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 deficiency is rare, but can occur in people who get most of their calories from sugar or alcohol. People with thiamine deficiency have difficulty digesting carbohydrates. As a result, a substance called pyruvic acid builds up in their bloodstream, causing a loss of mental alertness, difficulty breathing, and heart damage (a disease known as beriberi).
Some preliminary evidence suggests that thiamine — along with other nutrients — may lower risk of getting cataracts.