K – Potassium is found in igneous rocks at 20,000 ppm; shale at 26,000 ppm; sandstone at 10,700 ppm; limestone at 2,700 ppm; fresh water at 2.3 ppm; sea water at 380 ppm; soil at 14,000 ppm (a major exchangeable cation in all, but the most alkaline soils); marine plants at 52,000; land plants at 14,000 ppm; marine animals at 5,000 to 30,000 ppm; land animals at 7,400 Ppm (highest levels in soft tissues).
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.
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.
Acute toxicity from orally administered K in healthy humans is unusual. Large doses of K salts are considered moderately toxic although they usually induce vomiting, and most of the absorbed K is rapidly excreted by the normal kidney (Gleason et al., 1969). In individuals with kidney, heart, or liver disease, however, the possibility for elevated blood K exists.
Hyperkalemia (high blood levels of K) may occur in humans (Ettinger, 1978)
1. in acute or chronic renal insufficiency;
2. after extensive tissue trauma, which results in liberation of intracellular K+ ions;
3. during administration of large amounts of K;
4. in metabolic acidosis, in which hydrogen ion replaces the K ion in cells, thus raising plasma K+;
5. when normally well-tolerated amounts of K salts are administered concomitant with certain diuretics;
6. after surgery, usually associated with oliguria, extravascular accumulations of blood, multiple transfusions, and acidosis; and
7. in acute adrenal insufficiency.