“Vitamin D from skin or dietary sources does not circulate for long in the bloodstream, but instead is immediately taken up by adipose tissue or liver for storage or activation. In humans, tissue storage of vitamin D can last for months or even years.”

“Cod liver oil is now being produced without the help of codfish by a process perfected by Dr. Charles E. Bills, of Evansville, Indiana. The power of cod liver oil to build bones and prevent rickets is attributed to the presence in it of a chemical substance, ergosterol. This substance is also found, in an inactive state, in yeast and in certain fungi, and can be made active by exposure to ultra-violet rays, either from the sun or from artificial sources. The yeast ergosterol is then dissolved in peanut and cottonseed oils.”

“The discovery that vitamin D in fish liver oil has an antirachitic effect (E. Mellanby, 1919) led to a considerable production of this commodity until about 1930. At this time, the practice of UV irradiation of foods, to increase their vitamin D content, began. The photochemical production of vitamin D2 from ergosterol and of vitamin D3 from 7-dehydrocholesterol was also initiated, so that the use of fish liver oil became less important. The development of synthetic vitamin D in turn replaced the irradiation of foods, mainly because of the difficulty of controlling this process and also because of the necessity for biological activity assays. Thanks to the availability of synthetic vitamin D, the enrichment of foods with the vitamin proved the simplest method of providing the population with supplemental vitamin D. The production of vitamin D has increased from 35 lb in 1948 to 14,000 lb in 1972 [Holmes & Kummerow (1983)].”