Most commonly from lanolin, a grease extracted from sheep's wool. It's processed into (7-DHC), the same compound in human skin. 7-DHC is bombarded with UV lig

Most commonly from lanolin, a grease extracted from sheep's wool. It's processed into (7-DHC), the same compound in human skin. 7-DHC is bombarded with UV light, triggering a chemical reaction that creates Vitamin D3.