Before grains were enriched, it was much more common. Severe thiamin deficiency is rare in the United States today. Mild deficiencies are more common. Exceptions may be found with chronic alcoholism , fasting, the elderly, and chronic dieting. Deficiency is rare mainly due to enriched grain products.
Symptoms usually show up in the nerves, stomach, and heart.
If deficiency continues, symptoms can get worse, and some damage can be permanent. There is little chance of thiamin toxicity, even when it is taken at high doses. Because it is water soluble and not stored in the body, it is not likely to build up to toxic levels. In elderly people with decreased concentrations of thiamin, supplementation has enhanced quality of life by decreasing both blood pressure and weight. In isolated cases, however, thiamin toxicity has occurred from injections or concentrated formulas used with hospital patients.