METABOLISM OF THE B VITAMINS 369 



When higher levels of pyridoxine are administered, dermal excretion of 

 pyridoxine also occurs. 



Table 31. Average Dermal and Urinary Excretion of Pyridoxine and its Metabolites 



. Sweat (mg/8 hours) * 



pyridoxal + 4-pyridoxic 

 pyridoxine pyridoxamine* acid 



Subject 



1 



2 

 3 



— ■ — Urine (mg/24 hours) 



pyridoxal + 4-pyridoxic 

 pyridoxinef pyridoxamine* acid 



0.114 

 0.187 

 0.118 



0.192 

 0.375 

 0.236 



2.83 

 3.02 

 3.29 



0.030 

 0.030 

 0.032 



0.159 

 0.193 

 0.257 



* Measured in terms of pyridoxal. 



t The data cannot be accepted in a quantitative sense, because the assay methods used are now known 

 to give results that do not represent the specific analogues indicated. The data do illustrate the points 

 cited in the text, however. 



Individual Variations. Despite the fact that there may be large daily 

 variations in the excretion of most of the B vitamins, marked individual 

 differences do exist of such a nature that for some of the B vitamins, 

 two individuals on the same dietary intake may excrete widely divergent 

 amounts. This is to be expected in consideration of the many genetically 

 controlled enzyme systems that mediate vitamin metabolism. Fecal B 

 vitamin excretion varies more than does the urinary excretion, since the 

 bulk of fecal vitamins is controlled by the bacteria present rather than 

 by the host; but even in this case individuals do differ by virtue of these 

 differences in intestinal tracts, etc. This may be noted, for instance, by 

 considering the values in Table 29 for subjects 4 and 6. These subjects 

 were brothers, and a distinct resemblance occurs in the urinary and fecal 

 excretion of both thiamine and riboflavin. 



An excellent example of urinary individual differences is that of thia- 



Table 32. Urinary and Fecal Excretion of Thiamine and Pyramin by Six Men on 



Three Days* 



* In the above table, the measurements of thiamine were not made on the same three days as were 

 the measurements of pyramin. 



t Expressed as 2-methyl-4-amino-5-ethoxymethylpyrimidine. 



