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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
ity and lowers urinary calcium excretion. At higher levels of sodium chloride intake, potassium reduces blood pressure to a greater extent than at lower levels of sodium chloride intake (Whelton et al., 1997). While the relationship of kidney stones with urinary potassium excretion was weak and nonsignificant, the relationship of kidney stones to the urinary sodium: potassium ratio was direct and highly significant (Cirillo et al., 1994). Finally, the hypocalciuric effect of supplemental dietary potassium bicarbonate is also dampened by dietary sodium chloride (Sellmeyer et al., 2002).
Given the interrelatedness of sodium and potassium, the requirement for potassium may well depend on the level of dietary sodium, and the deleterious effects of sodium may be attenuated by higher dietary intakes of potassium. However, data are presently insufficient to set different potassium intake recommendations according to the level of sodium intake, and vice versa. Likewise, data are insufficient to set requirements based on the sodium: potassium ratio.
As previously discussed, sodium chloride raises blood pressure to a greater extent in African-American men than in white men (Morris et al., 1999b; Weinberger, 1996) and the expression of salt sensitivity is modulated by dietary potassium (Morris et al., 1999b; Weinberger et al., 1982). In one trial (Morris et al., 1999b; Figure 5-1), salt sensitivity continued among some of the nonhypertensive African-American men who consumed a high-normal level of potassium (4.7 g [120 mmol]/day). In another study of African Americans, most of whom were nonhypertensive, a higher dietary intake of potassium (6.6 g [170 mmol]/day) as potassium bicarbonate abolished salt sensitivity (Schmidlin et al., 1999).
Available data also suggest that African Americans, compared with their white counterparts, are more sensitive to the blood pressure-reducing effects of increased dietary potassium. A significant reduction in systolic and diastolic blood pressure was seen when African-American individuals, most of whom were nonhypertensive, increased dietary potassium from a level of 1.3 to a level of 3.1 g (33 to 80 mmol)/day (Brancati et al., 1996). In another study that enrolled African-American hypertensive subjects, supplementation with 2.5 g (64 mmol)/day of potassium chloride significantly reduced systolic and diastolic blood pressure (Obel, 1989). However, neither of these trials enrolled white participants, so the extent of blood pressure reduction in African Americans from increased po-