| Potassium is essential to all organisms and is the major
cation in cell cytoplasm with wide variety of electrochemical
and catalytic functions for enzyme systems. Potassium
constitutes five percent of the total mineral content of the
body; it is the major cation of the intracellular fluid and
there is a small amount in the extracellular fluid. With sodium,
the other "electrolyte," K participates in the maintenance of
normal water balance, osmotic equilibrium and acid-base balance.
Potassium participates with Ca in the regulation of
neuromuscular activity.
Potassium is easily absorbed, 90 % of ingested K is excreted
through the urine, and there is essentially no storage of K in
the human body requiring significant daily intake of 5,000 mg.
Muscular weakness and mental apathy are features of K
deficiency; hypokalemic cardiac failure is the most serious K
deficiency event. Diuretics, both natural and prescribed and
sweating from colds and flu or exercise, vomiting and diarrhea
increase the rate of loss of all minerals, including K, compared
with normal expected excretion.
Potassium is a mineral nutrient found primarily within cells.
Potassium is a positively charged electron (cation) and serves
an important role in skeletal muscle contraction, heart muscle
contraction, transmission of nerve impulses and the release of
energy from food.
Potassium in the blood helps maintain normal blood pressure.
A variety of population studies link high-potassium diets with a
decreased risk of essential hypertension (elevated blood
pressure), the most common form of which has no explanation.
Certain hypertensive drugs may be helped by increasing their
potassium intake, although calcium or magnesium supplementation
seems effective in other cases. Adequate potassium in the diet
may reduce the risk of stroke independent of effects on
hypertension.
Potassium appears to carry out many of the same functions
inside the cell that Na performs in the plasma and interstitial
fluid, i.e., maintenance of acid-base relationships and proper
osmotic balance. Sodium, K, and Cl are the three major
electrolytes in the body and function to maintain cation-anion
balance. Sodium is the major extracellular (outside and between
cells) cation, providing greater than 90% of the total cations
in the plasma and interstitial fluid, whereas K, the major
intracellular (within cells) cation, provides approximately 75%
of the total cations within the cell.
Active transport (energy required) mechanisms regulate some
of the concentration of specific electrolytes in the
extracellular and intracellular compartments. The intracellular-extracellular
separation of Na and K was thought to be handled by a Na pump
(Wilde, 1962). Today, however, with the development of the
Magnetic Resonance Imaging machines it is now thought that the
semi-crystalline structure of the water-cytoplasmic-matrix
within the cell actually keeps the Na outside the cell while at
the same time retains K inside the cell at the optimum ratio.
Maintenance of these concentration gradients is important for
transport of substrates into and out of the cell as well as
regulation of osmotic pressure.
Potassium contributes 50% of the osmolality of intracellular
fluid, whereas Na and Cl contribute 80% of extracellular
osmolality (Guyton, 1976). Diffusion of water maintains
equilibrium on either side of the membrane. If the concentration
of molecules outside the cell is greater than the intracellular
concentration, the cell loses water and dehydrates, while the
extracellular fluid volume increases and edema develops.
Potassium is the principle base in tissues and blood cells
and plays an important part in the regulation of acid-base
balance. Extracellular pH is rigorously maintained within a
narrow range (7.40 ± 0.05). Maintenance of this range is a
complex process involving respiration, blood buffering, and
renal excretion and reabsorption (Masero and Siegel, 1971).
Potassium is important in the transport of oxygen and carbon
dioxide through the blood and is responsible for at least half
the carbon dioxide carrying capacity of the blood.
Potassium is also important in the transmission of nerve
impulses to muscle fibers and in the contractility of the muscle
itself. An ionic balance exists between K+, Na+,
Ca 2+, and Mg2+. These ions affect
capillary and cell function and the excitability of nerve and
muscle (Thompson, 1978). For instance, K acts as a brake in
regulating heart beat and suppresses heart flutter. It also
helps prevent tetany, convulsions, and an unsteady gait.
Potassium activates or functions as a cofactor in several
enzyme systems. These include energy transfer and utilization,
protein synthesis, and carbohydrate metabolism. Some of the
enzyme systems influenced or activated by K include adenosine
triphosphatase, hexokinase, carbonic anhydrase, salivary
amylase, pyruvic kinase, and fructokinase. Potassium affecting
the uptake of amino acids into cells may form the basis for the
influence of K on growth.
Requirements
The recommended intake viewed as safe
and adequate is 11875 to 5,625 mg daily. The amounts needed are
fairly high, similar to the sodium requirement. Potassium is
excreted in urine, and excessive renal loss can be caused by
diuretics (water pills) used to treat high blood pressure.
Patients treated with diuretics generally require an extra 1,500
mg of potassium daily, and their potassium status should be
monitored regularly. Symptoms of deficiency include weakness
nausea, loss of appetite, altered mental states such as fear and
sleepiness, and impaired heart function. Mild potassium
deficiency due to diuretic therapy can be counterbalanced by
eating potassium-rich foods. Metabolic imbalances leading to the
accumulation of organic acids in the blood, such as untreated
diabetes, can cause metabolic acidosis (the accumulation of
acids in the blood) associated with the excessive excretion of
potassium. Prolonged diarrhea, vomiting and excessive use of
laxatives also promote potassium losses. Potassium deficiency
may also occur in patients with liver disease or who take
digitalis, a medication.
Large doses of potassium can lead to electrolyte imbalances
and toxic effects, especially for people with kidney disease,
diabetes or heart problems. Side effects of excessive potassium
include diarrhea, vomiting and irregular heartbeat in normal
people. Rarely, extended-release potassium tablets and capsules
can cause ulcers, bleeding and heartburn. People with kidney
failure need medical advice before eating potassium-rich foods
and potassium supplements.
Jefferson James W., "'Potassium Supplementation in Lithium
Patients: a Timely Intervention or Premature Speculation?"
Journal of Clinical Psychiatry, 53:10 (October 1992), pp.
370-72.
References:http://www.dcnutrition.com/Minerals/Detail.CFM?RecordNumber=55 |
