Thiamine deficiency is not common. However, people with Crohn's disease or anorexia, those undergoing kidney dialysis and people with alcoholism are at risk of having low thiamine levels.
A severe deficiency, which is rare in the United States, makes digesting carbohydrates difficult and causes a buildup of pyruvic acid in your blood. That situation can lead to problems with the nervous system, like confusion, loss of feeling in hands and feet and even paralysis of the lower legs. It can also cause breathing difficulties and heart damage.