Lipid soluble vitamins

 Vitamins A, D and K are all lipid soluble.
1. Vitamin A
The natural form was first recognised in 1920 and can be synthesised under artificial conditions. It is found in two forms in food.

• Vitamin A form (liver, fish oil, butter, egg-white (albumin)).
•  Provitamin A form (plant sources).

2.  Provitamin A 

It is required together with vitamin E for normal growth of the body. Pumpkin, tangerine, orange, banana, plum, apricot, strawberry and most cereals all Contain rich sources of provitamin A. The liver Converts each molecule of provitamin A to two molecules of vitamin A. Vitamin A is present in blood and in all other cells. Excess vitamin A is stored in liver. Food that has been spoiled by bacteria for example, loses most of its vitamin A content. 

It participates to the structure of eye pigments. Its deficiency results in disorders such as night blindness and in-flammation of the eye. Individuals suffering from deficiency symptoms can not differentiate between the colors blue and yellow in daylight. Excess vitamin A produces some side effects such as weight loss, hair loss, exhaustion, lack of appetite and serious disorders in body organs such as the heart, kidney and liver, where it causes degeneration of liver cells. An excess of this vitamin also causes fragile bones and teeth. 

3. Vitamin D 

It Was first discovered in 1906 as the cause of rickets, a bone disorder. Sunlight initiates the formation of vitamin D from its precursors under the skin. In the last decade, synthetic forms of this vitamin have become available. In its natural state, it is found in fish oil and other animal foodstuffs such as offal and milk.

The requirement for vitamin D increases during growth and pregnancy. 

Excess amounts during infancy cause vomiting, lack of appetite, dry skin, thirst, high blood pressure and disorders in smooth tissues. Additionally the individual may become paralysed. In adults, any excess vitamin D is stored in the liver. 

Deficiency of vitamin D disrupts the calcium/phosphate balance and results in deformities in bones and teeth, a disorder known as rickets. Children showing symptoms of rickets have a deformed rib cage resembling that of a chicken and also have bandy legs. 

4. Vitamin E 

It Was first discovered in 1922 when its structure was formulated. It is heat resistant, but is destroyed on exposure to air and ultraviolet light. It is however, unaffected by boiling. A synthetic form of vitamin E is available.

A rich source of this vitamin is oil obtained from seeds. Other sources include cereal embryos, green vegetables, meat and milk. Excess vitamin E is deposited in muscles. Its deficiency is rare but when present may cause infertility. It facilitates fertilisation and growth of the placenta. It also promotes the growth of the testes and ovaries. Addi-tionally, it works in combination with vitamin A in the growth of an organism. Poultry feed is enriched with vitamin E since it is effective in rapid growth and prolongs the shelf life of chicken meat.

5. Vitamin K

It was first discovered in 1929 and its structure was formulated. It is destroyed on exposure to sunlight. The natural form of this vitamin can only be absorbed in the presence of bile. Synthetic forms of this vitamin however, do not require bile for absorption.
It is abundant in green vegetables, fish, milk and meat and is also present in other foodstuffs. It is synthesised in the large intestine by the bacterial flora and is stored in the liver. Vitamin K promotes the formation ofprothrombin, effective in blood clotting. In the deficiency of this vitamin, blood fails to clot. Any bleeding of newborn infants may cause serious problems since there is no reserve of this vitamin in the body and clotting can not occur.