The specificity of ergosterol as parent substance of vitamin D

Abstract

A review of the literature dealing with the discovery of ergosterol as the most potent source of vitamin D directs attention to the chemical structure of the sterols that make possible this property: (1) an OH group, (2) one or more unsaturated C linkages, and (3) a system of 4 reduced rings. Up to this time the OH group has not proven to be the active one. Saturated sterols are inactive. Neither single-bonded sterols, as cholesterol, nor the double-bonded have been found active. Substances with a chain of double-bonded carbons but no sterol rings are likewise inactive. A study was undertaken to determine whether isomers of ergosterol might be activated. Sphingosin, oxycholesterylene, iso-ergosterol, and digitaligenin were all found inactive by biological methods verified with spectroscopic tests. While digitaligenin absorbed the ultra-violet, the spectrum was entirely different from that of ergosterol. Windaus and Holtz had previously reported digitaligenin as potent after irradiation. Their findings are criticized because they dissolved the digitaligenin in olive oil, a substance which can itself be made potent by irradiation. When alcoholic solutions were used no such results were obtained. The evidence would indicate that only ergosterol possesses the peculiar chemical structure that permits it to be photochemically converted into vitamin D.