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Vitamin A


Alternative names

Vitamin A deficiency; Deficiency - Vitamin A

Definition

Vitamin A is a fat-soluble vitamin.

Function

Vitamin A helps form and maintain healthy teeth, skeletal and soft tissue, mucous membranes, and skin. It is also known as retinol because it generates the pigments in the retina .

Vitamin A promotes good vision, especially in dim light. It may also be required for reproduction and breast-feeding.

Beta-carotene , which has antioxidant properties, is a precursor to Vitamin A. Antioxidants quench free radicals, which are unstable substances that can react with and damage cells, tissues and organs. Free radicals are believed to be associated with many of the degenerative changes seen with aging. However, it is not yet known whether antioxidants can prevent these changes and studies have been conflicting. For example, one study found increased cancer risk in smokers who took high doses of beta carotene.

With Vitamin A, as with many other vitamins, a certain amount is necessary, but too much is toxic.

Food Sources

Vitamin A comes from animal sources, such as eggs, meat, milk, cheese, cream, liver, kidney, cod and halibut fish oil. However, all of these sources -- except for skim milk that has been fortified with Vitamin A -- are high in saturated fat and cholesterol .

The precursor form, beta-carotene, is found in plants. Sources of beta-carotene are carrots, pumpkin, sweet potatoes, winter squashes, cantaloupe, pink grapefruit, apricots, broccoli, spinach, and most dark green, leafy vegetables. The more intense the color of a fruit or vegetable, the higher the beta-carotene content. These vegetable sources of beta-carotene are free of fat and cholesterol.

The body regulates the conversion of beta-carotene to Vitamin A based on its needs.

Side Effects

If you don't get enough Vitamin A, you are more susceptible to infectious diseases and vision problems. However, large doses of Vitamin A can be toxic. Large doses can also cause abnormal fetal development in pregnant women.

Increased amounts of beta-carotene can turn the color of skin to yellow or orange. The skin color returns to normal once the increased intake of beta-carotene is reduced.

Recommendations

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid .

Update Date: 1/18/2003

Steven Angelo, M.D., Assistant Professor of Medicine, Yale School of Medicine, New Haven, CT. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT
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