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.
