A balanced diet based on the Food Guide Pyramid should provide enough thiamin daily. A disease called beriberi, which affects the nerves and heart, is caused by thiamin deficiency. This is extremely rare in the United States, because enriched grain products are so common. 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.