ASH position paper: Dietary approaches to lower blood pressure
Introduction
Worldwide, elevated blood pressure (BP) is the leading cause of death, even exceeding deaths attributable to smoking and elevated cholesterol. This finding reflects the fact that BP is a strong, consistent, continuous, independent, and etiologically relevant risk factor for cardiovasculardisease(CVD)-renaldisease. Importantly, there is no evidence of a threshold -- the risk of CVD increases progressively throughout the range of usual BP including the nonhypertensive and prehypertensive ranges. Nearly a third of BP-related deaths from coronary heart disease occur in individuals who are not hypertensive.
Elevated BP is extraordinarily common. According to the most recent national survey data in the United States (1999-2004), 32% of adult Americans have hypertension, and roughly another third have prehypertension. Prehypertensive individuals are at high-risk for developing hypertension and carry an excess risk of CVD compared with nonhypertensive individuals. On average, African Americans have higher BP than non-African Americans, as well as an increased risk of BP-related complications, particularly stroke and kidney failure. According to recent survey data, the prevalence of hypertension is increasing, while control rates remain low (<40%) but are improving slightly.
A cardinal feature of the BP epidemic is the age-related rise in BP. In adults, systolic BP (SBP) rises by approximately 0.6 mm Hg per year. Among children, ages 1 to 18 years, the average rise in SBP per year is considerably steeper, approximately 1.5 mm Hg per year in girls and 1.9 mm Hg per year in boys. As a result of the age-related rise in BP, hypertension typically occurs in middle- and older-aged adults. Among adults, 50 years and older, the lifetime risk of becoming hypertensive is 90%. Elevated BP results from environmental and genetic factors and interactions among these factors. Available evidence indicates that dietary factors have a prominent and likely predominant role. In individuals without hypertension, dietary changes reduce BP and prevent hypertension, thereby lowering the risk of BP-related complications. Indeed, even a small reduction in BP, if applied to an entire population, could have a tremendous beneficial impact. It has been estimated that a 3 mm Hg reduction in SBP should lead to an 8% reduction in mortality from stroke and a 5% reduction in mortality from coronary heart disease. In stage I hypertension, dietary changes can serve as initial therapy before the start of BP medication. Among hypertensive individuals who are already taking medication, dietary changes can further lower BP and facilitate stepdown of drug therapy. In general, the extent of BP reduction is greater in hypertensives than in nonhypertensives.
The purpose of this position paper is to summarize evidence on the effects of diet-related factors that lower BP and to present recommendations for health care providers. Supportive evidence includes results from animal studies, cross-cultural studies, within-population observational studies, trials with BP as an outcome variable, and more recently some trials with clinical outcomes. The recommendations in this document are based on, and therefore similar to, those expressed in policy documents issued by the American Heart Association16and the federal government.
Scientific Background
Recommended Dietary Approaches that Lower BP
Weight Loss
Weight is directly associated with BP. The importance of this relationship is evident by the high and increasing prevalence of overweight and obesity world-wide. Approximately 65% of U.S. adults are classified as overweight or obese and more than 30% of U.S. adults are obese. Over the past decade, the prevalence of overweight in U.S. children and adolescents has increased, as have levels of BP.
With rare exception, trials have documented that weight loss lowers BP. Importantly, reductions in BP occur without attainment of a desirable body weight. In one meta-analysis of 25 trials, mean systolic diastolic BP (DBP) reductions were 4.4 3.6 mm Hg from an average weight loss of 5.1 kg. Within-trial, dose response analyses and prospective observational studies23have documented that greater weight loss leads to greater BP reduction. Other trials have documented that modest weight loss, with or without sodium reduction, can prevent hypertension by approximately 20% among prehypertensive individuals and can facilitate medication stepdown and drug withdrawal. Nonetheless, the long-term effects of sustained weight loss on BP are uncertain, with some studies suggesting attenuated BP reduction over time.
In aggregate, available data strongly support weight reduction as an effective approach to prevent and treat elevated BP. In view of the well-recognized challenges of maintaining weight loss, public health efforts to prevent overweight and obesity are critically important.
Dietary Patterns
Vegetarian Diets
Vegetarian diets are associated with reduced BP. In industrialized countries, vegetarians have markedly lower BP than nonvegetarians. In observational studies, vegetarians also experience a blunted rise in BP with age. Several aspects of a vegetarian lifestyle might lower BP, including nondietary factors, established dietary risk factors, and other aspects of a vegetarian diet (eg, high-fiber, no meat). Some trial evidence suggests that established dietary risk factors and nondietary factors are not fully responsible for the BP-lowering effects of vegetarian diets and that other aspects of vegetarian diets lower BP. Specifically, in 2 trials, one in nonhypertensives65and another in hypertensives, lactoovovegetarian diets reduced SBP by approximately 5 mm Hg but had equivocal effects on DBP.
DASH-Style Dietary Patterns
The effects of modifying whole dietary patterns have been investigated in several randomized feeding studies that tested either the original DASH diet or variants. The DASH diet emphasizes fruits, vegetables, and low fat dairy products; includes whole grains, poultry, fish, and nuts; and is reduced in fats, red meat, sweets, and sugar-containing beverages. Accordingly, it is rich in potassium, magnesium, calcium, and fiber, and reduced in total fat, saturated fat, and cholesterol; it is also slightly increased in protein.
It is likely that several aspects of the DASH diet, rather than just one nutrient or food, reduced BP. Among all participants, the DASH diet significantly lowered mean SBP DBP by 5.5 3.0 mm Hg. A second diet, that emphasized just fruits and vegetables, also lowered BP but to a lesser extent, about half of the effect of the DASH diet. The DASH diet lowered BP in all major subgroups (men, women, African Americans, non -- African Americans, hypertensives, and nonhypertensives). However, the effects of the DASH diet in African Americans (SBP DBP reductions of 6.9 3.7 mm Hg) were significantly greater than corresponding effects in non-African Americans (3.3 2.4 mm Hg). The effects in hypertensives (SBP DBP reductions of 11.6 5.3 mm Hg) were substantial and significantly greater than corresponding effects in nonhypertensives (3.5 2.2 mm Hg). In a subsequent trial, the DASH diet significantly lowered BP at each of 3 sodium levels. A third trial, OmniHeart, compared 3 variants of the DASH diets (a diet rich in carbohydrate [58% of total calories], a second rich in protein [about half from plant sources], and a third diet rich in unsaturated fat [predominantly monounsaturated fat]). In several respects, each diet was similar to the DASH diet -- each was reduced in saturated fat, cholesterol, and sodium, and rich in fruit, vege, fiber, and potassium at recommended levels. While each diet lowered SBP, substituting some of the carbohydrate (approximately 10% of total kcal) with either protein (about half from plant sources) or with unsaturated fat (mostly monounsaturated fat) further lowered BP. The original DASH diet, as well as the diets studied in the OmniHeart trial, are safe and broadly applicable to the general population. However, because of their high potassium, phosphorus, and protein content, these diets are not recommended in persons with chronic kidney disease.
Dietary Approaches Without Sufficient Evidence for Recommendations
Fish Oil Supplementation
Several predominantly small trials and meta-analyses of these trials have documented that high-dose omega-3 polyunsaturated fatty acid (commonly termed "fish oil") supplements lower BP in hypertensive individuals but not in nonhypertensive individuals. The effect of fish oil appears to be dose-dependent, with BP reductions occurring at doses of 3 gm d or more. In hypertensive individuals, average SBP and DBP reductions were 4.0 mm Hg and 2.5 mm Hg, respectively. In view of side effects and the high-dose required to lower BP, fish oil supplements cannot be routinely recommended as a means to lower BP.
Practical Considerations and Recommendations
Individual-Based Approaches: Behavioral Interventions
A large number of behavioral intervention trials have tested the effects of dietary change on BP. A variety of theories and models have informed the design of these trials (social cognitive theory, self-applied behavior modification techniques "behavioral self-management," the relapse prevention model, and the transtheoretical or stages-of-change model). Application of these models and theories often leads to a common intervention approach that emphasizes behavioral skills training, self-monitoring, and self-regulation, along with motivational interviewing.
Typically, these trials enrolled motivated individuals, who expressed readiness to change, at least at the start of the trial. Further, these studies relied on skilled interventionists, often health educators or dietitians, who met frequently with participants. Characteristic findings are successful behavior change over the short-term, typically 6 months during the height of intervention intensity, and then subsequent recidivism when intervention intensity diminishes. The limited long-term success of intensive behavioral intervention programs highlights the importance of environmental changes that facilitate adoption of desirable lifestyle changes in broad populations. Indeed, even motivated individuals find it difficult to sustain behavior change given powerful cultural forces, societal norms, and commercial interests that encourage a sedentary lifestyle, a suboptimal diet, and overconsumption of calories. Despite these impediments, available evidence from efficacy studies is sufficiently robust and persuasive to advocate dietary change as a means to lower BP and thereby prevent BP-related CVD.
Individual-Based Approaches: Clinic-Based Approaches
By example and through advice, physicians have a powerful influence on their patients' willingness to make dietary lifestyle changes. Although frequent and intensive behavioral counseling is beyond the scope of typical office practices, simple assessments (eg, measurement of body mass index) and provision of basic advice (eg, "eat less, move more") is feasible. The success of physician directed attempts to achieve lifestyle changes is dependent on several factors including the organizational structure of the office, the skills of the physician and staff, and the availability of management algorithms that incorporate locally available resources.
Physician-directed lifestyle advice should be based on the patient's willingness to make lifestyle changes.
Motivated patients should be referred to a health educator, skilled dietitian, or a behavioral change program, in large part, because success typically requires frequent contacts and visits. However, even without such programs, physicians should routinely encourage lifestyle modification.
Public Health Strategies
Ultimately, people select the types and volume of food they eat and the amount of physical activity they perform. Still, as noted by other policy-making bodies, the environment (cultural forces, societal norms, and commercial interests) has a powerful influence on whether people consume excess calories, follow a healthy diet, and are physically active. In view of the tremendous adverse impact of the environment and the vast scope of the BP epidemic, an effective public health strategy must be implemented concurrent with individual-based medical care. Government, the food industry, and employers each have a vital role. A comprehensive public health strategy must be multifactorial -- no one strategy applies to each of the known dietary factors that affect BP. For weight reduction, environmental changes include prominent calorie labeling at point of purchase in both restaurants and stores, and government initiatives that encourage rather than discourage physical activity.
Conclusions
Multiple dietary factors affect BP. Dietary modifications that lower BP are weight loss, reduced salt intake, increased potassium intake, moderation of alcohol consumption (among those who drink), and consumption of an overall healthy dietary pattern, similar to a DASH-style diet. Other aspects of diet may also affect BP, but the effects are small and or the evidence is uncertain. In view of the age-related rise in BP in both children and adults, the direct progressive relationship of BP with cardiovascular-renal diseases throughout the usual range of BP, and the worldwide epidemic of BP-related disease, efforts to reduce BP in both nonhypertensive and hypertensive individuals are warranted. Such efforts will require individuals to change behavior and society to make substantial environmental changes. The current challenge is designing and implementing effective clinical and public health interventions that lead to sustained dietary changes among individuals and more broadly in the general population.