What is vitamin D? The role of cholesterol and the sun

Vitamin D is a collective name for a fat-soluble hormone-like substance that we absorb through our food or that is made by exposure to sunlight. The ultraviolet light contained in sunlight converts the cholesterol in our skin into active vitamin D, aided in this task by the liver and kidneys. Our bodies can also create vitamin D through our cells. We also absorb vitamin D through food or supplements in plant, chemical or animal form. Vitamin D is also available to us as a bioactive ergocalciferol or calciferol (plant-derived vit. D2) or cholecalciferol (animal- or often chemical-derived vit. D3).

The amount of Vitamin D is expressed in micrograms of ergocalciferol for vitamin D2 (plant-derived) or micrograms of cholecalciferol for vitamin D3 (animal-derived). In supplements D3 is generally created using chemical processes.