Thiamin (vitamin B1)
Thiamin is a co-enzyme for several central energy-yielding metabolic pathways, and therefore is required to release energy from carbohydrate. As a result thiamin requirement is related to the amount of energy consumed. Thiamin is also involved in the normal function of the nervous system and other excitable tissues, such as skeletal muscles and the heart.
Deficiency of thiamin causes the peripheral nervous system disease beri-beri. This became a public health issue in the Far East in the nineteenth century with the introduction of highly milled (polished) rice. While beriberi is now rare, it remains a problem in some parts of the world where rice is the staple food. A different condition due to thiamin deficiency, affecting the central nervous system rather than the peripheral is sometimes seen in alcoholics and people with HIV, known as Wernicke-Korsakoff syndrome. This is caused by a combination of low intake and impairment of absorption and utilisation of the vitamin.
There is no evidence of any toxic effect of high doses of thiamin as the body excretes any excess.
Whole grains, nuts, meat (especially pork), fruit and vegetables and fortified breakfast cereals are sources of thiamin in the diet. In the UK, white and brown bread flour are fortified with thiamin by law (and also with calcium, iron and niacin).