Vitamins
Vitamins are active substances that generally have a complex chemical composition and are obtained from the external environment; they play an important role in the proper functioning of human and animal organisms. They are not synthesized by the human body and therefore must be supplied in ready or nearly ready form (provitamins) from the external environment. They are effective in relatively small quantities and can be considered as exogenous biocatalysts; their absence or deficiency leads to disturbances in metabolism or "deficiency diseases"
Source: "Explanations to the Harmonized System of Foreign Economic Activity Goods Nomenclature of the Russian Federation (HSN of Russia)" (prepared by the Federal Customs Service of Russia) (volume 1, sections I - VI, groups 1 - 29)