The importance of recognizing secondary vitamin deficiencies cannot be overemphasized in evaluating nutritional results, whether we are dealing with experimental animals or human beings. It is quite likely that many of the conflicting or apparently conflicting results reported in nutrition literature are due to a failure to recognize and take into account these disturbing secondary effects.
That the dangers of secondary deficiencies have long been recognized in nutrition is demonstrated by the dietary precautions in the early biological assay methods, namely, that the basal diet be deficient in the test vitamin only and “adequate in all other respects” (1).
Nor is the idea of the interdependence of the vitamins a new one. For many years nutrition literature has been replete with such illustrations.