Vitamin D2, molecular model. The chemical formula for vitamin D2, also called ergocalciferol, is C28.H44.O. Atoms are represented as spheres and are colour-coded: carbon (blue), hydrogen (gold) and oxygen (red). Vitamin D2 is an essential vitamin that cannot be made by the body. It is found in oily fish, dairy products and eggs. Another form of vitamin D, vitamin D3 (cholecalciferol), is made by the body, but only when the skin is exposed to sunlight. 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.