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
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
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).