 



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