Anonymous
Anonymous asked in HealthOther - Health · 1 decade ago

deficiency of vitamin A,the various kinds incl. xerophthalmia,follicular keratosis,xerophthalmia,bitot spots..

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  • 1 decade ago
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    Vitamin A deficiency exists when the chronic failure to eat sufficient amounts of vitamin A or beta-carotene results in levels of blood-serum vitamin A that are below a defined range. Beta-carotene is a form of pre-vitamin A, which is readily converted to vitamin A in the body. Night blindness is the first symptom of vitamin A deficiency. Prolonged and severe vitamin A deficiency can produce total and irreversible blindness.

    Vitamin A (called retinol in mammals) is a fat-soluble vitamin. The recommended dietary allowance (RDA) for vitamin A is 1.0 mg/day for the adult man and 0.8 mg/day for the adult woman. Since beta-carotene is converted to vitamin A in the body, the body's requirement for vitamin A can be supplied entirely by beta-carotene. Six mg of beta-carotene are considered to be the equivalent of 1 mg of vitamin A. The best sources of vitamin A are eggs, milk, butter, liver, and fish, such as herring, sardines, and tuna. Beef is a poor source of vitamin A. Plants do not contain vitamin A, but they do contain beta-carotene and other carotenoids. The best sources of beta-carotene are dark-green, orange, and yellow vegetables; spinach, carrots, oranges, and sweet potatoes are excellent examples. Cereals are poor sources of beta-carotene.

    Vitamin A is used for two functions in the body. Used in the eye, it is a component of the eye's light-sensitive parts, containing rods and cones, that allow for night-vision or for seeing in dim-light circumstances. Vitamin A (retinol) occurs in the rods. Another form of Vitamin A, retinoic acid, is used in the body for regulating the development of various tissues, such as the cells of the skin, and the lining of the lungs and intestines. Vitamin A is important during embryological development, since, without vitamin A, the fertilized egg cannot develop into a fetus.

    Vitamin A deficiency occurs with the chronic consumption of diets that are deficient in both vitamin A and beta-carotene. When vitamin A deficiency exists in the developed world, it tends to happen in alcoholics or in people with diseases that affect the intestine's ability to absorb fat. Examples of such diseases are celiac disease (chronic nutritional disorder), cystic fibrosis, and cholestasis (bile-flow failure or interference). Vitamin A deficiency occurred in infants during the early 1900s in Denmark. The deficiency resulted when milk fat was made into butter for export, leaving the by-product (skimmed milk) for infant feeding. Vitamin A deficiency has taken place in infants in impoverished populations in India, where the only foods fed to the infants were low in beta-carotene. Vitamin A deficiency is also common in areas like Southeast Asia, where polished rice, which lacks the vitamin, is a major part of the diet.

    The earliest symptom of vitamin A deficiency is night blindness. Prolonged deficiency results in drying of the conjunctiva (the mucous membrane that lines the inner surface of the eyelids and extends over the forepart of the eyeball). With continued vitamin A deficiency, the drying extends to the cornea (xerophthalamia). The cornea eventually shrivels up and becomes ulcerated (keratinomalacia). Superficial, foamy gray triangular spots may appear in the white of the eye (Bitot's spots). Finally, inflammation and infection occur in the interior of the eye, resulting in total and irreversible blindness.

    Vitamin A status is measured by tests for retinol. Blood-serum retinol concentrations of 30-60 mg/dl are considered in the normal range. Levels that fall below this range indicate vitamin A deficiency. Night blindness is measured by a technique called electroretinography. Xerophthalamia, keratinomalacia, and Bitot's spots are diagnosed visually by trained medical personnel.

    Vitamin A deficiency can be prevented or treated by taking vitamin supplements or by getting injections of the vitamin. The specific doses given are oral retinyl palmitate (110 mg), retinyl acetate (66 mg), or injected retinyl palmitate (55 mg) administered on each of two successive days, and once a few weeks later if symptoms are not relieved.

    The prognosis for correcting night blindness is excellent. Xerophthalamia can be corrected with vitamin A therapy. Ulcerations, tissue death, and total blindness, caused by severe vitamin A deficiency, cannot be treated with vitamin A.

    Vitamin A deficiency can be prevented by including foods rich in vitamin A or beta-carotene as a regular component of the diet; liver, meat, eggs, milk, and dairy products are examples. Foods rich in beta-carotene include red peppers, carrots, pumpkins, as well as those just mentioned. Margarine is rich in beta-carotene, because this chemical is used as a coloring agent in margarine production. In Africa, Indonesia, and the Philippines, vitamin A deficiency is prevented by public health programs that supply children with injections of the vitamin.

    Key Terms

    Bitot's spots

    Bitot's spots are superficial, foamy gray, triangular spots on the white of the eyeball.

    Carotenoids

    Carotenoids are yellow to deep-red pigments.

    Conjunctiva

    The conjunctiva is a clear layer of cells that covers the eye and directly contacts the atmosphere. The conjunctiva is about five-cells thick.

    Cornea

    The cornea is a clear layer of cells that covers the eye, just under the conjunctiva. The cornea is about 50-cells thick.

    Fat-soluble vitamin

    Fat-soluble vitamins can be dissolved in oil or in melted fat.

    Water-soluble vitamins can be dissolved in water or juice.

    Keratinomalacia

    Keratinomalacia is ulceration of the cornea.

    Recommended Dietary Allowance (RDA)

    The Recommended Dietary Allowances are quantities of nutrients in the diet that are required to maintain good health in people. RDAs are established by the Food and Nutrition Board of the National Academy of Sciences, and may be revised every few years. A separate RDA value exists for each nutrient. The RDA values refer to the amount of nutrient expected to maintain good health in people. The actual amounts of each nutrient required to maintain good health in specific individuals differ from person to person.

    Xerophthalmia

    Xerophthalmia is a dry, thickened, lusterless condition of the eyeball resulting from vitamin A deficiency.

    For Your Information

    Books

    Brody, T. Nutritional Biochemistry. San Diego: Academic Press, Inc., 1998.

    Combs, G. The Vitamins. San Diego: Academic Press, Inc., 1992.

    Food and Nutrition Board. Recommended Dietary Allowances. 10th ed. Washington, DC: National Academy Press, 1989.

    Periodicals

    Filteau, S. M., and A. M. Tomkins."Vitamin A Supplementation in Developing Countries." Archives of Disease in Childhood 72 (1995): 106-109.

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  • Anonymous
    4 years ago

    In a strange way the "Loss of Sense of Humour" can be caused by lack of strong sunlight in the eyes. Serotonin levels can be elevated by increased exposure to light, according to Greg Danzig, president of lonair Co. "Light and antidepressants like Prozac help. But researchers say negative ions may also increase brain levels of serotonin." It usually happens during the winter. A less common type of SAD ("Seasonal Affective Disorder" Also called: Seasonal depression, Seasonal mood disorder) happens in the summer. Food for the mood is the rule, eat more fruits and vegetables and less fat and sweets to stabilize moodiness, according to Delicious On-line, an Internet magazine. Magnesium, vitamin B6, Vitamin C, and folic acid are additives you may also want to consider . Excessive intake of alcohol, caffeine and nicotine and added stress, are also discouraged if you are affected by the wintertime depression. Daily walks or exercise routines are encouraged. This is but one of several reasons... Did you know that the U.S.D.A.'s "Recommended Dietary Allowance" for vitamins and minerals was to keep you from getting Scurvy and had nothing to do with maintaining good health? Did you know that you cannot survive on processed foods without a multi-vitamin these days as the soil is so depleated. Did you know that if the vitamins are not water soluible the body cannot use them, and most are not? ME! Mahatma Gamdhi as you know, walked barefoot most of the time, which produced an impressive set of calluses on his feet. He also ate very little, which made him rather frail and with his odd diet, he suffered from bad breath. This made him (oh, man, this is so bad, it's good) ... a super-calloused fragile mystic hexed by halitosis. .

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