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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
spinal BMD substantially increased over a period of time (which varied from approximately 1 to 10 years) in which an age-related decrease might otherwise have occurred (Pak et al., 2002). In normal adults, potassium bicarbonate has been demonstrated to be hypocalciuric, whereas potassium chloride has not (Lemann et al., 1991). This reflects not only the direct acidosis-countering effect of the bicarbonate component of potassium bicarbonate, but also the capacity of potassium (Brunette et al., 1992) and bicarbonate (Peraino and Suki, 1980) to jointly enhance the renal reclamation of calcium.
Relationship with Sodium
The dietary intake of sodium chloride is an important determinant of urinary calcium excretion and calcium balance. The urinary excretion of calcium is well documented to vary directly with that of sodium (see Table 6-19 in Chapter 6). There is evidence that reducing dietary sodium chloride can induce beneficial effects on bone by reducing the renal loss of calcium and increasing its retention (Devine et al., 1995; Matkovic et al., 1995). However, on a mole-for-mole basis, the hypocalciuric effect of orally administered potassium overrides the hypercalciuric effect of dietary sodium (Morris et al., 1999b; Sellmeyer et al., 2002). In a metabolically controlled outpatient study of normal men fed a diet deficient in potassium (1.2 g [30 mmol]/day), increasing dietary sodium chloride from 1.8 g (30 mmol)/day to 14.6 g (250 mmol)/day induced a 50 percent increase in urinary calcium that supplemental potassium bicarbonate either reversed or abolished, depending on whether dietary potassium was increased to 2.7 or 4.7 g (70 or 120 mmol)/day (Morris et al., 1999b). In an outpatient study of postmenopausal women, the hypercalciuric effects of sodium loading with 5.2 g (225 mmol)/day sodium and a concomitant increase in bone resorption, as indicated by biochemical markers, was abolished by supplying 3.5 g (90 mmol)/day of dietary potassium as potassium citrate, a supplement that increased urinary potassium to 141 mmol (5.5 g)/day (Sellmeyer et al., 2002).
Prevention of Kidney Stones
In several studies, an increased dietary intake of potassium has been associated with a reduced risk of kidney stones. The occur-