252 



VITAMINS 



shown by a wide variety of antibacterial agents and is probably due to 

 destruction of intestinal microorganisms which otherwise compete with 

 the animal for essential food factors. 



Very recently Wetzel et al. have reported that doses of 10 /Ag. of vita- 

 min Bi2 given daily by mouth to a group of malnourished school children 

 resulted in definite stimulation of growth in 5 of the 11 cases treated. 

 These results establish the existence of human vitamin B12 deficiency 

 other than that of pernicious anemia. How extensive this may be remains 

 to be determined by further study, but present indications are that vita- 

 min B12 may well prove to have wide applications in human nutrition. 



The metabolic function of vitamin B12 in the animal body is evidently 

 closely related to that of pteroylglutamic acid (for example, both are 

 effective in certain types of anemia). Specifically, vitamin B12 appears 

 to take part in the biosynthesis of nucleic acids and in the formation 

 and use of active methyl groups in the body (for example, in the forma- 

 tion of methionine from homocystine) . 



Food sources and requirements 



As already indicated, vitamin B12 is more concentrated in foods of 

 animal origin than in plant products, and relatively large amounts are 

 formed during the growth of many microorganisms. The distribution of 

 this vitamin in various foods, as determined by Elvehjem and co-workers 

 by means of a rat assay method, is shown in Table 9-6. No figure for 

 the normal human requirement for vitamin Bio has been established, but 

 1 ixg. per day, if injected, is sufficient to maintain pernicious anemia 

 patients in good condition. This amount is much less than the minimum 

 human requirement of any other vitamin or trace element. 



Table 9-6 

 Vitamin B12 content of foods 



(Micrograms per 100 g., fresh basis) 



Food 



Barley 



Beans 



Beef, liver 



Beef, kidney 



Beef, round, cooked 



Beef, tongue 



Cabbage 



Cheddar cheese .... 



Chicken liver 



Cow's milk 



Minimum vitamin 



Bi2 content 

 * 



* 



15 

 20 

 2-3 



3 



* 



1.4 

 11 



Trace 



Food 



Egg yolk 



Goat's milk 



Green peas 



Horse meat, canned 



Mutton 



Pork, shoulder 



Pork, ham 



Potatoes 



Tomato juice 



Veal 



Minimum vitamin 



B12 content 



1.4 



* 



* 



3.4 

 3 



1.1-2 



1.2 



* 



2 



* No measureable amount. 



