Thiamin (also spelled thiamine) is a water-soluble vitamin required by every tissue in the body. First isolated in 1926, thiamin was the first B-vitamin to be discovered, which is why it is also known as vitamin B-1. It is involved in numerous enzymatic processes relating to energy production, carbohydrate metabolism, and nerve cell function. Most of the thiamin in the body is bonded to phosphate molecules (phosphorylated) to form energy-storing compounds such as thiamin monophosphate, thiamin diphosphate, and thiamin triphosphate. The energy potential of these compounds depends on the number of phosphate molecules they contain; thiamin triphosphate has high energy potential, while thiamin diphosphate has less, and thiamin monophosphate has the least. Each of these forms serves different functions in the body. Unphosphylated (a.k.a. "free") thiamin does not appear to be biologically active. Supplemental thiamin (as found in multi-vitamin and B-complex formulas) is usually in the form of thiamin salts such as thiamin hydrochloride or thiamine mononitrate.
Thiamin is found in a wide variety of foods. Among the best sources are organ meats (especially liver), brewer's yeast, whole grains, nuts, peanuts, and sunflower seeds. Other sources of thiamin include meat, egg yolks, poultry, fish, plums, prunes, raisins, broccoli, Brussels sprouts, and fortified flour. Foods may lose much of their thiamin content through cooking or exposure to ultraviolet light, nitrites, sulfites, or live yeast. Thiamin is also destroyed by alcohol, enzymes found in raw seafood, and tannins found in coffee and tea.
The phosphorylated forms of thiamin serve as cofactors in numerous enzymatic processes in the body, most notably those involved in energy metabolism and in brain and nerve cell function. Because thiamin is essential for the conversion of carbohydrates into energy, high carbohydrate intake increases the body's thiamin requirements.
The reference daily intake (RDI) for thiamin is 1.5 mg per day. Because thiamin is found in a wide variety of foods, most people receive this amount through dietary intake. As a water-soluble vitamin, thiamin is not stored in the body, and must be consumed daily. Thiamin has no known toxicity, even at very high doses. Excess thiamin is excreted in the urine.