Vitamin B1 belongs is one of eight essential B vitamins. It is a water-soluble vitamin and is used in nearly every cell in the body. It is important for maintaining a healthy nervous system, converting food into energy and improving cardiovascular function. A deficiency of vitamin B1 can cause a range of symptoms, including loss of appetite, fatigue and a disorder called beriberi. By law white flour in the UK is fortified with vitamin B1.