E,xcessive intake of fat can lead to overweight and obesity MJCRONUTRIENTS VITAMINS Vitamins are organic compounds which are found in small amounts in food. TI1ey cannot be synthesized (except vitamin D) in the body and have specific and vital functions in cells irnc J tissues. Vitamins function in regulating the synthesis of many body tissues, participate in cellular metabolism as coenzymes and cofactors, involved synthesis of gene-cnntaining 1m1terials a. nd may function its antioxic Jan1s. Vitamins are classified into lwo groups according to their solubility in c. ither organic solvents (fat­ soluble) or water (waler-soluble). Fat soluble vitamins are stored i11 lhe body whil. e water solul Jle vitamins are generally not stored in significant amounts and are readily e,xcreled. Fat-soluble Vitamins Vitamin A 111ere arc two main forms or vitamin A. iu food: the prefonne<l vitamin A (retinol) or the vitamin itself :ind the precursor 01· pro-viti1min A (carotenes and simila. r substances). The nrnin function of vitamin A is i Ls role in vision since it is an essential component of rhodopsi. n (visual purple). It is also needed to maintain the integrity of epithelial tissues. Vitamin A is also needed for hone growth, immune system and reproduct ion. Prcformecl vitamin A is found in animal soun:es such as liver, milk, and eggs. Precursors (carotenes) nre found in dark green leafy vegetables and deep orange fruits and vegetables. Vitamin A deficiency is the main causeofprevenlablenutritioual blindnessamongyoung children. Clinical signs associated with the deficiency range from nightblinclness to keratomalacia (severe lesion}. Vitamin A deficiency is also associated with keratinfaation of the epitl1elial cells, depressed immune response, poor dental health and growth. On tl1e other hand, because it can be stored iu the body chronic excessive intakes can cause hypervitaminosis A or toxicity. Vitamin D The two most important forms of vitamin D in man are: vitamin D~!2 (ergocalciferol) found i. n plants and vitamin D-3(cholecal ciferol) found in animal tissues. Both vitamins are formed by ultraviolet irradiation. Cholecalciferol is found in eggs, butter, liver and cheese. A cholesterol-related vitamin D found in the sldn is converted to the active form of Lhe vitamin when exposed to sm:ilight. Vitamin Dis needed int. he absorption of calcium and phosphorus, it is needed in l>one formation, cellufar differentiation and modulates immune function. Deficiency of vitamin D can lead t bone,deformities called rickets, malabsorption syndrome, diseases of the liver and l..~dney. These can be prevented by exposure to sunlight, consumption of fortified foods and fish including its liver. Vitamin E Vitamin E exists in at least eight tocopherol and tocotrienol forms of which d-alpha tocopherol is the most widely distributed and has the highest biological activity. The richest dietary sources of vitamin E are the polyunsaturated vegetable oils and nuts. Vitamin E functions in the body as tissue antioxidant protecting liquid membrane of cells from oxidant damage. In food, it acts as an antioxidant by preventing the oxidation and breakdown of polyunsaturated fats. 329---