Thiamin is a member of the B complex vitamins, and an essential component of human nutrition. It is used by all living organisms, but can be produced only in plants, fungi and bacteria. The most concentrated sources of dietary thiamine are pork, yeast and yeast extract, whole grains, legumes, nuts and seeds, but it is also a valuable dietary supplement.
Refinement and processing of grains once contributed to widespread deficiency, and most processed grain products are now required to supplement their thiamine content. Other foods with a naturally rich source of thiamine include brown rice, sunflower seeds, oatmeal, eggs, liver, kale, potatoes, cauliflower, asparagus and oranges.
Thiamin deficiency has significant neurological effects, which can be fatal if left untreated. These include loss of vision, an amnesiac and attention deficiency syndrome called Korsakoff's syndrome, and in particular beriberi, a disease affecting the cardiovascular and/or the peripheral nervous system.
Symptoms of the disease include impaired sensory perception, weakness and pain in limbs, emotional disturbance, swollen body tissues and weight loss. In its advanced state, beriberi causes cardiac failure and death. Thiamin is listed by the WHO as one of the most important elements in a basic health system.