Vitamin A
Way back in 1913, vitamin A was the first vitamin to be discovered. However, the importance of this vitamin had been well-known since the ancient Greeks. Hippocrates, the father of modern medicine, would tell his patients with failing eyesight to eat beef liver. Those who listened to him were usually able to see better, particularly at night. This famous physician did not know why liver helped the way it did, but today's health care practitioners know that animal liver is a very good source of vitamin A. These modern doctors also know the human body needs lots of vitamin A to properly function in the dark.
A lot more is known today about vitamin A: for instance, it aids in a wide range of bodily functions. These range from warding off cancer to keeping the skin smooth. Carotene is a natural type of vitamin A found in plant forms. Some of the carotenes in plant foods are turned into vitamin A and some go on to fight off free radicals that cause heart disease, cancer and other chronic problems.
Why People Need Vitamin A
When this vitamin was first discovered it was called the anti-infective agent. In studies with lab animals that were fed diets low in vegetables, fruits, and animal foods, they soon came down with eye infections. These infections cleared up as soon as proper foods were put back into their diets. This mysterious secret ingredient turned out to be fat-soluble vitamin A.
Vitamin A helps put up strong barriers to fight illness and infection. This vitamin accomplishes so much by helping the body's epithelial tissues (the cells that make up your skins and line the eyes, mouth, nose, throat, lungs, digestive tract and urinary tract) grow and repair themselves.
Without enough vitamin A the cells dry out and become stiff and do not work properly. Germs can then pass through the cells and into the body. Sometimes germs slip past these defenses even with enough vitamin A in the system, but this vitamin can help the immune system even after germs are in the body.
Vitamin A is also essential for healthy eyes. Teens and children need enough vitamin A to help them grow properly and build strong teeth and bones. However, even adults need vitamin A. The body is constantly replacing old, worn-out cells with new ones.
The human body needs carotenes even more than it needs vitamin A. In 1928 researchers discovered people could get vitamin A from eating plant foods that contained carotenes (the orange, red and yellow substances that give plants their colors). Beta carotene is the most abundant of the carotenes. The body converts beta carotene to vitamin A in the small intestine.
If a person does not happen to need vitamin A when they consume a food containing carotenes, it is not converted. Instead, the carotene circulates in the blood and enters the cells, storing it up in the fatty tissues. When extra vitamin A is needed, the liver converts this stored beta carotene.
Vitamin A Requirements
Anyone eating a typical diet will consume some of their vitamin A from meat, eggs and milk. The rest can be received in the form of carotenes (mostly beta) from vegetables and fruits. When a physician tells a patient how much vitamin A they should be getting, they assume some of the A will be in the form of beta carotene.
Because vitamin A is an essential nutrient it has an established RDA. Beta carotene is equally important but it does not have an RDA. Some researchers believe a healthy amount of vitamin A daily would be about 16,500 IUs, or 30 mg a day.
Caution should be used when taking supplements as vitamin A in large doses can be toxic. Symptoms of vitamin A overload include bone pain, headaches, blurred vision, diarrhea, loss of appetite, peeling and scaling skin and muscular weakness.
When the Body is Deficient
In modern areas it is rare for a real vitamin A deficiency to be present. However, some people fall into various categories that increase their risk for inadequate levels of this vitamin and include:
- Those who are vegetarians or vegans.
- People who have liver disease, cystic fibrosis, or even chronic diarrhea.
- Alcohol abusers. Alcohol tends to reduce the vitamin A and beta carotene in the body. This combination can also damage the liver.
- People who smoke cigarettes have low beta carotene levels.
- Women who take birth control pills. The pill raises the amount of vitamin A in the bloodstream but reduces the amount of this vitamin that is stored in the liver.
- Those who have chronic infections or are sick. Being ill makes the body produce more free radicals, which lowers the level of vitamin A.
- Individuals who are under a lot of stress (physical or psychological). Fatigue, overwork and even too much exercise can create free radicals, which lower the levels of vitamin A.
Symptoms of Vitamin B Deficiencies
One of the first symptoms of a vitamin A deficiency is night blindness and other eye problems. Vitamin A deficiencies can cause respiratory infections, sinus and ear infections, and sore throats. A condition called follicular hyperkeratosis can also occur, in which the skin starts to make too much of a hard protein called keratin. The skin starts to have small deposits of keratin that look like goosebumps. Reproductive problems can arise in both men and women.
Foods Containing Vitamin B
Vitamin A can be found in eggs, poultry, liver, milk and other dairy products. Nutritionists recommend getting beta carotene through five daily servings of fruits and vegetables. Again, the adage "having a lot of color on your plate" will net a good amount of beta carotene.
For those who choose supplements, vitamin A comes in soft gelcaps. Many people get their vitamin A from cod-liver oil.
References
- Alan H. Pressman and Sheila Buff.(2007). The Complete Idiot's guide to vitamins and minerals. New York : Alpha Books
- Brewer, S. (2010). The essential guide to vitamins, minerals and herbal supplements. London : Right Way
- Elson M. Haas, Md & Buck Levin, Phd, Rd.(2006). Staying Healthy with Nutrition: The Complete Guide to diet and nutritional medicine. Berkeley, Calif. : Celestial Art
- Holford, P. (2004). The optimum nutrition bible. London : Piatkus
- Holford, P & Lawson, S.(2008). Optimum Nutrition Made Easy How to achieve optimum health. London : Piatkus
- Lieberman, S. & Bruning, N. (2003). The Real Vitamin & Mineral Book. New York : Avery
- Rodale Health Books.(2009). Healing with vitamins : the best nutrients to slow, stop, and reverse disease. Emmaus, Pa. : Rodale
- Royston, A.(2003). Vitamins and minerals for a healthy body. Oxford : Heinemann Library
- The National Research Council.(1989). Recommended Dietary Allowances, 10th ed, National Academy of Sciences
- Werbach, M. (1993). Nutritional Influences on Illness. 2nd ed. Los Angeles: Third Line Press
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