This is present in many foods especially milk, egg yolk and liver. As with many other vitamins of the B group it is added to bread and many breakfast cereals. It is not affected by cooking but is destroyed by a combination of heat and ultraviolet light. For this reason milk left on the doorstep for several hours on a hot summer's day will retain little of this vitamin. Riboflavin is important in the chemical processes by which energy is obtained from food.
Deficiencies are rare and usually occur in association with lack of thiamine and nicotinic acid.
If the vitamin is deficient the lips and tongue become sore because of inflammation and the eyes become red and painful. Its functions are similar to those of riboflavin. Deficiencies are rare except among those people for whom maize forms the staple diet. Symptoms are loss of weight and appetite and general ill health. This is present in many foods, especially whole-grain cereals, meat, liver and vegetables.