Vitamin B1, also called thiamine or thiamin, is one of 8 B vitamins. Like other B complex vitamins, thiamine is considered an "anti-stress" vitamin because it may strengthen the immune system and improve the body's ability to withstand stressful conditions. It is named B1 because it was the first B vitamin discovered.
Thiamine is found in both plants and animals and plays a crucial role in certain metabolic reactions. For example, it is required for the body to form adenosine triphosphate (ATP), which every cell of the body uses for energy.