The complex of clinical disturbances long known as beriberi has been recognized since early in the twentieth century as arising because of a deficiency of thiamine. Like others in the group of B vitamins, thiamine has essential coenzyme functions in intermediary metabolism. The principal role of this water-soluble molecule is that of precursor of thiamine pyrophosphate (thiamine diphosphate), a coenzyme (often referred to as cocarboxylase) in energy generation through oxidative decarboxylation of alpha-ketoacids, such as pyruvic acid and alpha-ketoglutaric acid. Thiamine pyrophosphate serves also as the coenzyme for transketolase, a catalyst in the pentose phosphate pathway of glucose metabolism. Measurement of transketolase activity in erythrocytes and stimulation of activity by added thiamine pyrophosphate is the most convenient and sensitive method for detecting human thiamine deficiency. As the pyrophosphate and/or the triphosphate, thiamine appears also to have a role in facilitating conduction in peripheral nerves.

Like most vitamins, thiamine cannot be synthesized in the body and must be acquired in the diet. It is found in many foods and is most abundant in grains, legumes, nuts, and yeast. All meats and most dairy products contain some thiamine, but the richest sources are pork and eggs. Milk, however, is not a rich source. As a water-soluble vitamin, thiamine is easily lost in cooking water. Fish can supply good amounts, but with fermentation of raw fish, the enzyme thiaminase may alter the thiamine molecule, blocking its biological activity. Dietary thiamine is actively absorbed, mainly in the small intestine. The recommended daily dietary allowance is 1.2 to 1.5 milligrams for adult males and 1.0 to 1.1 milligrams for adult females, depending upon age, with a 50 percent increase in requirements during pregnancy and lactation. Up to about 25 milligrams can be stored by a healthy person, especially in heart muscle, brain, liver,kidney, and skeletal muscle.