Not until the beginning of the twentieth century was it recognized that certain substances were essential in the diet to prevent or cure some disease. These substances are now known as vitamins. They are vital for growth, good health, and maintenance of the normal functions of the body. A well-balanced diet should provide all the vitamins we normally require. Those of us who are fortunate enough to be able to buy sufficient food should not suffer from vitamin deficiency. However, for various reasons, some people do not maintain a balanced diet. People often lose their appetite because of illness. People living alone may not bother to eat proper meals, and people on a diet may not eat sufficient quantities of necessary foods.