- A water-soluble vitamin which must be taken daily. It maintains normal carbohydrate metabolism and nervous system function and is found in high concentration in yeast and the outer layers and germ of cereals. Other major sources are beef, pork and pulses. It has no known toxicity but colours the urine a bright yellow. Lack of vitamin B1 causes beri-beri, the first deficiency disease to be recognized which led to the discovery of vitamins.