Vitamins participate in the growth process and are essential for the human health. There are also presented compounds that are now no longer considered as vitamins.
The word vitamin is derived from the Latin word "vita" which means "life" and word "amine",
therefore "amine that necessary for life", although the discovery of other vitamins shown that all vitamins does not contain an amino group. The first experimental tests of biochemistry and physiology of vitamin belong to the Russian researcher Lunin, and the name "vitamin" was first introduced by Casimir Funk in 1911 for the substance isolated from rice husks... → About vitamins (in general).
Given that at the time when the individual vitamins discovered and their structure was unknown they were denoted by letters (A, B, C, D, etc.). These names were preserved to this day, because the structure of vitamins may vary significantly and they can not be
classified into one common group of chemical compounds.