Potassium is an element (and an electrolyte) that's essential for the body's growth and maintenance. It's necessary to keep a normal water balance between the cells and body fluids. Potassium also plays an essential role in the response of nerves to stimulation and in the contraction of muscles. Cellular enzymes need potassium to work properly.
A potassium deficiency due to increased urinary loss often occurs when medication for certain heart diseases is used to prevent sodium and water retention. To overcome this loss, physicians often suggest eating more foods high in potassium.