Dr.ehab fat soluble vitamins

Fat Soluble Vitamins

A, D, E and K

Vitamins may be defined as organic compounds occurring in small quantities in different natural foods and necessary for growth and maintenance of good health

Vitamins are essential food factors, which are required for the proper utilization of the proximate principles of food like carbohydrates, lipids and proteins

The vitamins are mainly classified into two: 1. The fat soluble vitamins are A, D, E and K 2, Water soluble vitamins are B complex and C, The major differences between these two groups

VITAMIN A

1. Chemistry

Vitamin A is fat soluble. The active form is present only in animal tissues. The pro-vitamin, beta-carotene is present in plant tissues. One molecule of beta-carotene can theoretically give rise to two molecules of vitamin A. Three different compounds with vitamin A activity are retinol (vitamin A alcohol), retinal (vitamin A aldehyde) and retinoic acid

Biochemical Functions of Vitamin A

vitamin D is called the "sun-shine vitamin".

As sunshine is less in winter months, vitamin deficiency is seen in winter

Deficiency of Vitamin D

The deficiency diseases are rickets in children and osteomalacia in adults. Hence vitamin D is known as antirachitic vitamin.

A. Causes for Vitamin D Deficiency

Clinical Features of Rickets

Clinical Features of Osteomalacia

Requirements of Vitamin D

VITAMIN E alpha tocopherol

Biochemical Role of Vitamin E

Vitamin E is the most powerful natural antioxidant

The free radicals would attack biomembranes. Vitamin E protects RBC from hemolysis.

It reduces the risk of myocardial infarction by reducing oxidation of LDL

Selenium is present in glutathione peroxidase; an important enzyme that oxidizes and destroys the free radicals. Selenium has been found to decrease the requirement of vitamin E and vice versa. They act synergistically to minimize lipid peroxidation.

Deficiency Manifestations of Vitamin E

vitamin E deficiency has been shown to produce muscular weakness

VITAMIN K They are naphthoquinone derivatives

Biochemical Role of Vitamin K

Vitamin K is necessary for coagulation factors such as Factor II (prothrombin) and Factor IX (Christmas factor)

These factors are synthesized by the liver as inactive zymogens. They undergo gamma carboxylation of glutamic acid residues. These are the binding sites for calcium ions. The gamma carboxyglutamic acid (GCG) synthesis requires vitamin K as a cofactor.

Causes for Deficiency of Vitamin K

deficiency can occur in conditions of malabsorption of lipids. This can result from obstructive jaundice. Prolonged antibiotic therapy and gastrointestinal infections with diarrhea will destroy the bacterial flora and can also lead to vitamin K deficiency.

Clinical Manifestations of Deficiency

Vitamin K deficiency is manifested as bleeding, especially internal bleeding. Very minor injuries will go on bleeding, as effective clot formation is lacking.

Prolongation of prothrombin time and delayed clotting time are characteristic of vitamin K deficiency. iii. Hemorrhagic disease of the newborn is attributed to vitamin K deficiency. It is often advised that pre-term infants be given prophylactic doses of vitamin K (1 mg Menadione). iv Warfarin and dicoumarol will competitively inhibit the gamma carboxylation system due to structural similarity with vitamin K. Hence they are widely used as anticoagulants for therapeutic purposes.

Daily Requirements of Vitamin K

Recommended daily allowance is 50-100 microgram/day. This is usually available in a normal diet.

Sources of Vitamin K

Green leafy vegetables are good dietary sources. Even if the diet does not contain the vitamin, intestinal bacterial synthesis will meet the daily requirements, as long as absorption is normal.