Hypertension Prevention Trial (HPT) Feasibility Study
Condition: Cardiovascular Diseases; Heart Diseases; Hypertension; Obesity; Vascular Diseases
MeSH terms: Hypertension; Cardiovascular Diseases; Heart Diseases; Vascular Diseases
Study type: Interventional
Phase: Phase 2

Summary: 
      To test the feasibility and the efficacy of nutritional interventions in the primary
      prevention of hypertension in individuals predisposed to the development of hypertension;
      specifically, to test the hypothesis that reduction of weight and/or decreased sodium intake
      in obese individuals, or decreased sodium intake with or without increased potassium intake
      (in men and women, regardless of weight) would prevent the elevation of blood pressure and
      the incidence of hypertension.
    

Detailed description: 
      BACKGROUND:

      The nature of essential hypertension as a mass public health problem throughout the United
      States, and internationally as well, is recognized generally. Prevalence estimates exceed l5
      percent in most adult populations. Further, the results of the Hypertension Detection and
      Follow-up Program (HDFP) demonstrated the efficacy of antihypertensive therapy even at the
      90-l05 mmHg level, which comprises 72 percent of the total hypertensive population. The Joint
      National Committee on the Detection, Evaluation and Treatment of High Blood Pressure
      recommended treatment of mild hypertension by pharmacologic or non-pharmacologic therapy to
      the lowest diastolic pressure consistent with safety and tolerance. The recommendation was
      consonant with the goal blood pressure guidelines for those with baseline pressures from
      90-99 mmHg. Hence, there appeared to be a growing consensus that reduction of blood pressure
      to levels as low as 80 mmHg might be desirable for optimal cardiovascular health. The Joint
      National Committee further recommended that, in young patients with uncomplicated mild
      hypertension, the benefits from pharmacologic therapy must be weighed against the cost,
      inconvenience, and possible side effects. There was, therefore, a growing concern over the
      need for pharmacologic management of hypertension and the public health implications of such
      a course of action. These recommendations toward intervention in mild hypertension set a firm
      basis for the primary prevention of hypertension.

      The association between obesity and elevated blood pressure was widely recognized. Among
      hypertensive individuals, numerous studies had shown that short term weight reduction by
      caloric restriction resulted in a reduction of blood pressure. Results of several reports of
      long-term follow-up of weight reduction efforts indicated that long-term control of weight at
      levels compatible with the objectives of the HPT was feasible. A number of investigators had
      achieved these levels one or more years after treatment despite minimal intervention efforts
      during the follow-up period.

      There was strong circumstantial evidence relating sodium intake to hypertension. Most
      impressive evidence came from the study of the 'low-salt tribes', subsisting on a very low
      sodium intake. They failed to develop hypertension, or even gradual rise of blood pressure
      with age. Many studies published on the effect of lowering sodium intake on blood pressure of
      hypertensive patients had been positive. In one investigation, blood pressure fell
      approximately 9 (systolic)/6 (diastolic) mmHg when sodium intake was reduced from
      approximately l80 to l00 mEq/day. Reduction of sodium intake to a level of 70-l00 mEq/day
      appeared within the capability of most people and maintenance up to a period of two years had
      been indicated with minimal follow-up procedures.

      The role of potassium intake in the development and treatment of hypertension was less clear.
      As noted above, primitive cultures studied epidemiologically had low sodium intakes
      associated with low prevalence and incidence of hypertension but these cultures also consumed
      higher levels of potassium. It has been suggested that the ratio of sodium to potassium may
      be the most important determinant of blood pressure. Hygienic intervention to increase
      potassium intake in free-living populations was the least studied of the procedures used in
      the HPT. Potassium intakes > l00 mEq could be achieved without the use of dietary supplements
      if individuals consumed large quantities of fruits and vegetables. This natural intake could
      also be increased by use of potassium-based baking powder and seasonings.

      The study was carried out by four clinical and two resource centers (a Coordinating Center
      and a Nutrition and Educational Resource Center). It was to be Phase l of a long-term
      intervention trial to determine whether development of hypertension could be prevented in a
      population at special risk. The initial phase of the study was directed towards testing the
      feasibility of the intervention, alternative modes of recruitment, quantification of sodium
      and potassium intake, trends in blood pressure, and the pre-testing of various study
      procedures.

      Each of the four clinical centers recruited 200 or more eligible 25 to 49 year old
      individuals (total 841), either identified through any of a number of multiple community
      sources, or through an index of hypertensive cases. The clinical investigators aided by
      statistical and data processing support from the Data Coordinating Center and intervention
      support through a special Nutrition and Education Resources Center, formed the collaborative
      group to test the working hypothesis. The study protocol was completed in the fall of 1982.
      Recruitment ended September 30, 1983. The three-year follow-up period ended August 1986.
      Analysis of the data ended in December 1988.

      DESIGN NARRATIVE:

      A randomized, non-blind design with three treatment groups (non-obese) or five groups
      (obese), including a no-treatment group in each weight stratum. Intervention methods were
      dietary only, and included sodium restriction, sodium restriction plus potassium
      supplementation (obese and non-obese), weight reduction, and weight reduction plus sodium
      restriction (obese only). This was a pilot study with measures of feasibility including
      recruitment success, dietary adherence, and blood pressure differences among the treatment
      groups.
    

Intervention name(s): diet, sodium-restricted; diet, reducing; potassium
Intervention type(s): Behavioral; Behavioral; Drug
Allocation: Randomized
Primary purpose: Prevention