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Vitamins are organic nutrients which the body requires in very small quantities for normal growth and metabolism. Vitamins are not themselves energy sources (such as carbohydrates or fats) although some are essential for the body to be able to convert energy sources into energy. Most vitamins are not manufactured within the body but must be obtained from food or other sources (e.g., the body converts sunlight into vitamin D). However, generous amounts of vitamins are present in many food sources. Most doctors feel that a healthy diet should provide all of the vitamins needed by the body, and that additional sources, such as dietary supplements or multivitamins, are unnecessary. Other doctors sometimes suggest that a patient take a supplement to increase intake of a particular vitamin to remedy a specific deficiency.

Some vitamins (e.g. vitamins A, D, E, K) are "fat-soluble", meaning that the body stores them in fat. Excessive or prolonged intake of these vitamins, at levels that exceed the recommended daily allowance (RDA), can have toxic effects.

Other vitamins (e.g. vitamins B and C) are "water-soluble", meaning that they do not tend to accumulate in the body; unused quantities are instead excreted in urine. Consequently, excessive dietary intake does not tend to prove toxic, and deficiency of water-soluble vitamins is more common.

Further Reading:

The Mayo Health Clinic (http://www.mayohealth.org) maintains a current list of information about dietary suppelements.

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