Vitamin B1 deficiency, also known as thiamine deficiency, occurs when the body does not get enough of this essential nutrient. Thiamine is crucial for converting carbohydrates into energy and plays a vital role in nerve function. A lack of thiamine can lead to symptoms such as fatigue, irritability, and muscle weakness. In severe cases, it can cause beriberi, a condition that affects the cardiovascular and nervous systems. People at higher risk for thiamine deficiency include those with poor diets, chronic alcohol consumption, or certain medical conditions. Treatment typically involves dietary changes and thiamine supplements. Eating foods rich in thiamine, like whole grains, legumes, and nuts, can help prevent this deficiency.