Dietary Patterns, Sodium Intake and Blood Pressure (DASH - Sodium)
Condition: Cardiovascular Diseases; Heart Diseases; Hypertension; Vascular Diseases
MeSH terms: Cardiovascular Diseases; Heart Diseases; Vascular Diseases
Study type: Interventional
Phase: Phase 2

Summary: 
      To compare the effects of three levels of dietary sodium and two patterns of diet (a control
      diet and an intervention diet high in fruits, vegetables, and low fat dairy products and low
      in fat) on blood pressure in individuals with higher than optimal blood pressure or with
      Stage 1 hypertension.. DASH - Sodium built on and extended the results of the NHLBI-initiated
      Dietary Approaches to Stop Hypertension (DASH) study.
    

Detailed description: 
      BACKGROUND:

      High blood pressure, defined as systolic blood pressure greater than or equal to 140 mm Hg or
      diastolic blood pressure greater than or equal to 90 mm Hg, or taking antihypertensive
      medication, affects 24 percent of the United States adult population or about 50 million
      people. Because the risk of cardiovascular disease and stroke increases with increasing blood
      pressure throughout the entire range of blood pressure levels, people with blood pressure
      above the optimal level of 120/80 are at increased risk of disease. Approximately 48 percent
      of the adult population have blood pressure either normal but above optimal levels or have
      Stage 1 hypertension, a prevalence which increases with age. To combat this highly prevalent
      condition, primary prevention through lifestyle modification represents a highly promising
      strategy for public health.

      DASH - Sodium extended research from DASH trial to address several issues of relevance to
      clinical practice and public health and capitalized on the success of DASH by following the
      multicenter outpatient feeding study model. The model permitted a true test of efficacy
      because of high adherence and follow-up rates. In addition, the population studied across
      four geographic areas, encompassing individuals with diastolic blood pressure between 80-95
      mm Hg and systolic blood pressure <160 mm Hg, was broadly representative, thus making the
      results generalizable to a large portion of the United States population.

      DESIGN NARRATIVE:

      The effects on blood pressure of three levels of sodium intake and two dietary patterns were
      compared. The combined impact of sodium reduction with dietary intervention was evaluated as
      a potential non-pharmacologic treatment alternative to drug therapy for stage one
      hypertension or for maintaining normal blood pressure levels. The two dietary patterns were a
      control diet that represented the typical American diet and an intervention diet (DASH diet)
      that was high in fruits, vegetables, included whole grains, poultry, fish, and nuts, and
      reduced in fats, red meat, sweets, and sugar-containing beverages and dairy products. The
      three levels of sodium were higher (current United States intake), intermediate (current
      recommended levels), and lower (potentially optimal levels). Participants were assigned to
      one of the two dietary patterns using a parallel group design and were fed at each sodium
      level using a randomized cross-over design.

      Three eligibility pre-screening visits were followed by a two-week run-in feeding period and
      then a four-week intervention period at each of three sodium levels. During the run-in for
      the intervention feeding periods, all food was provided to participants. They were required
      to attend the clinic for at least one meal per day, five days per week, and to take home food
      to eat for other meals. Each of the four clinics recruited 100 participants. Blood pressure
      was measured once a week during the first of three weeks and five times during the last week.
      During the final feeding period, fasting blood was collected and 24-hour urine collections
      were analyzed for magnesium, potassium. calcium, sodium, and creatinine.

      DASH - Sodium determined, separately by race, gender, and hypertension status: 1) the effects
      on blood pressure of three levels of dietary sodium within the context of both a control diet
      and the DASH diet; 2) the effect on blood pressure of the DASH diet, relative to the control
      diet, at each of the three levels of sodium intake. The study also assessed whether the
      effect on blood pressure of going from higher to lower sodium diets differs for participants
      in the control and DASH diets. Lastly, the study determined whether the blood pressure effect
      associated with reducing sodium from the higher to the intermediate level differs from the
      blood pressure effect associated with reducing sodium from the intermediate to the lower
      level, that is, testing whether the blood pressure effects of sodium are linear across sodium
      levels for each diet.

      Recruitment and screening began in August 1997. The first cohort began the experimental diets
      in January 1998 and the last cohort completed the diets in November 1999. A total of 412
      participants were enrolled into the study. Results were presented at the annual meeting of
      American Society of Hypertension in May 2000.

      The study was renewed under R01HL57114 to to analyze the data of the trial The hypothesis to
      be tested is that genetic makeup modulates the BP effects of DASH diet and reduced sodium
      intake through one or more of the following mechanisms: 1) effects on vascular tone; 2)
      effects on mineralocorticoid regulation of sodium homeostasis; and 3) effects on
      non-classical regulation of sodium homeostasis.
    

Intervention name(s): diet, fat-restricted; diet, sodium-restricted
Intervention type(s): Behavioral; Behavioral
Intervention model: Parallel Assignment
Primary purpose: Prevention