FATS 465 



A shift in one double bond of ergosterol produces vitamin D. 

 This is accomplished by irradiation. 



Following the discovery of vitamin D by McCollum in 1921 

 there came a succession of announcements concerning it; Barger 

 of Edinburgh found that ergosterol could be activated by sunlight 

 so as to confer upon it antirachitic properties. Windaus of 

 Gottingen confirmed this and carried the work further. Hess 

 of New York announced that certain foods could be endowed with 

 antirachitic properties. Steenbock of Wisconsin soon followed 

 with work on the activation of foods by ultraviolet rays. Then 

 (1926) Barger showed that ergosterol and not cholesterol is the 

 sterol fraction in which the activity resides and which becomes 

 effective when irradiated. Ergosterol is now believed to be 

 the only sterol that can be endowed with antirachitic properties 

 by irradiation. 



When ergosterol is irradiated with ultraviolet light, it is 

 activated, that is to say, converted into a form that is potent 

 from one that has no curative action whatever on rickets. Either 

 sunlight or artificial illumination (if rich in ultraviolet) is success- 

 ful for radiation. That part of the ultraviolet spectrum lying 

 between 315 and 240 m^i is used. The physical change caused 

 by radiation is assumed to be a reorientation in molecular 

 structure or in electronic arrangement; that is to say, activation 

 consists not in a chemical change such as oxidation but in an 

 isomerization — a rearrangement of bonds (as already stated, 

 probably a shift in one of the double bonds). Only substances 

 containing ergosterol, such as cholesterol, can be activated by 

 radiation. Vitamin D in natural cod-liver oil is believed to 

 be activated ergosterol. When ergosterol is radiated to its maxi- 

 mum amount, it is 250,000 times more potent than cod-liver oil, 

 which has only 1 part in 20,000,000 of the active principle. If 

 radiation is carried too far, the potency drops. The activated 

 state of ergosterol lasts only a few days unless the substance is 

 dissolved in an oil; it is then good for months. In this form, it 

 is sold commercially for use in medicine. C. E. Bills separated 

 an ergosterol mixture into two related sterols, one of which was 

 ergosterol and the other isoergosterol. 



There is no trustworthy chemical or physical test for the 

 activated state of ergosterol, the only test for its potency as a 

 cure for rickets being a physiological one {i.e., through experi 



