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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
made in the United States (JNC, 1997). The lower level was 1.2 g (50 mmol)/day for 2,100 kcal (Sacks et al., 2001). The average achieved levels of sodium intake, as reflected by 24-hour urinary sodium excretion, were 142, 107, and 65 mmol/day, respectively, corresponding to approximate intakes of 3.3 g, 2.5 g, and 1.5 g, respectively (Sacks et al., 2001). Urinary potassium excretion averaged 79 and 41 mmol/24 hours on the DASH and control diets, respectively, and did not differ by level of sodium intake.
The main results of the DASH-Sodium trial (Sacks et al., 2001) are displayed in Appendix I—Figure I-14 and Tables I-la,b,c. On the control diet (Figure I-14 and Tables I-1a and 1c), reducing sodium intake from the higher (≈ 3.3 g) to the intermediate level (≈ 2.3 g) lowered systolic blood pressure by an average of 2.1 mm Hg (p < 0.001), while further lowering sodium intake from the intermediate to the lower level of sodium (1.2 g) led to an additional systolic blood pressure reduction of 4.6 mm Hg (p < 0.001). On the DASH diet (Figure I-14, Tables I-1a and 1b), corresponding reductions in systolic blood pressure were 1.3 (p < 0.05) and 1.7 mm Hg (p < 0.01), respectively. Hence decreasing sodium intake by approximately 0.92 g (40 mmol)/day caused a greater lowering of blood pressure when the starting sodium intake was at the intermediate level than when it was at a higher intake similar to the U.S. average.
The trial by Sacks and colleagues (2001) also provided an opportunity to assess the impact of sodium reduction in relevant subgroups (Vollmer et al., 2001; see Table 6-14). On the control diet, significant blood pressure reduction was evident in each subgroup. Reduced sodium intake led to greater systolic blood pressure reduction in individuals with hypertension compared with those classified as nonhypertensive, African Americans compared with non-African Americans, and older individuals (> 45 years old compared with those ≤ 45 years old). On the DASH diet, a qualitatively similar pattern was evident; however, some sub-group analyses did not achieve statistical significance, perhaps as a result of small sample size. Comparing the combined effect of the DASH diet with lower sodium with the control diet with higher sodium, the DASH diet with lower sodium reduced systolic blood pressure by 7.1 mm Hg in nonhypertensive persons and by 11.5 mm Hg in individuals with hypertension.
Other key findings emerged related to the dose-response relationship of sodium with blood pressure from the DASH-Sodium trial. First, the blood pressure response to sodium reduction was nonlinear, that is, there was a steeper decline in blood pressure when sodium was reduced from 2.3 g (100 mmol)/day to 1.2 g (50