Vitamins are defined as essential constituents of the diet that are not synthetized by humans. Some vitamins are synthesized to some extent, but in amounts that are usually inadequate to support health. Most vitamins were discovered during the investigation of severe deficiencies such as scurvy (vitamin C), rickets (vitamin D), megaloblastic anemias (vitamin K and folate), pellagra (niacin) and beriberi (thiamine). Most vitamins are not one specific molecule, but a group of related compounds that are capable of providing the necessarily essential molecular ingredient (thus nicotinic acid and nicotinamide for niacin and phytonadione and menadione for vitamin K). The recommended daily amounts or recommended daily intakes of most vitamins have been established by the Food and Nutrition Board of the Institute of Medicine. These recommendations provide guidance for standard dosing of vitamins in dietary supplements and multivitamin preparations. Approximately one-third of adult Americans take multivitamins and a substantial number take specific vitamin supplements.
When taken within the range of recommended amounts, vitamins have not been implicated in cases of drug induced liver injury. Even in high doses, most vitamins have few adverse events and do not harm the liver. Many vitamins are normally concentrated in, metabolized by and actually stored in the liver, particularly the fat soluble vitamins. The two exceptions to the lack of harm to the liver by higher doses of vitamins are vitamin A and niacin, both of which can cause distinctive forms of liver injury when taken in high doses.
References updated: 09 May 2016