Vitamin B-1 Deficiency, also known as Beriberi, is a condition caused by a lack of thiamine (vitamin B-1) in the body. Symptoms of this deficiency can include fatigue, muscle weakness, nerve damage, and heart failure. It is most commonly found in people who have diets low in thiamine, such as those who consume large amounts of processed foods or alcohol. Treatment typically involves increasing dietary intake of thiamine or taking supplements.