Fat Soluble Vitamins A, D, E and KVitamins may be defined as organic compounds occurring in small quantities indifferent natural foods and necessary for growth and maintenance of good healthVitamins are essential food factors, which are required for the proper utilizationof the proximate principles of food like carbohydrates, lipids and proteinsThe vitamins are mainly classified into two:1. The fat soluble vitamins are A, D, E and K2, Water soluble vitamins are B complex and C, The major differences betweenthese two groups
VITAMIN A1. 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 RicketsClinical Features of Osteomalacia Requirements of Vitamin D
VITAMIN Ealpha tocopherolBiochemical Role of Vitamin EVitamin E is the most powerful natural antioxidantThe free radicals would attack biomembranes. Vitamin E protects RBC fromhemolysis.It reduces the risk of myocardial infarction by reducing oxidation of LDLSelenium is present in glutathione peroxidase; an important enzyme that oxidizesand destroys the free radicals. Selenium has been found to decrease therequirement of vitamin E and vice versa. They act synergistically to minimize lipidperoxidation.
Deficiency Manifestations of Vitamin Evitamin E deficiency has been shown to produce muscular weakness
VITAMIN KThey are naphthoquinone derivativesBiochemical Role of Vitamin KVitamin K is necessary for coagulation factors such as Factor II (prothrombin) and FactorIX (Christmas factor)These factors are synthesized by the liver as inactive zymogens. They undergo gammacarboxylation 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 Kdeficiency can occur in conditions of malabsorption of lipids. This can result fromobstructive jaundice. Prolonged antibiotic therapy and gastrointestinal infections withdiarrhea will destroy the bacterial flora and can also lead to vitamin K deficiency.Clinical Manifestations of DeficiencyVitamin K deficiency is manifested as bleeding, especially internal bleeding. Very minorinjuries will go on bleeding, as effective clot formation is lacking.
Prolongation of prothrombin time and delayed clotting time are characteristic ofvitamin K deficiency.iii. Hemorrhagic disease of the newborn is attributed to vitamin K deficiency. It is oftenadvised that pre-term infants be given prophylactic doses of vitamin K (1 mgMenadione).iv Warfarin and dicoumarol will competitively inhibit the gamma carboxylation systemdue to structural similarity with vitamin K. Hence they are widely used asanticoagulants for therapeutic purposes.
Daily Requirements of Vitamin KRecommended daily allowance is 50-100 microgram/day. This is usually available in anormal diet.Sources of Vitamin KGreen leafy vegetables are good dietary sources. Even if the diet does not contain thevitamin, intestinal bacterial synthesis will meet the daily requirements, as long asabsorption is normal.