Spirulina and Vitamin B12

To the Editor.— A current health food fad involves tablets of Spirulina , 1 a genus of blue-green algae belonging to the family Oscillatoriaceae of the division Cyanophyta, 2 represented in the health food literature to contain large amounts of vitamin B 12 . We subjected three popular brands of 500-mg Spirulina tablets to both the United States Pharmacopeia microbiologic assay for vitamin B 12 and 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-mg Spirulina tablets contain about 0.25 to 1 μg of vitamin B 12 per tablet, but radioassays, using R binder to measure the total of (cobalamins plus cobalamin analogues) and intrinsic factor to measure cobalamins alone (ie, "true B 12 "), suggest that more than 80% of what appears to be "vitamin B 12 " by microbiologic assay is in fact