The Multiple Nature of the Vitamin D of Fish Oils

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Abstract
The liver oils of twenty-five species of fish were assayed in comparison with cod liver oil on rats and chickens. Rat unit for rat unit, some resembled cod liver oil, several were definitely less effective, and a few were more effective than cod liver oil. The oils which were relatively the least effective were those from bluefin tuna of California, oriental tuna, striped tuna, bonito, albacore and totuava. The relatively most effective oil was that from the white sea-bass of California. The maximum observed difference in relative effectiveness was about eighteen times, a difference much greater than the probable errors of assay. As possible causes of the differences, the following were eliminated: Existence of vitamin D in conjugated forms of unequal availability, synergism or antagonism of vitamin A, presence of free fatty acids, and the nature of the oily vehicle. It was concluded that the differences were due to the existence of two or more forms of vitamin D in the oils. The possible relation of the fish oil vitamins D to certain artificial forms, particularly irradiated ergosterol and irradiated 7-dehydrocholesterol, was discussed. The relative effectiveness of irradiated ergosterol was lower than that of any fish oil. The relative effectiveness of irradiated 7-dehydro-cholesterol was about the same as that of cod liver oil or irradiated ordinary cholesterol, but inferior to that of white sea-bass liver oil. Oils of related species, particularly the several tunas, differed widely in relative effectiveness. The findings support the view that the big tunas formerly classed as Thunnus thynnus actually comprise several species, of which we have studied T. saliens, T. orientalis and T. secundodorsalis.

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