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to the usual diet. This regimen induced a highly significant reduction in the occurrence of kidney stones. The stone formation rate was significantly lower in the potassium citrate group than in the control group (0.1 stone/patient-year versus 1.1 stones/patient-year, p < 0.001). Total urinary excretion of potassium in the 18 subjects in the potassium citrate group averaged 105 mmol (4.1 g)/day after 36 months, compared with their baseline average of 61 mmol (2.4 g)/day (Barcelo et al., 1993). While not directly measured, it is thus assumed that 2.4 g (61 mmol) would have been present in the diets consumed, for a total intake with the supplement of around 3.6 to 4.7 g (90 to 120 mmol). Similar results have been recorded in uncontrolled studies of potassium citrate (Pak and Fuller, 1986; Pak et al., 1985, 1986; Preminger et al., 1985).

Overall, evidence from several prospective observational studies and one clinical trial supports the use of kidney stones as an outcome criterion to establish dietary adequacy of potassium. However, additional trials are clearly warranted.

Prevention of Impaired Pulmonary Function

Changes in the extracellular and intracellular concentration of electrolytes, including potassium, can influence the contraction and relaxation of bronchial smooth muscles (Souhrada and Souhrada, 1983, 1984). The limited studies on potassium intakes and pulmonary function in adults have yielded mixed results, with one study showing increased airway responsiveness to chemicals that induce constriction of the airways (e.g., histamine) with decreasing urinary potassium excretion (Tribe et al., 1994), while no relationship was found between potassium intake and bronchial responsiveness or respiratory symptoms in adults in a second study (Zoia et al., 1995).

As in adults, data on children are limited. Increased bronchial responsiveness with higher levels of potassium excretion was observed in the children studied (Pistelli et al., 1993), while in another study, low potassium intakes were associated in children with lower pulmonary function (e.g., expiratory volume, flow, and capacity) (Gilliland et al., 2002).

FACTORS AFFECTING POTASSIUM REQUIREMENTS

Climate and Physical Activity

Increased losses of potassium, primarily via sweat, can occur with heat exposure and exercise. Thus the requirement for potassium



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