Fat soluble vitamins

The fat soluble vitamins are so called because they dissolve in fat and are absorbed along with fat.

Any condition which interferes with the absorption of fat can lead to deficiency of these vitamins.

They are stored in liver and in subcutaneous fat and the deficiency develops slowly unlike that of water soluble vitamins.

Because of this excess of these vitamins can cause problems as opposed to water soluble vitamins which are readily excreted from the body. There are four fat soluble vitamins called A, D, E and K.

Vitamin A: This term usually includes preformed vitamin called retinol and a pro-vitamin beta carotene which is converted to retinol in the intestine.

Sources: Vitamin A is found is green leafy vegetables, mango, papaya and carrots. Animal foods rich in vitamin A are liver, eggs, whole milk and fish.

Functions: Vitamin A plays a vital role in normal vision. It is indispensable for the formation of a pigment called rhodopsin which is necessary for vision in dim light. Hence its deficiency causes night blindness.

Vitamin A is essential for the integrity of the cells lining the intestines, urinary tract, respiratory tract and skin. Its deficiency causes dry and rough skin. Skeletal growth also requires vitamin A.

In more severe vitamin A deficiency there will be dryness of eyes (xerophthalmia). If not vigorously treated at this stage there can be perforation of cornea leading to irreversible blindness. Vitamin a deficiency has caused blindness in many children in developing countries.

Excess of vitamin A causes increased intracranial pressure, headache pain in muscle and joints.

Vitamin D: Vitamin D can be derived from foods as well as from the action of sunlight on the skin. The ultraviolet rays of skin act on 7- dehydrocholesterol which is normally present in human skin and convert it into inactive form of vitamin D. Foods which contain vitamin D are liver, egg yolk, butter and cheese.

Function: Vitamin D has to be transformed in the body to its metabolically active form. Both liver and kidney are responsible for this transformation. The final change takes place in the kidney resulting in the formation of 1, 25 dihydroxy-cholecalceferol- the active form of vitamin D. Parathyroid hormone activates the enzyme needed for transformation

The active form acts on the intestine to increase absorption of calcium and phosphorous. It also acts on the kidneys to increase re-absorption of calcium which is filtered into the Bowman’s capsule.

Excess of vitamin D can cause increased calcium in blood, constipation, vomiting and deposits of calcium in kidneys.

Deficiency of vitamin D occurs due to inadequate exposure to sunlight and low dietary intake. As its absorption is dependent on that of fat any fat malabsorption can lead to vitamin D deficiency. Renal disease can also cause vitamin D deficiency.

Vitamin D deficiency causes osteomalacia (softening of bones) in adults and rickets in children. Rickets causes bony deformities.

Vitamin E: The term Vitamin E refers to a group of compounds called tocopherols. The major tocopherols are alpha, beta, gamma and delta. Alpha tocopherol is the most active form biologically.

Vitamin E is an important antioxidant. It can donate an electron to a free radical to stop oxidation. We now know that antioxidants play a crucial role is preventing oxidative damage to cells. Decreased antioxidant activity leads to premature aging.

Vitamin E deficiency can occur in premature babies, liver diseases and pancreatic diseases. Its deficiency shortens life span of RBCS and leads to anemia.

Vitamin K: Vitamin K is synthesized in the intestine by the bacteria normally present there. It is necessary for maintaining normal levels of proteins involved in the clotting of blood.

The colonization of intestine by bacteria is delayed in babies who are exclusively breast fed. This can result in vitamin K deficiency and lead to a condition called hemorrhagic disease of newborn. Hence it is a routine practice to give one injection vitamin K to every newborn baby immediately after delivery.

Later in life vitamin K deficiency may occur in conditions causing fat mal-absorption.

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