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Vital Vitamins
There are 13 known vitaminsorganic compounds that are required to keep the body healthy and free of disease. Some, such as A, D, and E, are fat-soluble and can damage the liver if consumed in excess amounts; others, such as C, are water-soluble, and excess amounts of them will be flushed out of the body. The following list tells you what each vitamin does for your body, how much of each you should consume, and the best food sources for each. You'll learn more about the top nutrient-packed foods in later chapters.
Vitamin A
What it does: promotes growth of cells and tissue repair, maintains healthy skin; aids in night and color vision; and boosts the immune system. Its precursor, beta-carotene, is an antioxidant.
What it may do: prevent premature aging of the skin; as Retin-A, it is commonly used to treat wrinkles. It may also prevent cataracts among the elderly; a recent study found that women who ate foods rich in beta-carotene had a 39 percent lower risk of developing cataracts. Several studies show a link between beta-carotene intake and reduced risk of heart disease and stroke. And beta-carotene and vitamin A may provide strong protection against many forms of cancer, including cancers of the stomach, colon, mouth, throat, esophagus, bladder, cervix, lungs, and breasts.
RDA: 5,000 IUs (international units). Warning: because vitamin A can be toxic in high doses, you should not consume more than 25,000 IUs per day unless under supervised care.

 
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