Effectiveness of the DASH Diet at Reducing High Blood Pressure
Condition: Cardiovascular Diseases; Hypertension; Heart Diseases
MeSH terms: Cardiovascular Diseases; Heart Diseases
Study type: Interventional

Summary: 
      The purpose of this study is to test the effects of the DASH diet in patients with isolated
      systolic hypertension.
    

Detailed description: 
      BACKGROUND:

      The study expands upon the findings of the Dietary Approaches to Stop Hypertension (DASH)
      study, which showed that a dietary pattern emphasizing fruits, vegetables, and low fat dairy
      products and overall reduced in total and saturated fat significantly lowers blood pressure
      (BP). The DASH diet is particularly effective in African Americans and in individuals with
      systolic hypertension. However, it is not known if the DASH diet affects the pathophysiology
      of the hypertensive process. Preliminary data support the possibility that the DASH diet
      interrupts the renin-angiotensin system. This raises the intriguing possibility that the DASH
      diet will favorably impact on cardiovascular and renal hemodynamics in patients with isolated
      systolic hypertension. Therefore, the central hypothesis of this study is that the DASH diet
      affects central aortic stiffness, diastolic relaxation, and renal and vascular reactivity to
      angiotensin II (Ang II) by lowering tissue renin-angiotensin system activity.

      DESIGN NARRATIVE:

      A randomized, crossover design will be used to compare the DASH diet to a control diet as
      defined in the original DASH protocol (NEJM 1997; 336:1117). Fifty-five community-dwelling
      individuals age 20 and older with systolic blood pressure (SBP) 140-179 mmHg and diastolic
      blood pressure (DBP) less than 90 mmHg will enter a 1-week run-in period eating both the
      control and DASH diets for 3-4 days each. Following this, participants will begin two 4-week
      intervention feeding periods receiving either the DASH diet or the control diet in random
      order. Clinical measurements will be taken at the conclusion of each 4-week feeding period.

      Outcome measures: Specific measurements will include peripheral and renal vascular response
      to Ang II infusions, renal blood flow measured by para-aminohippurate (PAH) clearance,
      conduit vessel hemodynamics, and tissue Doppler imaging (TDI). At the end of each
      intervention feeding period, the clinical measurements will be made before and after acute
      administration of captopril, an angiotensin converting enzyme (ACE) inhibitor.

      The study will test whether the DASH diet (1) lowers central aortic stiffness as measured by
      vascular impedance and carotid-femoral pulse wave velocity; (2) improves diastolic relaxation
      as measured by early diastolic myocardial velocities across the mitral valve (Ea); (3)
      vasodilates renal blood flow and enhances vascular responses to Ang II; and (4) affects
      central aortic stiffness, diastolic relaxation, renal blood flow, and renal and vascular
      reactivity to Ang II by altering target tissue responsiveness to Ang II similar to ACE
      inhibition.
    

Intervention name(s): Dietary Approaches to Stop Hypertension (DASH); Control Diet
Intervention type(s): Behavioral; Behavioral
Intervention description(s): 4 week feeding intervention; 4 week feeding intervention
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Prevention