2. Vitamins are very important for live.It is also very important for every one to live,but we need it in small amounts. There are several types of vitamins such as: A,B,C,D,K. So we will talk about every kind.

3. Functions : 1-Vision: Released all-trans retinol is converted to all- trans retinol,which can be transported across the inter photoreceptor matrix to the retinal epithelial cell to complete the visual cycle. Inadequate retinal available to the retina results in impaired dark adaptation known as ‘Night blindness’.

4. 2-Gene expression: Vitamin A,thyroid hormone and vitamin D may interact to influence gene transcription. Through the stimulation and inhibition of transcription of specific genes, retinoic acid plays a major role in cellular differentiation,the specialization of cells for highly physiological roles.Most of the physiological effects attributed to vitamin A appear to result from its role in cellular differentiation.

5. 3-IMMUNITY: (RA) play a central role in the development and differentiation of white blood cells,such as lymphocytes that play critical roles in the immune response. Activation of T-lymphocytes,the major regulatory cells of the immune system,appears to require all- trans (RA) binding of RAR. Vitamin A and retinoic acid

6. 4-Growth and development: Both vitamin A excess and deficiency are known to cause birth defects.Retinol and retinoic acid (RA) are essential for embryonic development.During fetal development,RA functions in limb development and formation of the heart,eyes,and ears.Additionally,RA has been found to regulate expression of the gene for growth hormone.

7. 5-Red blood cell production: Red blood cells,like all blood cells,are derived from precursor cells called stem cells.These stem cells are dependent on retinoids for normal differentiation into red blood cells.Additionally,vitamin A appears to facilitate the mobilization of iron from storage sites to the developing red blood cell for incorporation into hemoglobin,the oxygen carrier in red blood cells.

8. 6-Nutrient Interactions: *Zinc and vitamin A: Zinc deficiency is thought to interfere with vitamin A metabolism in several ways.Zinc deficiency results in decreased synthesis of retinol binding protein(RBP),which transports retinol through the circulation to tissues (e.g.,the retina).Zinc deficiency results in decreased activity of the enzyme that releases retinol from its storage form,retinyl palmitate,in the liver.Zinc is required for the enzyme that converts retinol into retinal.At present,the health consequences of zinc deficiency on vitamin A nutritional status in humans are unclear.

9. *Iron and vitamin A: Vitamin A deficiency may exacerbate iron deficiency(Anemia).Vitamin A supplementation has been shown to have beneficial effects on iron deficiency anemia and improve iron nutritional status among children and pregnant women.The combination of vitamin A and iron seems to reduce anemia more effectively than either iron or vitamin A alone.

10. Deficiency: Vitamin A deficiency and vision: Vitamin A deficiency among children in developing nations is the leading preventable cause of blindness.The earliest evidence of vitamin A deficiency is impaired dark adaptation or night blindness.Mild vitamin A deficiency may result in changes in the conjunctiva (Corner of the eye) called Bitot`s spots.Severe or prolonged vitamin A deficiency causes a condition called exophthalmia (Dry eye),characterized by changes in the cells of the cornea (Clear covering of the eye) that ultimately result in corneal ulcers,scarring,and blindness.

11. Vitamin A deficiency and infectious disease: Infection stimulates a vicious cycle,because inadequate vitamin A nutritional status is related to increased severity and likelihood of death from infectious disease.

12. Sources Free retinol is not generally found in foods.Retinyl palmitate,a precursor and storage form of retinol, is found in foods from animals. Plants contain carotenoids, some of which are precursors for vitamin A (e.g.,Alpha-carotene and B- carotene).Yellow and orange vegetables contain significant quantities of carotenoids. Green vegetables also contain carotenoids, though the pigment is masked by the green pigment of chlorophyll.Some of those foods are: Cod liver oil,fortified cereal,egg,butter,whole milk,sweet potato,carrot,cantaloupe,spinach,apricot,squash butternut and zucchini,summer.