The author reflects on updates on the research and development of vitamin D as a pro-hormone supplement. Other topics include the discovery by Dame Harriette Chick and co-workers of cod liver oil supplementation as treatment for rickets in children in Austria 100 years ago as of 2022, the high vitamin D content of said oil, the research by Chick on how vitamin deficiencies cause diseases, and the vitamin D precursor called 7-dehydrocholesterol.