Vitamin D

Vitamin D





This vitamin was discovered in 1922. It is known as the antirachitic vitamin and

chemically as calciferol.





Sources of vitamin D. Vitamin D is found in fatty foods such as.small fish that are eaten whole,

liver, sardines, herrings, shark, salmon, butter, cheese, eggs, milk and palm oil (Fig. 8.2). A non-

food source of vitamin D is sunlight, for the action of sunlight on the skin changes the

cholesterol in the skin to vitamin D. In tropical countries this is a very valuable source of vitamin

D, as food containing vitamin D may not be eaten regularly. Daily requirements

Adults 400-800 International Units.

Children 300 International Units.





Stability and absorption of vitamin D. Vitamin D is very stable to heat and can

withstand normal periods of cooking and storage. Bile salts are necessary for the absorption of

this vitamin and fat absorption must be normal. Absorption is through the lacteals of the villi.

Excess vitamin D is stored in the liver.







Functions of vitamin D



1. It is required for the absorption and utilisation of calcium and phosphorus.



2. It helps in the regulation of the calcium and phosphorus levels in the blood.



3. It is associated with the growth and development of bones and teeth.







Deficiency of vitamin D





This leads to rickets, which is characterised by weakness and deformity of the bones. Lack of

other nutrients may also be responsible for this condition. Rickets generally occurs between the

sixth month to the second year of life, during the weaning period.

On examining the skull bones of a rachitic child, depressions will be seen along the sutures,

the forehead is prominent, and the anterior fontanelle remains wide open long after it should

have closed, at the eighteenth month of life. These abnormalities give the head the general

appearance of a box. The chest is narrow and deformed because the ribs are forced to curve

inwards through muscle action. In addition, the ribs have a beaded appearance due to

enlargement of the costochondral points.

The long limbs curve as soon as they start to bear weight when the child learns to walk. The

lower limbs may take the shape of a bow and sufferers are often referred to as having 'bow legs'

or 'bandy legs'. However, the child's legs may take up the opposite shape, so that his knees knock

together when he walks, and he is then described as having 'knock knees' (Fig. 8.3). Also,

abnormal enlargements can be found at the epiphyses; these are prominent at the wrist and ankle

joints. The vertebral column may curve, causing kyphosis or a 'hunch back'. Primary dentition is

delayed.