Vitamin A is a fat-soluble vitamin needed for the growth of cells and bone, reproduction, healthy eyes and skin, and the maintenance of healthy respiratory, intestinal, and urinary tracts. This vitamin occurs in foods such as dark green and yellow vegetables, milk, eggs, cheese, squash, carrots, and in fruits such as apricots and cantaloupe. Vitamin A is used as a supplement for treatment of vitamin A deficiency, and it can also be used for other purposes.
A Answers (4)
Stacy Wiegman, PharmD, Pharmacy, answered
Marjorie Nolan Cohn, Nutrition & Dietetics, answered on behalf of Academy of Nutrition and Dietetics
Vitamin A is a fat-soluble vitamin. It also called retinol, mainly because it produces pigments in the eye's retina. The eye needs a specific metabolite of vitamin a, called retinal which is important for vision. Vitamin A is also important for healthy teeth, skeletal tissue, soft tissue, the skin, and mucous membranes.
Vitamin A comes from two main types of foods:
Retinol - It is the form of vitamin A absorbed when eating animal foods, such as cod liver oil, butter, liver, eggs, cheese and milk.
Carotenes - such as alpha-carotene, beta-carotene, gamma-carotene, and xanthophyll beta- cryptoxanthin. Carotene is an orange photosynthetic pigment crucial for plant photosynthesis. The orange colors of carrots, sweet potatoes and cantaloupe melons come from its carotene content. Lower carotene concentrations are what give the yellowish coloration to butter and milk-fat. Some omnivores have yellow-colored body fat, such as chickens and humans.
Vitamin A is a fat-soluble vitamin that is derived from two sources: preformed retinoids and provitamin carotenoids. Retinoids, such as retinal and retinoic acid, are found in animal sources, such as liver, kidney, eggs, and dairy produce. Carotenoids, such as beta-carotene (which has the highest vitamin A activity), are found in plants such as dark or yellow vegetables and carrots.
Natural retinoids are present in all living organisms, either as preformed vitamin A or as carotenoids, and are required for biological processes such as vision and cellular growth. A major biologic function of vitamin A (as the metabolite retinal) is in the visual cycle. Research also suggests that vitamin A may reduce the mortality rate from measles, prevent some types of cancer, aid in growth and development, and improve immune function.
Recommended dietary allowance (RDA) levels for vitamin A oral intake have been established by the U.S. Institute for Medicine of the National Academy of Sciences to prevent deficiencies in vitamin A. At recommended doses, vitamin A is generally considered nontoxic. Excess dosing may lead to acute or chronic toxicity.
Vitamin A deficiency is rare in industrialized nations but remains a concern in developing countries, particularly in areas where malnutrition is common. Prolonged deficiency can lead to xerophthalmia (dry eye) and ultimately to night blindness or total blindness, as well as to skin disorders, infections (such as measles), diarrhea, and respiratory disorders.
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Vitamin A is actually a family of substances called retinoids that includes retinol, retinal, and retinoic acid. These are called preformed vitamin A because they are in a form that your body readily uses. Retinol is the most usable of the three forms and can be converted to both retinal and retinoic acid in your body.
Preformed vitamin A is found only in foods from animal sources, such as liver and eggs, and is added to all processed milk. Plant food sources do not contain preformed vitamin A, but some do contain provitamin A carotenoid, which can be converted to retinol in your body. Carotenoids are the yellow-red pigments that give carrots, butternut squash, and cantaloupe their vibrant, deep orange color.