Potassium (K⁺) is the major intracellular cation. The total K⁺ content of the body averages 3500 mEq (50 mEq/kg body weight), 90% of which is intracellular. About 8% of the total body K⁺ is in bone and cartilages. Although only 2% of the total body potassium is in the extracellular fluid, its concentration is finely regulated by the flux of K⁺ between the extracellular and intracellular spaces (internal potassium homeostasis). When this concerted balance is offset, however, significant changes occur in serum potassium levels.

Daily minimum requirement of K⁺ is approximately 1600 to 2000 mg (40 to 50 mEq) (40 mg = 1 mEq). Potassium intake varies widely according to the type of diet consumed, age, and race. Thus, 15- to 20-year-olds may consume up to 3400 mg (85 mEq) of K⁺ daily, whereas elderly individuals, especially if they live alone or are disabled and are not eating balanced meals, have low K⁺ intake. People who eat large amounts of fruits and vegetables have a high K⁺ intake, on the order of 8000 to 11,000 mg (200 to 275 mEq) per day.<sup>26 National Research Council   Diet and Health: Implications for Reducing Chronic Disease Risk: Report of the Committee on Diet and Health, Food and Nutrition Board Washington, DC: National Academy Press (1989). 

Cliccare qui per andare alla sezione Riferimenti</sup> Urban whites consume about 2500 mg (62.5 mEq) of K⁺ per day,<sup>17 Khaw K.T., Barrett-Connor E. Dietary potassium and stroke-associated mortality: A 12-year prospective population study N Engl J Med 1987 ;  316 : 235  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> whereas African-Americans are reported to have a low intake of K⁺ on the order of 1000 mg (25 mEq) per day.<sup>12 Grimc Luft F.C., Miller J.Z. , e al. Racial differences in blood pressure in Evans County, Georgia: Relationship to sodium and potassium intake and plasma renin activity J Chronic Dis 1980 ;  33 : 87

Cliccare qui per andare alla sezione Riferimenti</sup> Human milk contains small amounts of K⁺, about 500 mg (12.8 mEq) per liter, whereas cow's milk contains almost three times as much, 1365 mg (35 mEq) per liter.

In a balanced state of body potassium, 80% of potassium intake is excreted by the kidneys, 15% of potassium is excreted by the gastrointestinal tract, and the remaining 5% of potassium is excreted in the sweat. Urinary potassium is for the most part secretory potassium. Distal potassium secretion is regulated by the amount of sodium in the lumina of the distal and collecting tubules, flow of urine in these segments of the nephron, and the aldosterone activity. Serum potassium in and of itself is an important factor in the regulation of aldosterone activity. The kidneys are the major regulator of external potassium homeostasis (or balance); therefore, excessive loss through the kidneys or retention because of loss of excretory function of the kidneys eventually leads to hypokalemia or hyperkalemia.