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Vitamins are chemicals that are vital for life, to the extent that absence of these chemicals will result in serious illness of one type or other. In the industrialized West vitamin-deficiency diseases are not very common, and usually (though not always) related to chronic alcohol or other substance abuse; most of the remaining cases are related to genetic and/or physiological disorders. You only need a certain amount of each vitamin (eating carrots will only improve your eyesight if you have a Vitamin A deficiency), and too much of some vitamins (called hypervitaminosis) can be toxic and even lethal.[note 1] Despite this, an enormous number of Americans take vitamin supplements daily, fuelling a multi-million dollar industry. The term vitamin was coined in 1911 by Casimir Funk.
|Vitamin name||Chemical Name|
|Vitamin A||Retinoids (retinol, retinoid) and carotenoids|
|Vitamin B5||Pantothenic acid|
|Vitamin B9||Folic acid|
|Vitamin C||Ascorbic acid|
|Vitamin D||Ergocalciferol and Cholecalciferol|
|Vitamin E||Tocopherol and Tocotrienol|
This is a relatively short list, and most of these items can be found in a normal diet without much effort, the most notable exceptions being vegetarians and vegans, as vitamin D and vitamin B12 occur primarily in animal products (which doesn't mean either type of diet is necessarily unhealthy, just that they require more care to get everything one needs).
Clearly there are situations when vitamin supplements can be useful, and there is a thriving industry supplying such pills. However, many companies want to go further in marketing supplements, and arguing that there are other chemicals that are "vitamin like" or desirable for health. See pseudovitamin for some examples. In 1998, choline was found to be necessary for human nutrition and to probably meet the definition of a vitamin, making it the only true recent addition to the vitamin category; its actual status is still unsettled.
There are other substances besides vitamins also necessary for human nutrition. Essential chemical elements are classified as minerals, not as vitamins. Water, fats (and essential fatty acids), and proteins are also necessary, but are not vitamins because they are needed in large amounts. In general, a vitamin is an organic compound (not a single element) needed by the human body in small amounts that is not always synthesized by the body in sufficient amounts and must be obtained through the diet. Vitamins D and K, although synthesized in the body, remain classified as vitamins because outside sources of these are sometimes needed.
- The reasoning goes something like: "Vitamin C is essential for health, so lots of vitamin C should be even better!" The fallaciousness of this can be demonstrated with the statement: "Vitamin A is essential for health, so lots of vitamin A is even better!" (Vitamin A causes liver damage in high doses.) Or, to frame it in terms of something commonly known by CAM believers, "Sodium is essential for health, so lots of sodium is even better!"