The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium): Rationale and Design

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Abstract

The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium) is a multicenter, randomized trial comparing the effects of 3 levels of sodium intake and 2 dietary patterns on blood pressure among adults with higher than optimal blood pressure or with stage 1 hypertension (120–159/80–95 mm Hg). The 2 dietary patterns are a control diet typical of what many Americans eat, and the DASH diet, which, by comparison, emphasizes fruits, vegetables, and low-fat dairy foods, includes whole grains, poultry, fish, and nuts, and is reduced in fats, red meat, sweets, and sugar-containing beverages. The 3 sodium levels are defined as higher (typical of current US consumption), intermediate (reflecting the upper limit of current US recommendations), and lower (reflecting potentially optimal levels). Participants are randomly assigned to 1 of the 2 dietary patterns using a parallel group design and are fed each of the 3 sodium levels using a randomized crossover design. The study provides participants with all of their food during a 2-week run-in feeding period and three 30-day intervention feeding periods. Participants attend the clinic for 1 meal per day, 5 days per week, and take home food for other meals. Weight is monitored and individual energy intake adjusted to maintain baseline weight. The primary outcome is systolic blood pressure measured at the end of each intervention feeding period. Systolic blood pressure is compared across the 3 sodium levels within each diet and across the 2 diets within each sodium level. If effects previously observed in clinical trials are additive, sodium reduction and the DASH diet together may lower blood pressure to an extent not as yet demonstrated for nonpharmacologic treatment. The DASH-Sodium results will have important implications for the prevention and treatment of high blood pressure. J Am Diet Assoc. 1999;99(suppl):S96–S104.

Section snippets

Research Questions and Rationale

The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium) is an ongoing multicenter, randomized controlled feeding trial designed to evaluate the separate and combined effects of sodium reduction and the DASH diet in reducing blood pressure among adults with higher than optimal blood pressure or with stage 1 hypertension (120 to 159/80 to 95 mm Hg). The study began in February 1997 and will be completed by February 2001. The sodium levels to be tested include higher intake, consistent

Methods

DASH-Sodium is an investigator-initiated multicenter clinical trial supported by the National Heart, Lung, and Blood Institute (NHLBI). Collaborating on this trial are scientists from 4 clinical centers, a coordinating center, a central food analysis laboratory, a central blood and urine analysis laboratory, and NHLBI. After eligibility screening, all participants enter a 2-week run-in feeding period during which they eat the control dietary pattern at the higher sodium level. They are then

Discussion

The DASH-Sodium study will determine the independent blood pressure–lowering effects of sodium reduction and of the DASH diet (which emphasizes fruits, vegetables, and low-fat dairy products, includes whole grains, poultry, fish, and nuts, and is reduced in fats, red meat, sweets, and sugar-containing beverages) in persons with higher than optimal blood pressure or stage 1 hypertension. Specifically, DASH-Sodium will determine the effect of sodium intake at 3 clinically relevant levels in the

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