Vitamin D sources. Conceptual illustration showing balloons, eggs and sunshine. The body synthesizes vitamin D when exposed to sunshine. Vitamin D is also found in foods such as oily fish, milk, liver, egg yolk and fortified cereals. It 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.