Role: Major intracellular cation. Involved in transmitting nerve impulses, regulating blood pressure, and controlling muscle contractility.
Deficiency: Muscle cramps, heartbeat irregularities, loss of appetite, weakness, drowsiness.
Sources: Bananas, potatoes, avocados, oranges, other fruits and vegetables; meats, fish, seafood, poultry; milk and dairy products.
Toxicity: Excess unlikely in healthy people. No more than 18,000 mg is advised. Acute hyperkalemia from excess intake can cause cardiac arrest.