To the Editor.— A current health food fad involves tablets ofSpirulina,1a genus of blue-green algae belonging to the family Oscillatoriaceae of the division Cyanophyta,2represented in the health food literature to contain large amounts of vitamin B12. We subjected three popular brands of 500-mgSpirulinatablets to both theUnited States Pharmacopeiamicrobiologic assay for vitamin B12and the vitamin B12 radioassay method we recently applied to multivitamin pills.3 The results are given in the Table. Microbiologic assay would lead one to believe that 500-mgSpirulinatablets contain about 0.25 to 1 μg of vitamin B12per tablet, but radioassays, using R binder to measure the total of (cobalamins plus cobalamin analogues) and intrinsic factor to measure cobalamins alone (ie, "true B12"), suggest that more than 80% of what appears to be "vitamin B12" by microbiologic assay is in fact
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Herbert et al. (1982) studied this question.