Vitamin D3, molecular model. The chemical formula for vitamin D3, also called cholecalciferol, is C27.H44.O. Atoms are represented as spheres and are colour-coded: carbon (blue), hydrogen (gold) and oxygen (red). Vitamin D3 is produced by the body when the skin is exposed to sunlight. Another form of vitamin D, vitamin D2 (ergocalciferol), is an essential vitamin that cannot be made by the body. It is found in oily fish, dairy products and eggs. Vitamin D is necessary for absorbing calcium and phosphorous in the gut. Deficiency can lead to bone disorders such as rickets (improper bone formation) in children, and osteomalacia (bone softening) and osteoporosis (brittle bone disease) in adults.