A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Vitamin B1 helps some enzymes work properly, helps break down sugars in the diet, and keeps nerves and the heart healthy. It is found in pork, organ meats, peas, beans, nuts, and whole grains. Vitamin B1 is water-soluble (can dissolve in water) and must be taken in daily. Not enough vitamin B1 can cause a disease called beriberi (a condition marked by heart, nerve, and digestive disorders). Too much vitamin B1 may help cancer cells grow faster. Also called thiamine.