Vitamin D is unique because it is derived both from sunlight and foods. Vitamin D is synthesized by the body by the action of UV rays of sunlight on 7-dehydroxycholesterol, which is stored in the skin in large amounts. Vitamin occurs in foods of animal origin. Liver, egg yolk, butter and cheese and some species of fish contain useful amounts of vitamin D. fish liver oil are the richest source of vitamin D. dietary sources of vitamin d are given below in the table
µ g/per 100g
Cod liver oil
Halibut liver oil
Shark liver oil
Benefits of vitamin D:
Vitamin d is needed in the development of strong, healthy bones. Its chief function is to maintain the right concentration of calcium and phosphorus in the body. Vitamin D is necessary for the calcification process. This is particularly important in babies and young children, whose bones develop comparatively at a faster rate. Vitamin D maintains normal structure of bones and assists to govern the balance between bone calcium and blood calcium. It also helps in the development of the normal teeth. In deficiency of vitamin D the formation of the teeth becomes defective and leads to the development of dental caries. Vitamin controls the retention of calcium and parathyroid regulates the level of blood calcium by controlling movement of calcium from the bones. Thus vitamin D and parathyroid help each other in calcium metabolism and bone formation. It lowers the pH in the colon, caecum, ileum, etc. and increases the urinary pH simultaneously. It also permits normal growth. On the whole the function of vitamin D is to cause increased absorption, longer retention and better utilization of calcium and phosphorus in the body.
Exogenous vitamin D is required throughout the period of skeletal growth, i.e. to adult life.
The recommendations for infants under 1 year are 400-800 i.u. daily, and for children and adolescents up to 20 years – 400 i.u.
In the latter half of pregnancy and throughout lactating period, the dose should be 400-800 i.u.
Deficiency symptoms of vitamin D:
The most important change in this vitamin deficiency is an increased loss of calcium and phosphate in the stools. This leads to a fall in their blood level and hence not available for bone formation. Due to this reason, the children suffer from rickets and adults from osteomalacia. Rickets occur in children between 6 and 18 months of life during the period of skeletal growth. The bones become soft and easily bent. Under the constant pull of the muscles, the joints lose their shape and are not able to function, as they should. The disease is characterized by growth failure, bone deformity, muscular hypotonia, tetany and convulsions due to hypo calcemia. In young infants there may be a marked softening of the bones of the skull. The head may be flattened on one side. Premature infants are more prone to have rickets. The danger is great to darker skinned children who live in cooler climates. Breast fed babies are more likely to develop rickets if the mother is not on a well balanced diet.
Osteomalacia is a form of adult ricket. It is due to deficiency of vitamin D and calcium in the diet. It occurs in women during pregnancy and lactation when a large amount of calcium is depleted from the mother.
In the absence of vitamin D there is decreased absorption of calcium from the food and also diminished the level of phosphate in blood.
In vitamin D deficiency, formation of cartilage is continued but in irregular fashion and calcification may stop completely.
Deficiency of vitamin D also leads to the development of dental caries.
Prevention measures include educating parents to expose their children regularly to sunshine, periodic dosing of vitamin D.
Vitamin D is stored in the body in fatty tissues and in the liver. An excessive intake is harmful and may result in anorexia, nausea, vomiting, thirst and drowsiness. The patient may lapse into coma, while cardiac and renal failure may occur. The effects are due to hypercalcaemia produced by increased intestinal absorption and mobilization of calcium from bone.