DASH diet combined with low sodium intake leads to greater BP-lowering in patients with higher baseline level
Effects of Sodium Reduction and the DASH Diet in Relation to Baseline Blood Pressure
Background
The Dietary Approaches to Stop Hypertension (DASH) and the DASH-Sodium trials showed that a DASH diet rich in fruits, vegetable, and low-fat dairy products, with reduced saturated fat and cholesterol, as well as a diet with low sodium, lowered SBP and DBP [1,2]. Therefore, the DASH diet and sodium reduction are recommended for all adults with pre-hypertension or stage 1 hypertension, as well as for the general population [3]. It is not known whether the effects of the DASH diet or sodium reduction differ by BP severity.
The DASH-Sodium trial was a randomized DASH follow-up trial, in which the effects of consuming 3 different sodium levels in combination with either the DASH diet or a typical American control diet were investigated. The control diet included potassium, magnesium, and calcium intakes at the 25th percentile, and average macronutrient profile of the U.S. population, and the DASH diet emphasized whole grains, poultry, fish, and nuts, and was reduced in red meat, sweets, and sugar-containing beverages [2].
Participants received each of 3 sodium levels at 2100 kcal:
- low (50 mmol or 1150 mg)
- medium (100 mmol or 2300 mg)
- high (150 mmol or 3450 mg), reflecting the average sodium intake in the U.S.
All meals and snacks were provided to participants, who underwent a 2-week run-in period, during which they ate the high sodium-control diet. They were then randomized to either the DASH or the control diet and consumed low, medium or high sodium levels, each for 30 days. The order of sodium assignment was randomized, following a cross-over design.
Individuals aged ≥22 years, with SBP of 120 to 159 mmHg and DBP of 80 to 95 mmHg were included in the study. Baseline SBP was classified in strata of <130, 130-139, 140-149, and ≥150 mmHg. Baseline DBP was classified in strata of <80, 80-84, 85-89, and ≥90 mmHg.
Main results
- The reduction of sodium intake from high to low levels in the control arm was associated with reductions in SBP of -3.20 mmHg (95%CI: -4.96 to -1.44), -8.56 mmHg (95%CI: -10.70 to -6.42), -8.99 mmHg (95%CI: -11.21 to -6.77), -7.04 mmHg (95%CI: -12.92 to -1.15) in the respective strata of baseline SBP . The trend across strata was statistically significant (P=0.004).
- The reduction of sodium intake from high to low levels in the DASH diet group, was associated with reductions in SBP of -0.88 mmHg (95%CI: -2.07 to 0.30), -3.29 mmHg (95%CI: -4.71 to -1.88), -4.90 mmHg (95%CI: -7.25 to -2.55), -10.41 mmHg (95%CI: -15.54 to -5.28) in the SBP strata. This trend was also statistically significant (P<0.001).
- During the high sodium intake period, the DASH diet compared with the control diet significantly changed SBP by -4.47 mmHg (95%CI: -6.64 to -2.29), -4.26 mmHg (95%CI: -6.72 to -1.80), -4.72 mmHg (95%CI: -8.25 to -1.19), -10.63 mmHg (95%CI: -18.86 to -2.41) in the baseline SBP strata. There was no significant trend across strata in this case (P=0.66).
- During the low sodium intake period, the DASH diet compared with the control diet changed SBP by: -2.36 mmHg (95%CI: -4.61 to -0.11), 0.92 mmHg (95%CI: -1.47 to 3.31), -0.55 mmHg (95%CI: -4.03 to 2.93), -14.13 mmHg (95%CI: -25.61 to -2.64) in strata of baseline. There was no significant trend across strata in this case either (P=0.29).
- Compared with the high sodium-control diet, the low sodium-DASH diet lowered SBP by -5.30 mmHg (95%CI: -7.66 to -2.94), -7.48 mmHg (95%CI: -10.11 to -4.84), -9.70 mmHg (95%CI: -13.34 to -6.06), -20.79 mmHg (95%CI: -30.88 to -10.69) in baseline SBP strata. There was evidence of a trend for greater reduction in SBP across strata of higher baseline SBP (P for trend <0.001).The pattern of DBP change by baseline DBP was almost identical to that of SBP.
Conclusion
The combination of low sodium intake and the DASH diet was associated with substantially greater reductions in SBP among participants with a higher SBP at baseline, compared with the combination of high sodium intake and the control diet. In adults with pre-hypertension, stage I hypertension, and baseline SBP ≥150 mmHg, the combination of the DASH diet with low sodium intake can achieve substantial (>20 mmHg) BP reductions. These findings confirm the importance of lifestyle interventions among adults with uncontrolled SBP.
Editorial comment
In their editorial article [4], Wang and Gupta characterize the DASH-Sodium trial results as intriguing, since Juraschek et al. showed that the combined DASH-low sodium diet has favorable effects comparable to or exceeding pharmacological BP-lowering monotherapy in prior trials. Moreover, they discuss important open questions related to the association between sodium intake and BP-levels, including the ideal amount of sodium intake for the general population, the underlying pathophysiologic mechanisms that lead to lower BP with lower sodium intake, as well as the issue of salt-sensitivity differences between individuals. The authors conclude as follows: ‘The DASH-Sodium trial was a landmark study that continues to be highly informative. Nonetheless, questions remain regarding how diet and sodium influence blood pressure and how to sustain dietary modifications at a reasonable cost on a broad scale. The DASH-low sodium diet is an important foundation to offer patients, but it is not enough to solve the global hypertension problem. Public policy to regulate mineral and nutrient content in processed foods, programs to promote healthy diet and physical activity, and deeper mechanistic understanding of how salt modulates blood pressure are just a few of the steps needed to reduce the global burden of hypertension.’
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