Vitamin D is a type of fat-soluble steroid that can take two separate forms, vitamin D2 and D3, whose actual names are Ergocalciferol and Cholecalciferol. It is produced in the skin from exposure to ultraviolet radiation, the sun. This is the primary way to build up vitamin D, but it can also be ingested in foods which naturally contain it or are artificially fortified with it. However, what happens when the human body has a vitamin D deficiency? A new study from Oxford University shows that a lack of sufficient vitamin D in the body can lead to a wide range of diseases.