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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
leagues (1979b) tested the broadest range of sodium intake (0.23 to 34.5 g [10 to 1500 mmol]/day of sodium), albeit in just 14 individuals. Only two trials (Ferri et al., 1996; Sacks et al., 2001) enrolled over 50 persons, but the trial by Ferri and colleagues only enrolled hypertensive individuals. The trial by MacGregor and coworkers (1989) is a well-controlled trial that documented a direct, progressive relationship between sodium intake and blood pressure, but the trial enrolled only 20 individuals, all of whom were hypertensive. The trial by Johnson and colleagues (2001) tested increasing levels of sodium intake from baseline by giving four different levels of sodium chloride (range of total intake: 0.9 g [40 mmol]/day to 14.8 g [340 mmol]/day) in 46 individuals, 60 years of age and older; in each blood pressure stratum (nonhypertension, isolated systolic hypertension, and systolic-diastolic hypertension), there were significant, progressive, dose-response relationships between sodium intake and blood pressure.
A detailed overview of the trial by Sacks and colleagues (2001) is warranted in view of its size, duration, and other design features. This trial, termed the DASH-Sodium study, was a feeding study designed to test the effects on blood pressure of three levels of sodium intake (an average of 1.2, 2.3, and 3.5 g [50, 100, and 150 mmol]/day of sodium/2,100 kcal) separately in two distinct diets—the DASH (Dietary Approaches to Stop Hypertension) diet and a control diet (See Figure I-14 in Appendix I and corresponding Tables I-1a, b, c). The DASH diet is rich in fruits, vegetables, and low-fat dairy products and is reduced in saturated and total fat; accordingly, it is rich in potassium, magnesium, and calcium (corresponding to the 75th percentile of U.S. intake) (Appel et al., 1997). In contrast, the potassium, magnesium, and calcium levels of the control diet corresponded to the 25th percentile of U.S. intake, while its macronutrient profile and fiber content were similar to average U.S. consumption (Appel et al., 1997; Craddick et al., 2003) (see Table 6-9). A total of 412 participants enrolled; of these, 41 percent were hypertensive, 40 percent were white, and 57 percent were African American (Sacks et al., 2001).
Study participants were randomly assigned to the control or DASH diet, and, within their assigned diet, participants ate higher, intermediate, and lower sodium levels, each for 30 days in random order. By design, in the 2,100-kcal version of the diets, the higher sodium level was 3.5 g (150 mmol)/day of sodium. Thus the higher sodium level reflected typical U.S. adult consumption. The intermediate sodium level was 2.3 g (100 mmol)/day for the 2,100-kcal version, reflecting the upper limit of various recommendations