use of a potassium-containing salt substitute while under treatment for chronic diseases (Haddad and Strong, 1975; Ray et al., 1999; Snyder et al., 1975) (see Table 5-13). These individuals had some type of heart or renal disease and therefore were taking other medications, including ACE inhibitors. The potassium-containing salt substitute might have been prescribed to reduce sodium chloride intake, to replace diuretic-induced potassium losses, or both. Such patients are at risk both for hypokalemia and hyperkalemia and therefore require close medical supervision.
In otherwise healthy individuals (that is, individuals without impaired urinary potassium excretion from a medical condition or drug therapy), there have been no reports of hyperkalemia resulting from acute or chronic ingestion of potassium naturally occurring in food. Hyperkalemia might theoretically occur if the capacity of the normal kidney to excrete a potassium load is exceeded. The maximum excretion rate of normal kidneys after adaptation to high levels of intake has been estimated to be approximately 31.3 g (800 mmol)/day for adults (Berliner, 1961), a level that would be difficult to achieve from food alone. Gastrointestinal discomfort has been reported with some forms of potassium supplements, but not with potassium from foods.
Adults. In otherwise healthy individuals (i.e., individuals without impaired urinary potassium excretion from a medical condition or drug therapy), there is no evidence that a high level of potassium from foods has adverse effects. Therefore, a Tolerable Upper Intake Level (UL) for potassium from foods is not set for healthy adults.
In contrast, supplemental potassium can lead to acute toxicity in healthy individuals. Also, chronic consumption of a high level of potassium can lead to hyperkalemia in individuals with impaired urinary potassium excretion (see later section, “Special Considerations”). Hence, supplemental potassium should only be provided under medical supervision because of the well-documented potential for toxicity.
Infants and Children. Almost all of the potassium that appears in urine is secreted by the last half of the distal tubule (Schultze, 1973).