Vitamer
A vitamer (/ˈvaɪtəmər/) is any of the related forms in which some vitamin occurs. Each vitamer of a particular vitamin is a compound that performs the functions of that vitamin and prevents the symptoms of deficiency of the vitamin.
Early research identified vitamins by their ability to cure vitamin-specific deficiency diseases. For example, vitamin B1 was first identified as a substance that prevented and treated beriberi. Subsequent nutrition research has revealed that all vitamers exhibit biological activity against their specific vitamin deficiency, although different vitamers exhibit different potencies against those diseases.
A set of vitamers with related biological activity are grouped together by a general name, or generic descriptor, that refers to similar compounds with the same vitamin function. For example, vitamin A is the generic descriptor for the class of vitamin A vitamers which include retinol, retinal, retinoic acid, and provitamin carotenoids such as beta-carotene among others.