Requirements and Occurrence in Foods

Vitamin B12 is found only in foodstuff of animal origin such as meat, offal, eggs, milk, and cheese. The vitamin is not present in any fruits, nuts, or green leaf vegetables. Claims to the contrary are usually the result of con- 

Cow s milk contains between 1.6 and 6.2 pg of vitamin B12 per 500 ml and this is sufficient to provide the daily requirement of man. However, if milk is boiled much of the vitamin B12 content may be lost and that remaining may not be sufficient to prevent overt signs of vitamin B12 deficiency. Pasteurization of milk results in the loss of up to 10% of vitamin BI2 (C7). 

In certain health food literature, Spirulina, a blue-green algae, has been claimed to be a source of vitamin B12. It appears that this was based on the results obtained from the United States Pharmacopeia microbiological assay for vitamin B12. This assay uses Lactobacillus leichmannii as the test organism and it is known that this organism responds to some vitamin B12 analogs. Herbert and Drivas (H7) found that analogs of the vitamin accounted for more than 80% of what appeared to be vitamin B12.  

Although measurement of the concentration of vitamin B12 in serum is the most widely used test for the investigation of a possible deficiency, there are a number of other tests used to measure absorption, the integrity of the methylmalonyl metabolic pathway, and the presence of antibodies to intrinsic factor. These additional tests are also described in this section. 

Measurements using radioisotope dilution techniques are rapid and the more recently designed kits appear to be reliable in skilled hands. 

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