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increased risk because excess potassium is readily excreted in the urine. Therefore, a Tolerable Upper Intake Level (UL) was not set. However, in individuals in whom urinary excretion of potassium is impaired, a potassium intake below 4.7 g (120 mmol)/day is appropriate because of adverse cardiac effects (arrhythmias) from the resulting hyperkalemia (a markedly elevated serum potassium concentration). Such individuals are typically under medical supervision.

Common drugs that can substantially impair potassium excretion are angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARB), and potassium-sparing diuretics. Medical conditions associated with impaired urinary potassium excretion include diabetes, chronic renal insufficiency, end-stage renal disease, severe heart failure, and adrenal insufficiency. Elderly individuals are at increased risk of hyperkalemia because they often have one or more of these conditions or are treated with one of these medications.

BACKGROUND INFORMATION

Function

The major intracellular cation in the body is potassium, which is maintained at a concentration of about 145 mmol/L of intracellular fluid, but at much lower concentrations in the plasma and interstitial fluid (3.8 to 5 mmol/L of extracellular fluid). Relatively small changes in the concentration of extracellular potassium greatly affect the extracellular:intracellular potassium ratio and thereby affect neural transmission, muscle contraction, and vascular tone.

Physiology of Absorption and Metabolism

In unprocessed foods, potassium occurs mainly in association with bicarbonate-generating precursors like citrate, and to a lesser extent with phosphate. In foods to which potassium is added in processing and in supplements, the form of potassium is potassium chloride. In healthy persons, approximately 85 percent of dietary potassium is absorbed (Holbrook et al., 1984). The high intracellular concentration of potassium is maintained via the activity of the Na+/K+-ATPase pump. Because this enzyme is stimulated by insulin, alterations in the plasma concentration of insulin can affect cellular influx of potassium and thus plasma concentration of potassium.



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