Abstract
<h3>To the Editor.—</h3> A current health food fad involves tablets of<i>Spirulina</i>,<sup>1</sup>a genus of blue-green algae belonging to the family Oscillatoriaceae of the division Cyanophyta,<sup>2</sup>represented in the health food literature to contain large amounts of vitamin B<sub>12</sub>. We subjected three popular brands of 500-mg<i>Spirulina</i>tablets to both the<i>United States Pharmacopeia</i>microbiologic assay for vitamin B<sub>12</sub>and the vitamin B12 radioassay method we recently applied to multivitamin pills.<sup>3</sup> The results are given in the Table. Microbiologic assay would lead one to believe that 500-mg<i>Spirulina</i>tablets contain about 0.25 to 1 μg of vitamin B<sub>12</sub>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<sub>12</sub>"), suggest that more than 80% of what appears to be "vitamin B<sub>12</sub>" by microbiologic assay is in fact
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