Vitamin B-1, also called thiamine or thiamin, received its designation because it was the first B vitamin discovered.  Thiamine is essential for good health because your body uses it to form adenosine triphosphate (ATP), which supplies energy to every human cell. 

Although B-1 deficiency is not common in industrialized societies, it may occur in people undergoing kidney dialysis, those with Crohn’s disease and individuals dealing with anorexia or alcoholism. Symptoms of this deficiency include fatigue, irritability, depression and abdominal discomfort.

Some studies have suggested that thiamine may lower the risk of developing cataracts. Some people use thiamine for digestive problems, maintaining a positive attitude, increasing energy and preventing memory loss, although further research is still needed to determine whether vitamin B-1 is effective for those purposes.