Trials of Hypertension Prevention (TOHP)

BACKGROUND:

High blood pressure affects between 15 and 30 percent of the adult population in the United States, and is a major contributor to some of the leading causes of death including coronary artery and cerebrovascular diseases. A substantial body of evidence from both population and laboratory studies indicates that a number of dietary and lifestyle factors are associated with the chronic and progressive increase in blood pressure with age, commonly observed in populations of industrialized countries. There are also an increasing number of reports of important reductions in blood pressure in persons with hypertension following treatment with a number of different non-pharmacological interventions. These observations have led to interest in the possibility of the primary prevention of hypertension through non-pharmacological intervention on factors related to the development of high blood pressure.

In 1979, the main results of the NHLBI-supported Hypertension Detection and Follow-up Program (HDFP), then the largest of the randomized clinical trials of antihypertensive drug treatment, were reported. This trial compared the effects of intensive systematic Stepped-Care drug treatment with Referred-Care in the community. These results confirmed findings of earlier and subsequently reported placebo-controlled trials that effective blood-pressure lowering in hypertensive individuals reduces the occurrence of stroke, congestive heart failure, and other complications of hypertension, and for the first time demonstrated a significant reduction of total mortality. The implications of the findings regarding recommendations for long-term drug treatment for tens of millions of Americans led several groups of investigators to consider alternative approaches to the control of hypertension. To the concerns of these clinicians about drug-related symptoms and economic costs were added additional questions regarding the safety of common antihypertensive agents in some hypertensive subgroups, based on the results of the Multiple Risk Factor Intervention Trial and on other evidence.

A number of small to moderate-sized randomized clinical trials of non-pharmacologic intervention in hypertension have been initiated during the past 5 years with NHLBI support. The Hypertension Prevention Trial (HPT) was the largest program studying the effectiveness of intervening in a non-hypertensive population. The HPT was a feasibility study to establish the ability to enroll in sufficient numbers men and women with diastolic blood pressure of 78-89 mm Hg; to determine if dietary intervention alone could achieve sustained weight reduction, and/or a decrease in sodium intake, or an increase in potassium intake along with sodium reduction in these subjects; and to study the effects of the interventions on blood pressure. If feasibility were demonstrated, the plan was to conduct a full-scale trial with incidence of frank hypertension as the outcome measure.

The HPT achieved its feasibility goals regarding recruitment of participants and weight reduction, but not for dietary sodium reduction and potassium increase. Some of the other dietary trials among non-hypertensive subjects have also achieved relatively small sodium changes (20-25 percent); a few have produced much larger changes, but only with short-term follow-up. Other experience has also shown that it is difficult to increase potassium intake by dietary means alone.

The importance of further work in this area has meanwhile been reinforced by conclusions of several expert groups convened by NHLBI. These have included the participants in the 1984 NIH Workshop on Nutrition and Hypertension and the 1984 Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure, whose report addressed in some detail non-pharmacologic intervention and primary prevention.

DESIGN NARRATIVE:

Phase I was a pilot study to test the feasibility of providing and obtaining compliance with selected nutritional-behavioral, non-pharmacologic interventions and to measure the short-term effectiveness of the interventions on reducing or preventing an increase in diastolic blood pressure. Ten clinical centers, and a coordinating center, which included two central laboratories and a nutrient data center, participated. Each clinic tested a subset of the interventions. The lifestyle arm of the trial, which included weight loss, sodium restriction, and stress management, had an open design with untreated controls. The two-stage supplement arm of the trial, which tested magnesium and calcium in Stage I, and fish oil and potassium in Stage II, was double-blinded and placebo-controlled. Three clinics tested only lifestyle interventions, two tested only supplements, and five participated in both arms of the trial. Recruitment began in August 1987 and randomization was completed by October 1988. Endpoint data collection was completed in January 1990. The average follow-up was approximately 18 months.

Phase II had a 2x2 factorial design to test the effectiveness of weight loss and sodium restriction alone and in combination in reducing blood pressure and decreasing the incidence of definite hypertension. Lifestyle interventions were administered through counseling sessions at each center. Blood pressure, weight, body mass index, skin fold thickness, and urine electrolytes were measured at baseline and at six month intervals for a minimum of 36 months. Recruitment began at the end of 1990 and was completed in March 1992. Intervention and follow-up were completed in March 1995. Data analysis continued through June 1998 under U01-HL-37852, the coordinating center.

The main results were presented at the 1995 American Heart Association Scientific Sessions. The Phase II main results paper was published in March 1997.

The study completion date listed in this record was obtained from the "End Date" entered in the Protocol Registration and Results System (PRS) record.

Men and women, ages 30 to 54, with high normal diastolic blood pressure between 83 and 89 mm Hg.

Subjects were mildly obese.