Thiamin was the first B-vitamin discovered, and was therefore called vitamin B-1. It is needed for energy metabolism, in particular the release of energy from carbohydrates. Thiamin is essential for the normal functioning of the nervous system. It helps to regulate appetite and supports normal muscle function, including the heart muscle.

The importance of thiamin in the normal functioning of the nervous system is in part due to its role in the synthesis of acetylcholine, a neurotransmitter which can affect many functions including mood and memory.

A thiamin deficiency results in the disease beriberi. Thiamin deficiency is rare in the U.S., except with chronic alcoholism. Alcohol impairs the absorption and storage of thiamin. Thiamin deficiency is associated with some of the symptoms of alcoholism such as mental confusion, visual disturbances and staggering gait.

Beriberi can affect the cardiovascular system and the nervous system. Additional deficiency symptoms include fatigue, anorexia, insomnia, muscle aches and pains, depression, heart and digestive system problems.