A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. ^[1] A compound is called a vitamin when it cannot be synthesizedin sufficient quantities by an organism, and must be obtained from thediet. Thus, the term is conditional both on the circumstances and theparticular organism. For example, ascorbic acid functions as vitamin C for some animals but not others, and vitamins D and K are required in the human diet only in certain circumstances. ^[2] The term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but are otherwise required less often.

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