Rickets is a condition of abnormal bone development in children. In rickets the process of calcification and hardening of bones is disordered. Rickets results in abnormal bone formation that can be associated with pain, growth disturbance and deformity such as bowed legs (where the knees turn outwards). There are many potential causes of rickets: a poor diet lacking in vitamin D and calcium is the most common cause, as these are both essential for normal bone formation. Rarer causes include an inability for the body to absorb or process vitamin D or other minerals. If these problems are present in an adult the condition is called osteomalacia. Sources of vitamin D include sunlight and certain foods such as oily fish. Certain foods also have vitamin D added to help prevent rickets, including cereals. Foods that are high in calcium include dairy products and green leafy vegetables.