LYCOS RETRIEVER 
Vitamins: Body
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Typically, a normal, well-balanced diet is sufficient in meeting all of the human body's requirements for vitamins. To help ensure that consumers know exactly how balanced their food choices are, a number of different reference guides have been developed. The most familiar in the United States is the Recommended Dietary Allowance (RDA), a guideline issued by the Food and Nutrition Board of the National Academy of Sciences. RDAs may be different depending upon age and gender. A similar, but more recently developed, guideline is the Reference Daily Intake (RDI), which provides a population-adjusted average RDA based on all ages and sex groups of RDA values. Another way of expressing vitamin recommendations is through Daily Reference Values (DRV), a loose consumer guide for labeling purposes that relates suggested amounts of certain substances that a 2000-calorie diet should contain.
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As with vitamins B6 and B12, deficiencies of folate elevate levels of homocysteine, an amino acid in the body that may increase the risk for heart disease, and possibly Alzheimer's disease. Folic acid supplements lower homocysteine levels, but with little or no impact on risk of atherosclerotic disease in the heart or in the peripheral arteries and veins. This suggests that homocysteine may be a marker of cardiovascular disease, rather than a cause. This being said, one 2007 study found that folic acid supplementation in patients with low folic acids levels substantially reduced the risk of a first stroke.
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Vitamin A is actually a family of fat-soluble vitamins. Retinol is one of the most active, or usable, forms of vitamin A, and is found in animal foods such as liver and eggs. It can be converted to retinal and retinoic acid, other active forms of the vitamin A family. Some plant foods contain orange pigments called provitamin A carotenoids that the liver can convert to retinol. Beta-carotene is a provitamin A carotenoid found in many foods. Lycopene, lutein, and zeaxanthin are ... carotenoids commonly found in food, but your body cannot convert them to vitamin A.
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A well-balanced diet contains all the necessary vitamins, and most individuals who follow such a diet can correct any previous vitamin deficiencies. However, persons who are on special diets, who are suffering from intestinal disorders that prevent normal absorption of nutrients, or who are pregnant or lactating may need particular vitamin supplements to bolster their metabolism. Beyond such real needs, vitamin supplements are ... often popularly believed to offer “cures” for many diseases, from colds to cancer; but in fact the body quickly eliminates most of these preparations without absorbing them. In addition, the fat-soluble vitamins can block the effect of other vitamins and even cause severe poisoning when taken in excess.
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The discovery of vitamins began early in the 20th century. It is likely that some still are undiscovered. Although vitamins are needed in only small amounts, they are essential for good health. They help keep the body's tissues healthy and its many systems working properly. Each vitamin has specific roles to play.
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Many vitamins can not be made by the body itself. The body needs to obtain them through other routes, usually through food. A short term lack of a certain vitamin is usually not a problem, as the body is able to store vitamins for a short time. Not having a certain vitamin for a longer period of time can lead to different diseases, depending on the lacking vitamin. Probably the best-known of these diseases is scurvy, which results from not having enough Vitamin C.
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