From ancient times, in folk medicines, sunlight is used in the treatment of diseases such as rickets, a bone disease of infancy and childhood. Although vitamin D is commonly called a vitamin, it is not actually an essential dietary vitamin in the strict sense, as it can be synthesized in adequate amounts by most mammals exposed to sunlight.

Deficiency:
The severe forms of rickets and osteomalacia (Osteomalacia is a weakening of the bones) with  gross deformities of the skeleton are now rare. Only a few foods are good sources of vitamin D and the major part about 90 per cent of the vitamin in our bodies comes from photosynthesis (the process of absorption)  in the skin. Minor forms of the disease leading to impairment of bone growth in children and demineralization in adults, especially in old people, continue to be found in sections of the community in all countries.

Disease Pattern:
Rickets (major disease outcome of vitamin D deficiency) is characteristically most severe in children between the ages 1 and 3 years, when they are growing rapidly and the limb bones have to support an increasing weight.It often becomes more pronounced at puberty, associated with the growth spurt. Vitamin D deficiency is now recognised in very young infants, especially those born with low birth weights.

It is attributed to the mother being unable to supply sufficient vitamin to the foetus or subsequent in her milk.  Osteomalacia is classically a disease found in women, who through lack of vitamin D have been unable to replace calcium from their bones lost to the foetus at the time of conception and lactation.Elderly people  who for many reasons may be restricted in their physical activity may not get sufficient exposure to sunlight to meet their needs for vitamin D.

Risk factors
1. Inadequate exposure to sunlight: Long winters with only a few hours of day light greatly reduce exposure to ultraviolet radiation. Vitamin D deficiency is then a risk for all children and adolescents as they have grater need for the vitamin than adults.
2. Unrefined cereals can prove to be another such risk factor.
3. Vegetarianism: People who eat no animal food exhibit an increased proportion in case of osteomalacia.
4. Prolonged breast feeding: When an infant is fed exclusively on milk from a vitamin D deficient mother for more than three months, the risk of infantile rickets rises.
5. Skin pigmentation: Heavy pigmentation reduces synthesis of vitamin D in the skin. This can only be a minor risk factor.

Clinical Features(in children):
In children, vitamin D deficiency causes the following sign and symptoms:
The child is restless, pale with flabby and toneless muscles which allow the limbs to assume unnatural postures.
Excessive sweating on the head is common.
Gastrointestinal upsets with diarrhoea is common.
The child/patient becomes prone to respiratory infections.
Development is delayed so that the teeth often erupt late and thre is failure to sit up.
The changes in bone are the most characteristic and easily identifiable signs of rickets.

Treatment:
A daily oral dose of 25-125 microgram of vitamin D cures rickets and osteomalacia. Advice on diet and general hygiene is needed. An adequate intake of calcium is essential. The best source source is milk and atleast 500 ml should be taken daily. An egg daily and butter or fortified margarine to increase the dietary intake of vitamin D are recommended. Children should enjoy playing in the sun.