What Is Vitamin A?
This famed vision-enhancing nutrient was isolated in 1930, the first fat-soluble vitamin to be discovered. The body acquires some of its vitamin A through animal fats. The rest it synthesizes in the intestines from the beta-carotene and other carotenoids abundant in many fruits and vegetables.
Vitamin A is stored in the liver. Small amounts are also found in most human tissues in chemical forms called retinoids, a name related to the vitamin's critical effect on vision (and particularly on the retina of the eye).
Although vitamin A is probably best known for promoting and maintaining healthy eyesight, it has other important functions as well. One of its major contributions is to improve the body's resistance to infection. It does this in part by maintaining the health of the skin, mucous membranes, and other surface linings (intestinal tract, urinary tract, respiratory tract) so that harmful bacteria and viruses can't get into your body.
Another way that vitamin A boosts immunity is by enhancing the infection-fighting actions of the white blood cells called lymphocytes. Vitamin A is also vital to the growth of bones, the division of cells in your body, and to human reproduction.
Specifically, vitamin A may help to:
Promote healthy vision. This nutrient is involved in the proper functioning of the retina of the eye and is essential for the integrity of the mucous membranes surrounding the eyes. Itis invaluable in preventing night blindness, and assisting the eye in adapting from bright light to darkness. Vitamin A eyedrops (available over-the-counter) are also effective in treating a disorder known as dry eye, caused by a failure of the tear glands to produce sufficient fluid.
Ward off infections such as colds, flu, and bronchitis. By supporting the healthy maintenance of mucous membranes, vitamin A may be useful for fighting colds and other common infections. In the case of chronic bronchitis, the nutrient encourages healing of damaged lung tissue and may even help to prevent recurrences. In a Brazilian study of men with chronic lung disease, it was found that participants who were given 5,000 IU of vitamin A daily for 30 days could breathe more easily than those who took a placebo.
Fight cancer. This immune-system booster may be of value in combating breast and lung cancers and in increasing the survival rate of leukemia patients. It may also protect against the development of a melanoma (a form of skin cancer that is often malignant). In addition, some research indicates that cancer patients with high vitamin A levels respond particularly well to chemotherapy treatment.
Treat skin disorders, such as acne, eczema, psoriasis, and rosacea. Research has shown that vitamin A is vital for healthy skin. In the l940s, high doses were prescribed for conditions such as psoriasis and acne. This practice ended abruptly with the realization that such high doses are toxic.
Today, doctors commonly prescribe safer medications made from derivatives of vitamin A, such as retinoic acid (Retin A, a popular prescription cream for acne and wrinkles) and isotretinoin (Accutane, an oral drug prescribed for severe acne). Short of prescription medications, however, careful use of moderate oral doses--see the Dosage Recommendations Chart--may be key to promoting skin health.
Control cold sores. Vitamin A has well-known antiviral properties, and it may be worth trying orally to boost immunity. Liquid forms can even be applied directly to cold sores, also known as fever blisters, which develop as a result of a herpes simplex viral infection.
Correct hair and scalp problems. One of the signs of a vitamin A deficiency (albeit a severe one) is flakiness of the scalp. Correcting the deficiency may eliminate this often itchy and embarrassing condition. But keep in mind that more isn't always better when it comes to vitamins: Too much vitamin A (more than 100,000 IU a day) taken over a long time can actually cause hair loss (among other problems).
Encourage healing of minor burns, cuts, and scrapes. When applied to the skin, vitamin A cream or ointment can accelerate the healing of minor cuts, burns, and scrapes.
Protect against certain gastrointestinal problems. Because it is helpful in protecting the lining of the digestive tract, vitamin A may ease symptoms of inflammatory bowel disease and ulcers. A large study of doctors ages 40 to 75 showed that those who were least likely to suffer from ulcers of the duodenum (a part of the small intestine) were the ones who had the highest intake of vitamin A, mainly from a combination of diet, multivitamins, and supplements.
Note: Vitamin A has also been found to be useful for a number of other disorders. For information on these additional ailments, see our Dosage Recommendations Chart for Vitamin A.
The RDA for vitamin A is 5,000 IU daily for men, and 4,000 IU daily for women.
If You Get Too Little?
Few people in the United States suffer from a deficiency of vitamin A, although those with vitamin-poor diets are at risk (indeed, some elderly individuals fall into this category). Low levels can significantly reduce resistance to infection, cause a flaky scalp, and contribute to heavy or prolonged menstrual periods. And very low levels of this nutrient can cause night blindness or even complete blindness.
If You Get Too Much?
Excessive vitamin A can cause serious health problems. It's virtually impossible to get too much of this nutrient from foods; the body makes only what it needs from carotenoid-rich fruits and vegetables. But care is needed when taking supplements containing "preformed" vitamin A, meaning it has been synthesized for you already during the manufacturing process.
Symptoms of vitamin A toxicity include dry and cracking skin, brittle nails, excessive hair loss, bleeding gums, weight loss, irritability, nausea, and fatigue. An extremely high single dose--500,000 IU, for example--can cause vomiting and weakness.
General Dosage Information?
--Some sources measure vitamin A in retinol equivalents (RE) rather than international units (IU); one RE is equivalent to 3.3 IU.
--Most multivitamins offer vitamin A as beta-carotene, an antioxidant that the body can convert to vitamin A. However, the amount of vitamin A produced during this conversion is small and inadequate for those conditions in which vitamin A itself was shown to be therapeutic.
For improved resistance to colds, flu, and other viral infections: Take 50,000 IU twice a day for five days; then reduce to 25,000 IU a day, if necessary, for no more than 10 days.
Be sure to check out our Dosage Recommendations Chart for Vitamin A, which lists therapeutic dosages for specific ailments at a glance.
Guidelines for Use?
Make sure to take vitamin A supplements with food; some fat in the diet will enhance absorption.
Both vitamin E and zinc aid the body in using vitamin A. In turn, vitamin A facilitates the absorption of iron from foods. A good daily multiple vitamin/mineral will provide the necessary amounts.
Don't take vitamin A with isotretinoin or other acne drugs. Together, they may cause high blood levels of vitamin A, which can lead to unwanted side effects.
Note: For information on interactions with specific generic drugs, see our WholeHealthMD Drug/Nutrient Interactions Chart.
Don't exceed recommended doses of vitamin A. Large doses of preformed vitamin A can build up to toxic levels.
If you're pregnant or trying to get pregnant, don't take more than 5,000 IU of vitamin A daily. Higher amounts may result in birth defects. Practice birth control if consuming doses greater than 5,000 IU, and for a month after stopping.