Potassium is a mineral that plays many critical roles in the body. Food sources of potassium include fruits (especially dried fruits), cereals, beans, milk, and vegetables. Potassium is used for treating and preventing low potassium levels.It is also used to treat high blood pressure and prevent stroke.otassium is a mineral that plays many critical roles in the body. Food sources of potassium include fruits (especially dried fruits), cereals, beans, milk, and vegetables. Potassium is used for treating and preventing low potassium levels.