Rickets. Rear view of the bowed legs of a patient due to rickets, a disorder usually caused by a lack of vitamin D in the diet during childhood. Vitamin D is needed to make the bones take up calcium and phosphate as they grow. Without these two components, the bones become soft and those in the legs bow outwards under the weight of the body. The spine and skull may also be affected. Vitamin D is also produced by the skin on exposure to sunlight, and a lack of sunlight during childhood may also cause the disease. Vitamin D supplements can restore normal bone growth, and with such treatment bone deformities disappear as the child grows.