The latest Clinical Therapeutics article, Dietary Therapy in Hypertension, comes from Drs. Frank Sacks and Hannia Campos at the Harvard School of Public Health.
Among most populations in developed countries, the prevalence of hypertension increases dramatically with age; in the United States it rises from about 10% in persons 30 years of age to 50% in those 60 years of age. Morbidity increases progressively among persons whose blood pressure is above 115/75 mm Hg.
• What was the efficacy of the original DASH diet?
In the original DASH trial, 459 adults whose systolic blood pressure was less than 160 mm Hg and whose diastolic blood pressure was 80 to 95 mm Hg, 133 of whom had hypertension, were randomly assigned to a control diet typical of the average U.S. diet, a diet rich in fruits and vegetables, or a combination diet rich in fruits, vegetables, and low-fat dairy products and relatively low in saturated and total fat. Sodium intake and body weight were maintained at constant levels. After 8 weeks, among the participants with hypertension, the diet rich in fruits and vegetables reduced systolic and diastolic blood pressure by 7.2 and 2.8 mm Hg more, respectively, than the control diet (P<0.001 and P=0.01, respectively). The combination diet resulted in comparable reductions (11.4 and 5.5 mm Hg, respectively, as compared with the control diet; P<0.001 for each).
• How does weight loss contribute to the antihypertensive effect of the DASH diet?
The effect of adding weight loss to the DASH diet was evaluated in 144 adults in the ENCORE study. Participants were randomly assigned to a control diet, to the DASH diet alone, or to a reduced-calorie modification of the DASH diet. At 4 months, blood pressure was reduced by 3.4/3.8 mm Hg in the control group, by 11.2/7.5 mm Hg in the group given the DASH diet alone (P<0.001 for both systolic and diastolic pressures as compared with the control diet), and 16.1/9.9 mm Hg with the DASH diet plus weight management (P=0.02 for systolic blood pressure and P=0.05 for diastolic blood pressure as compared with the DASH diet alone).
Morning Report Questions
Q: How does salt restriction lead to a lower blood pressure in patients with essential hypertension?
A: In essential hypertension sodium excretion is impaired. It is hypothesized that in most cases essential hypertension is a genetic disorder involving many individual genes, each of which influences the body’s handling of sodium to varying degrees and becomes expressed in the context of an unhealthful dietary environment, particularly one characterized by excessive intake of salt. Reductions in dietary salt lessen the amount of sodium the kidney has to excrete to restore normal blood volume. Aortic and carotid artery compliance is significantly improved in older patients with hypertension when sodium intake is reduced. Reduction in sodium intake also improves arterial vasodilation.
Q: What is the recommended dietary approach to managing hypertension?
A: The authors recommend the American Heart Association’s guidelines for cardiovascular health and the dietary management of hypertension. These guidelines endorse foods and approaches to diet similar to those included in the DASH diet and cite intake of 65 mmol, or 1.5 g, of sodium per day as optimal. In addition, a target BMI of less than 25 is recommended. Finally, the guidelines recommend no more than two alcoholic drinks per day for men and one for women and people of lighter weight.
Table 1. Recommended Weekly and Occasional Food Purchases for One Person Following a Healthful Diet Containing 2100 kcal and 1500 mg of Sodium per Day.