Trials of Hypertension Prevention (TOHP)

Objectives

Phase I of TOHP (TOHP I) was designed to test the short-term feasibility and efficacy of seven nonpharmacologic interventions in persons with high normal BP. These interventions included the lifestyle interventions of weight loss, sodium reduction, and stress management, and the nutritional supplement interventions of calcium, magnesium, potassium and fish oil.

Phase II of TOHP (TOHP II) was designed to test the efficacy of interventions to promote weight loss, sodium reduction, and the combination of weight loss and sodium reduction in decreasing diastolic BP, systolic BP, and the incidence of hypertension during a 3- to 4-year follow-up period in moderately overweight men and women with a high-normal level of diastolic BP.

Background

Phase I: As much as one-third of cardiovascular disease attributable to an above-optimal BP level occurs in the nonhypertensive portion of the distribution, providing impetus for directing prevention efforts at high normal levels of BP. Epidemiologic studies have identified several dietary and other factors related to lifestyle as possible determinants of BP levels. As of the mid-1980s, few trials had reported any results in subjects with BP levels in the nonhypertensive range, and almost none included long-term follow-up. The goals of Phase I of TOHP were to (1) test the short-term effect on BP of selected nutritional and behavioral interventions, and (2) to determine the feasibility of a long-term clinical trial of methods for reducing the incidence of hypertension.

Phase II: Between 30% and 40% of all BP-related CVD events occur in individuals with an average BP below currently defined hypertensive levels but above the optimal level. A large body of information from observational studies has identified several determinants of elevated BP. The corresponding interventional data are less plentiful and much of what is available reflects experience in small studies with relatively short periods of follow-up. The initial phase of TOHP (TOHP I) tested the feasibility and efficacy of 3 separate lifestyle interventions (weight loss, dietary sodium reduction, and stress management) and 4 separate nutritional supplement interventions (calcium, magnesium, potassium, and fish oil). The weight loss and sodium reduction groups, but not the other groups, demonstrated significant decreases in both systolic and diastolic BP. The second phase of TOHP was designed to test the effect of the two most promising interventions over a longer period of follow-up.

Subjects

Phase I: Subjects were BP eligible if their mean diastolic BP averaged over the three screening visits with three measurements per visit was in the range 80-89 mmHg, and they had not taken antihypertensive medication within the past two months. The entry weight criterion for the weight loss intervention only was a BMI in the range 26.08 to 36.14 for men and 24.26 to 36.14 for women. Randomization began in September of 1987, and ended in October of 1988. Of the 2,182 randomized participants, the average age at randomization was 43 years, 70% were male, 82% were white, and 15% were black. Collection of final visit data occurred throughout 1989, and ended on January 12, 1990.

Phase II: Participants were 30-54 years of age, with a body mass index representing 110-165% of desirable body weight. BP was measured at each of 3 screening visits with 3 measurements per visit. Eligible subjects had an average diastolic BP in the range 83-89 mmHg, with systolic BP <140 mmHg, and were not on antihypertensive medication. A total of 2,382 participants were randomized into the trial. Average age at baseline was 44 years, 66% of participants were male, and 21% were minority.

Conclusions

Phase I: The weight reduction intervention produced an average weight loss of 3.9 kg, a diastolic BP change of -2.3 mm Hg, and a systolic BP change of -2.9 mm Hg. The sodium reduction intervention lowered urinary sodium excretion by 44 mmol/24 h, diastolic BP by 0.9 mm Hg, and systolic BP by 1.7 mm Hg. Neither stress management nor nutritional supplements reduced diastolic BP significantly. The weight reduction and sodium reduction interventions were the most effective of those tested for reducing BP in normotensive persons (JAMA 1992;267:1213-20). The long-term effects of these require further evaluation.

Phase II: At six months, compared to usual care, BP decreased 3.7/2.7 mm Hg in the weight loss group, 2.9/1.6 mm Hg in the sodium reduction group, and 4.0/2.8 mm Hg in the combined group. At 36 months, BP decreases remained greater in the active intervention groups than in the usual care group (weight loss, 1.3/0.9 mm Hg; sodium reduction, 1.2/0.7 mm Hg; combined, 1.1/0.6 mm Hg). The incidence of hypertension was significantly less in each active intervention group than in the usual care group (Arch Intern Med 1997: 157:657-667). In overweight adults with high-normal BP, weight loss and reduction in sodium intake, individually and in combination, were effective in lowering systolic and diastolic BP, especially in the short-term. Although the effects on average BP declined over time, reductions in hypertension incidence were achieved.

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