The absorption spectrum of vitamin D

Numerous studies have been made of the absorption spectrum of the products of ultra-violet radiation of ergosterol (1). These studies have shown that such radiation causes a decrease and final disappearance of the characteristic absorption band of ergosterol (maximum 280m μ). Several workers have reported the simultaneous formation of a new absorption band (maximum 240), and have attributed this band to vitamin D. Our own observations, however, have shown (2) that the first effect of ultra-violet radiation on ergosterol, and we have suggested that this is due to the formation of a new substance with an absorption maximum at 280, and that this substance is vitamin D (3). It has also shown that the product having maximum absorption at 240 has no detectable antirachitic activity (4). We have compared the antirachitic activity of irradiated ergosterol solutions with their absorption spectra, both before and after removal of unchanged ergosterol, and have obtained evidence pointing to the successive formation of three substances (or mixtures of substances). Of these, the first has maximum absorption at 280, and is, we believe, vitamin D; the second shows maximum absorption at 240, and has no antirachitic action; the third is similarly inactive, and shows no intense absorption. We propose to refer to these substances as A, B, and C, respectively.