Vitamin D 25 (OH) is both a hormone and vitamin. Composed of a group of fat-soluble secosteroids, Vitamin D enhances intestinal absorption of calcium, iron, magnesium, phosphate and zinc, playing a crucial role in human bone health. Its chief components are Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol). While both can be ingested from supplements, few foods contain Vitamin D. Sun exposure acts as the main source of Vitamin D3 in humans but is dependent on UVB radiation and often limited by sunscreen, other barriers or time spent outdoors as measures to reduce the risk of cancer.