Vitamin D2. Computer model of a molecule of vitamin D2 (ergocalciferol). Atoms are represented as spheres and are colour-coded: carbon (yellow), hydrogen (white) and oxygen (pink). This is the form of vitamin D found in supplements, it is not produced by the human body. Vitamin D is necessary for the absorption of calcium and phosphorous in the gut. Deficiencies in vitamin D lead to rickets (improper bone formation) in children, and osteomalacia (bone softening) and osteoporosis (brittle bone disease) in adults. Vitamin D is fat-soluble and found in foods such as oily fish, milk, liver and egg yolk.