POTASSIUM

Potassium (K) in the form of K+ is the most essential cation (a positively charged ion) of the cells. Its high intracellular concentration is regulated by the cell membrane through the sodium-potassium pump. Most of the total body potassium is found in muscle tissue. Total body potassium has been used as a measure of lean body mass, of muscle mass, or (more accurately) of cell mass. Because of its association with the metabolizing, oxygen-consuming portion of the body, a decline in total body potassium is usually interpreted as a loss of muscle mass due to a catabolic condition. Potassium exists in nature in three isotopes: ³⁹K (93.26%), ⁴⁰K (0.0117%) and ⁴¹K (6.73%). ⁴⁰K is radioactive and responsible for most of the naturally occurring internal radioactivity in the body. This property enables investigators to monitor total body potassium values as a function of age and disease.

IMPORTANCE: Works with sodium to regulate the body's waste balance and normalize heart rhythms; aids in clear thinking by sending oxygen to the brain; preserves proper alkalinity of body fluids; stimulates the kidneys to eliminate poisonous body wastes; assists in reducing high blood pressure; promotes healthy skin. 

Deficiencies: With the exception of starvation, low or declining total body potassium is not a result of insufficient dietary intake but the outcome of a catabolic, protein wasting condition which reduces the total cell mass of the body. Hypokalemia (low serum K) is the result of excessive loss of K in the urine, usually as a result of use of diuretic agents to treat hypertension. Hypokalemia may result in cardiac failure. May result in poor reflexes, nervous disorders, respiratory failure, cardiac arrest, muscle damage.

Dietary recommendations: The Estimated Minimum Requirement for potassium for adolescents and adults is 2000 mg or 50 mEq/day. The usual dietary intake for adults is about 100 mEq/day. For hypertension patients using diuretic medications, it is recommended often to supplement their diet with orange juice, bananas and vegetables which contain high amounts of potassium. Increased potassium intake helps maintain normal plasma levels. However, the blood level of potassium (which is sensitive to diet) is not indicative of total body potassium which is an index of cell mass and muscle.

Food sources: Most foods contain potassium. The best food sources are fruits, vegetables and juices; potassium also is present in meats and cereals. 

Toxicity: The fraction of potassium which is present outside the cells plays an active role in the propagation of electrical signals between neurons, skeletal muscle function and regulation of blood pressure. Urinary excretion protects against the accumulation of high levels of potassium. However, acute hyperkalemia can be lethal by causing cardiac arrest.

Recent research: Most of the recent research is related to the importance of total body potassium as an index of cell mass. The accelerated loss of total body potassium compared to protein loss in AIDS patients can be used to predict the time of death of the patient. Total body potassium is depleted with age, a phenomenon associated with sarcopenia (loss of skeletal muscle mass and function with age).