(1) Rickets: Vitamin D deficiency leads to rickets, which is usually observed in young children between the age of six months and two years. There is reduced calcification of growing bones. The disease is characterized by growth failure, bone deformity, muscular hypotonia, tetany and convulsions due to hypo-calcemia. There is an elevated concentration of alkaline phosphates in the serum. The bony deformities include curved legs, deformed pelvis, pigeon chest, Harrison's sulcus, rickety rosary, kyphoscoliosis, etc. The milestones of development such as walking and teething are delayed.

(2) Osteomalcia: In adults, vitamin D deficiency may result in osteomalacia, which occurs mainly in women, especially during pregnancy and lactation when requirements of vitamin D are increased.

Both rickets and osteomalacia are frequently reported in India, although they do not appear to be a problem of public health importance. In the world as a whole, their prevalence has declined as a result of changes in social customs (e.g., purdah system), and the expansion of mother and children health services leading to better care and feeding of infants and children (3). In the developing countries today, rickets as a menace to child health is overshadowed by the prevalence of protein energy malnutrition.

Prevention: Preventive measures include

(a) Educating parents to expose their children regularly to sunshine; (b) Periodic dosing (prophylaxis) of young children with vitamin D; and vitamin D fortification of foods, especially milk. Some industrialized countries still carry out the last measure. Periodic dosing and education appear to be the most practical approaches in developing countries.

Fraser urges caution concerning oral supplementation, because orally administered vitamin D appears to bypass the protective mechanism the prevent excessive 25 (OH) D 3 formation. The margin of safety with oral vitamin D between the nutrient requirement and toxic intake is narrow. The signs of vitamin d toxicity are usually related to hypercalcemia, like thirst, anorexia, polyuria and the risk of metastic calcification.