Potassium, sodium, and chloride make up the principal electrolytes within the body. In contrast to sodium and chloride, nutritional concerns with potassium are mainly concerned with the possibility of underconsumption.
Potassium is the major intracellular electrolyte and exists as the fully water-soluble cation. More than 90% of dietary potassium is absorbed from the diges-tive tract.
Few dietary components affect absorption of potas-sium, although olive oil can increase and dietary fiber decrease absorption to some extent. The “average” 70 kg man contains about 120 g of potassium, depend-ing on muscle mass, with men having proportionally greater muscle mass, and hence potassium, than women. Almost all of the body potassium is exchange-able, intracellular concentration being more than 30 times the concentration of the ECF. Potassium is distributed within the body in response to energy-dependent sodium redistribution. Various hormonal and other factors regulate potassium homeostasis, both within cells and with the external environment. Hyperkalemia (too much potassium in the ECF) stimulates insulin, aldosterone, and epinephrine (adrenaline) secretions, which promote the uptake of potassium by body cells. The aldosterone hormone also stimulates potassium excretion by the kidney and, at the same time, conserves sodium. Hypokale-mia has opposite effects, such that more potassium is released from cells. As with sodium, the kidney regu-lates potassium balance. Urine is the major excretory route in healthy people, with only small amounts lost in the feces and minimal amounts in sweat.
Potassium, sodium, and chloride are the major deter-minants of osmotic pressure and electrolyte balance.
The concentration difference of potassium and sodium across cell membranes is maintained by the Na+/K+-ATPase pump and is critical for nerve trans-mission and muscle function. The physiological importance of potassium in the body covers many systems including cardiovascular, respiratory, diges-tive, renal, and endocrine. In addition, potassium is a cofactor for enzymes involved in inter alia energy metabolism, glycogenesis, and cellular growth and division.
The low concentration of potassium in plasma is tightly regulated. Hypokalemia, however, can result from either excessive uptake of potassium by cells or potassium depletion from the body. Insulin excess, catecholamine increases, Cushing’s disease (excess steroids), diuretics that enhance potassium loss, chronic renal disease, diarrhea, vomiting, and laxative abuse can result in hypokalemia. Low potassium intakes are unlikely to lead to clinical potassium depletion and hypokalemia except during starvation and anorexia nervosa.
The activity of nerves and muscles is affected in potassium depletion, and other clinical sequelae involve cardiac (including cardiac arrest), renal, and metabolic alterations. Potassium supplementation may have a role to play in treating chronic heart failure, and increased potassium intakes can decrease blood pressure via antagonistic metabolic interactions with sodium, resulting in increased sodium excretion, and also via a direct vasodilatory effect. Oral administra-tion of potassium salts has been shown to improve calcium and phosphorus balance, reduce bone resorp-tion and increase the rate of bone formation.
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