Vitamin A

الكاتب : نجم فلسطين   المشاهدات : 383   الردود : 0    ‏2004-05-05
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    What is "a good food source"?
    A good food source of vitamin A contains a substantial amount of vitamin A and/or carotene, which is converted to vitamin A in the body, in relation to its calorie content and contributes at least 10 percent of the U.S. Recommended Daily Allowance (RDA) for vitamin A in a selected serving size or unit of measure considered easy for the consumer to use. The U.S. RDA for vitamin A is 1,000 retinol equivalents per day. The U.S. RDA given is for adults (except pregnant or lactating women) and children over 4 years of age.
    The U.S. RDA for vitamin A is the amount of the vitamin used as a standard in nutrition labeling of foods. This allowance is based on the 1968 RDA for 24 *** and age categories set by the Food and Nutrition Board of the National Academy of Sciences. The 1989 RDA for vitamin A has been set at 800 retinol equivalents per day for women 19 to 50 years of age and 1,000 retinol equivalents for men 19 to 50 years of age.
    Where do we get vitamin A?
    In 1990, 39 percent of the vitamin A (including carotenes) in the diets of Americans came from fruits and vegetables. Dark-green vegetables and deep-yellow fruits and vegetables provided about half of the vitamin A in the form of carotenes coming from this group. Meats and dairy products each supplied about 20 percent of the vitamin A consumed. Foods that contain small amounts of vitamin A but are not considered good sources can contribute significant amounts of vitamin A to an individual's diet if these foods are eaten often or in large amounts.

    Average intake of vitamin A in the typical American diet. The "Other Foods" category includes grain products (0.5%) and miscellaneous foods (1.2%).
    Source: Gerrior SA, Zizza C. 1994 Nutrient Content of the U.S. Food Supply, 1909-1990. Home Economics Research Report No. 52. U.S. Department of Agriculture, Washington, D.C.

    Why do we need vitamin A?
    Vitamin A, a fat-soluble vitamin, is involved in the formation and maintenance of healthy skin, hair, and mucous membranes. Vitamin A helps us to see in dim light and is necessary for proper bone growth, tooth development, and reproduction.
    Do we get enough vitamin A?
    According to recent surveys of the U.S. Department of Agriculture (USDA), the average intake of vitamin A (and carotenes) by Americans 20 years of age and older met the RDA for vitamin A.

    How can we get enough vitamin A?
    Eating a variety of foods that contain vitamin A (and carotenes) is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. In fact, too much vitamin A can be toxic. The list of foods on pages 3 to 4 of this fact sheet will help you select those foods that are good sources of vitamin A as you follow the Dietary Guidelines. This list of good sources was derived from the same nutritive value of foods table used to analyze information for recent food consumption surveys of the USDA.
    How to Prepare Foods to Retain Vitamin A
    Vitamin A can be lost from foods during preparation, cooking, or storage. To retain vitamin A:
    • Serve fruits and vegetables raw whenever possible.
    • Keep vegetables (except sweet potatoes and winter squash) and fruits covered and refrigerated during storage.
    • Steam vegetables and braise, bake, or broil meats instead of frying. Some vitamin A is lost in the fat during frying.
    What about fortified foods?
    Lowfat and skim milk are often fortified with vitamin A because it is removed from milk with the fat. Margarine is fortified to make its vitamin A content the same as butter.
    Most ready-to-eat and instant prepared cereals are fortified with vitamin A. Fortified ready-to-eat cereals usually contain at least 25 percent of the U.S. RDA for vitamin A. Because cereals vary, check the label on the package for the percentage of the U.S. RDA for a specific cereal.

    What is a serving?
    The serving sizes used on the list of good sources are only estimates of the amounts of food you might eat. The amount of a nutrient in a serving depends on the weight of the serving. For example, 1/2 cup of a cooked vegetable contains more vitamin A than 1/2 cup of the same vegetable served raw, because a serving of the cooked vegetable weighs more. Therefore, the cooked vegetable may appear on the list, while the raw form does not. The raw vegetable provides the nutrient, just not enough in a 1/2-cup serving to be considered a good source.