Nutrition Vitamin A

What is it? The term vitamin A is used to describe all substances that result in vitamin A activity in biologic systems. Thisincludes retinol, retinoic acid, and retinyl esters (such as the retinyl-palmitate, found in vitamin capsules.) What does it do? A form of vitamin A called retinal forms some of the light-sensitive pigment in the retina of the eye. It helps certain tissues develop normally both in the embryo and in adults. (Too much, in fact, causes developmental abnormalities, too.) While important to the function of most tissues in the body, vitamin A is especially important for the skin, reproduction and the immune system. It retards the formation of certain cancers. (See the Lancet January 7, 1995 for an overview.) Which form of vitamin A is best? It is best to eat a diet that provides all the vitamin Aactivity you need. Your daily requirement ofvitamin A can be obtained from the carotene in aserving of sweet potato, carrot, spinach, pumpkin,collard greens, broccoli, watermelon, cantaloupe,apricots, nectarine, and many other foods. VitaminA is present in liver and other animal foods.Vitamin A is stored in the body for a long time, soyou could eat a big piece of liver once a week andyou�d have all the vitamin A you needed.(Assuming you like liver. I�ll take the pumpkin pie.) Some vegetables are yellow and orange because they contain carotene. In the body, carotene is transformed into vitamin A as needed. To provide extra vitamin A activity, a doctor may prescribe either vitamin A or beta-carotene. Vitamin A is much less expensive but there is the risk of overdose. One cannot overdose on beta-carotene but it is more difficult to absorb and it�s about five times as costly. Also, your body may not make enough vitamin A from beta-carotene to correct every vitamin A-responsive condition. Why take vitamin A? Vitamin A helps maintain a healthful skin, bones,teeth and gums. It is required for good night vision. Self care with vitamin A Because vitamin A can be toxic in excessiveamounts, I don�t recommend vitamin A use withoutthe advice of someone familiar with your healthsituation. To inspire you to eat a diet rich invegetables with vitamin A in it, let me tell you thatintake of vitamin A has been shown to be protectiveagainst cancer of the mouth, cervix and breast.Communities in which vitamin A supplements aregiven to all the children have a significant reductionin mortality among those children. Studies showthat people with an acute infection have anincreased need for vitamin A. Prevention with Vitamin A A study in Belgium found that people with higherlevels of vitamin A in the blood recovered morequickly and completely from stroke ( Lancet1992;339:1562). The British Medical Journalreported that elderly people with higher levels ofvitamin A had an enhanced immune response.Adequate intake of vitamin A can help preventcancer of the cervix (Nutrition and Cancer1984;6:49), cancer of the head and neck (Eur ArchOtolaryngol 1990; 247:368), cancer of the prostate(Cancer Research 1990; 50:2311), high bloodpressure (Science 1984 224;1392), upperrespiratory infection in children (Aust Paediatr J1986;22:95), and age-related macular degeneration(American Journal of Epidemiology 1988;128:700). Medical use of vitamin A Vitamin A should not be used to treat medicalconditions without the advice of your physician.However, you should know that vitamin A has anantiviral effect and can strengthen the immunesystem. Researc h has shown benefits from VitaminA for many medical conditions, including excessivemenstrual flow, delayed wound healing, rheumatoidarthritis, loss of night vision, loss of hearing,anemia, hypertension, measles, chronic sinusitis,fibrocystic breast disease, increased tendency toform calluses, retinitis pigmentosa, acne, psoriasis,and many other skin diseases. Vitamin A wasshown to improve response to chemotherapy inwomen with breast cancer. Vitamin A deficiency People who do not eat the proper kind of food cansuffer vitamin A deficiency. We must be able toabsorb fat in order to absorb vitamin A (and betacarotene),else we can be vitamin A deficient evenwhile taking the best vitamin A supplement. Alsopeople who are deficient in vitamin E or zinc orwho have liver disease can fail to absorb vitamin A. Vitamin A can be toxic in large doses Adults can develop symptoms from doses in excessof 50,000 I.U. per day for a period of several years.An 18 year study of 72,000 post-menopausalwomen revealed more fractures in those womenwho had diets highest in vitamin A (includingsupplements). Those using estrogen did not suffermore fractures. See our July 2002 newsletter formore details. Smaller doses might be harmful inpeople with liver disease or malnutrition. Signs oftoxicity include dry, cracked skin, brittle nails, lossof hair, headache, muscle ache, irritability, fatigueand nausea. These signs disappear when thevitamin is discontinued. Children are more susceptible to vitamin A toxicityas they are smaller in size and might accidentallytake vitamin A supplements meant for adults. Asingle dose of 100,000-300,000 units in a childcould cause vomiting, severe headache and lethargy.Symptoms generally resolve quickly once the childstops taking the vitamin A and complete recovery isgenerally the rule. However, vitamin A (as anysupplement) must be kept out of the reach ofchildren. Optimal dose of vitamin A As noted above, just one serving a day of carotenerichvegetables and fruits will provide you with therecommended daily allowance.In a group of people studied at the University ofAlabama, those who consumed about 6,600 IU ofvitamin A a day from food and supplementsappeared to live the longest. However, women whoconsume more than 5000 units a day seem toincrease their risk of hip fracture, at least on theaverage. Our newsletter points out that there maybe some trade-offs between longevity and bonestrength. Adults can reasonably and safely take an extra100,000 units a day for a week to help end a cold orupper respiratory tract infection. If vitamin Adoesn�t appear to help your problem, you may notbe absorbing it. Take pancreatic enzymes with eachdose to enhance absorption. The current recommended maximum intake forpregnant women and women who might becomepregnant is 10,000 units of vitamin A per day.Higher doses may increase the risk of birth defects.

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