Vitamin A is a fat-soluble vitamin that has several important functions in the body:
Vitamin A also helps keep skin and mucous membranes that line the nose, sinuses, and mouth healthy. It plays a role in immune system function, growth, bone formation, reproduction, and wound healing.
Vitamin A comes from two sources. One group comes from animal sources and is called retinoids, which includes retinol. The other group comes from plants and is called carotenoids, which includes beta-carotene. The body converts beta-carotene to vitamin A.
It' s rare to have a serious deficiency of vitamin A in the developed world. Symptoms include dry eyes, night blindness, diarrhea, and skin problems.
While vitamin A is essential for good health, it can be toxic in high doses. Never take more than the recommended daily allowance without first talking to your doctor.
Acne, Psoriasis, and other Skin disorders
Prescription creams and pills containing retinoids, a synthetic form of vitamin A, are used to help clear up severe acne and psoriasis and have shown promise for treating other skin disorders, premature aging from the sun and warts. These medications require close supervision by a doctor. Isotretinoin (Accutane), an oral medication for acne, can cause very serious side effects and must not be used by pregnant women or women of child-bearing age who are not taking some birth control.
Getting enough vitamin A in your diet is essential for good vision. Research shows that people who eat more foods with vitamin A are less likely to develop age-related macular degeneration. In addition, a large population study found that people who got high levels of vitamin A though their diets had a lower risk of developing cataracts. But researchers don' t know whether taking vitamin supplements would work the same way. Vitamin A supplements may help slightly slow down the damage from retinitis pigmentosa, a hereditary disease that causes poor night vision. The study used high doses, however, which can be toxic.
For children who have vitamin A deficiency, supplements can reduce the severity and complications of measles. Children who are deficient in vitamin A are more likely to develop infections, including measles. In areas of the world where vitamin A deficiency is widespread or where at least 1% of those with measles die, the World Health Organization recommends giving vitamin A supplements to children who have measles. However, vitamin A does not seem to help unless a child has vitamin A deficiency. Never give a child vitamin A supplements without a doctor's supervision.
Inflammatory Bowel Disease (IBD)
People with IBD, both ulcerative colitis and Crohn' s disease -- may have a hard time absorbing all the nutrients their bodies need. Health care providers often recommend that people with IBD take a multivitamin, including vitamin A.
Whether vitamin A can reduce the risk of cancer is not clear. People who eat a healthy diet with enough beta-carotene and other carotenoids from fruits and vegetables seem to have a lower risk of certain cancers, such as breast, colon, esophageal, and cervical cancer. And some laboratory studies suggest that vitamin A and carotenoids may help fight certain types of cancer in test tubes.
But there is no proof that taking vitamin A supplements will help prevent or treat cancer. In fact, there is some evidence that it may be harmful. Taking beta-carotene or vitamin A supplements has been linked to a higher risk of lung cancer in people who smoke or drink alcohol. However, some researchers say more studies are needed to confirm this.
One preliminary study suggests that a topical form of vitamin A may reduce abnormal growth of cells on the cervix, called cervical neoplasia.
Researchers are also investigating retinoids, a synthetic form of vitamin A, for skin cancer. People with certain types of skin cancer tend to have lower levels of vitamin A and beta-carotene in the blood. However, studies that have looked at whether taking higher amounts of vitamin A or beta-carotene would prevent or treat skin cancer have had mixed results.
Vitamin A, in the form of retinyl palmitate, is found in beef, calf, and chicken liver; eggs; fish liver oils; and dairy products, including whole milk, whole milk yogurt, whole milk cottage cheese, butter, and cheese.
The body can also make vitamin A from beta-carotene and other carotenoids, fat-soluble nutrients found in fruits and vegetables that give them their color. Most dark-green leafy vegetables and deep yellow/orange vegetables and fruits -- sweet potatoes, carrots, pumpkin and other winter squashes, cantaloupe, apricots, peaches, and mangoes -- contain substantial amounts of beta-carotene. By eating these beta-carotene rich foods, you can increase levels of vitamin A in your body.
Vitamin A supplements are available as either retinol or retinyl palmitate.
Tablets or capsules are available in a variety of doses. The tolerable upper limit, or safe upper limit, is 10,000 IU. For any dose close to that amount, a doctor should help you determine the amount to take. Most multivitamins contain the recommended dietary allowance (RDA) for vitamin A (see "How To Take It").
Unlike vitamin A, beta-carotene does not build up in the body. However, there is some evidence that high doses of beta-carotene can carry some risk. Talk to your doctor before taking more than the recommended amount.
Vitamin A is absorbed along with fat in the diet. Take it with food.
Studies often use high doses of vitamin A. However, such high doses can be toxic. A health care provider should monitor any high-dose therapy (more than 10,000 IU for an adult, or above the recommended daily allowance for a child).
Daily dietary intakes for vitamin A are:
Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.
Taking too much vitamin A when you are pregnant can cause serious birth defects. Because all prenatal vitamins contain some vitamin A, you shouldn' t take a separate vitamin A supplement.
Synthetic vitamin A can cause birth defects. Women who are pregnant or trying to become pregnant shouldn' t take this form if vitamin A.
Too much vitamin A is toxic and can cause liver failure, even death. Symptoms of vitamin A toxicity include lasting headache, fatigue, muscle and joint pain, dry skin and lips, dry or irritated eyes, nausea or diarrhea, and hair loss. Vitamin A from foods is considered safe, but you can get too much from supplements. For adults 19 and older, the tolerable upper limit for vitamin A is 10,000 IU per day. Talk to your doctor before taking any dose close to that amount.
People who have liver disease or diabetes should not take vitamin A supplements without their doctor' s supervision.
Smokers and people who drink heavy amounts of alcohol should not take beta-carotene supplements.
Both vitamin A and beta-carotene may increase triglycerides, which are fats in the blood. They may even increase risk of death from heart disease, particularly in smokers.
Vitamin A is found in many different types of vitamin formulas. Supplements that say "wellness formula," "immune system formula," "cold formula," "eye health formula," "healthy skin formula," or "acne formula," all tend to contain vitamin A. If you take a variety of different formulas, you could be at risk for too much vitamin A.
If you take large doses of vitamin A, you may want to avoid the food carob. It increases the amount of vitamin A available in your body.
If you are being treated with any of the following medications, you should not use vitamin A without first talking to your health care provider:
Tetracycline antibiotics -- People who take a type of antibiotics called tetracyclines and also take high doses of vitamin A may be at risk for a condition called intracranial hypertension, a rise in the pressure of brain fluid. Tetracyclines include:
Antacids -- One study suggests that the combination of vitamin A and antacids may be more effective than antacids alone in healing ulcers.
Anticoagulants (blood thinners) -- Long-term use of vitamin A or taking high doses may increase the risk of bleeding for those taking blood-thinning medications, particularly warfarin (Coumadin). Talk to your doctor before taking vitamin A.
Cholesterol-lowering medications (bile acid sequestrants) -- The medications cholestyramine (Questram) and colestipol (Colestid) may reduce the body's ability to absorb vitamin A and lead to lower levels in the body. A water-soluble form of vitamin A may help. Another class of cholesterol-lowering medications called statins may actually raise vitamin A levels in the blood.
Doxorubicin -- Test tube studies suggest that vitamin A may make the action of doxorubicin, a medication used to treat cancer, stronger. More research is needed to understand the effect. If you are undergoing treatment for cancer, ask your oncologist before taking vitamin A or any supplement.
Medications processed by the liver --Taking high doses of vitamin A along with some other medications that are processed by the liver may cause liver damage or even liver failure. Some examples of medications processed by the liver include acetaminophen (Tylenol), carbamazepine (Tegretol), isoniazid, and methotrexate. If you are taking any prescription medications, ask your doctor before taking vitamin A.
Neomycin (Mycifradin) -- This antibiotic may reduce the body's ability to absorb vitamin A, especially when taken in large doses.
Omeprazole (Prilosec) -- Omeprazole, used for gastroesophageal reflux disease or "heartburn," may interact with beta-carotene supplements. Researchers don' t know whether it also affects the absorption of beta-carotene from foods.
Retinoids -- These medications are a synthetic form of vitamin A and are sometimes prescribed in high doses. People who take retinoids should not take any additional vitamin A supplements. In addition, these drugs can cause severe birth defects. Women of child-bearing age must have two negative pregnancy tests and be on two forms of birth control before taking these medications. Anyone taking retinoids will be monitored closely by their doctor. Retinoids include:
Tretinoin (Retin-A) is usually prescribed as a skin cream to treat acne or reduce wrinkles and is not as concentrated as other retinoids. However, you may still want to avoid taking a vitamin A supplement while using Retin-A.
Orlistat (Alli) and Olestra -- Orlistat, a medication used for weight loss, and olestra, a substance added to certain foods, both prevent the body from absorbing fat and calories. They may also prevent the body from absorbing enough vitamin A. The Food and Drug Administration requires that vitamin A and other fat-soluble vitamins (vitamins D, E, and K) be added to food products containing olestra. In addition, people who take either prescription orlistat or over-the-counter Alli may want to take a multivitamin.
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