Section Five: Foods and Blood Pressure

Hypertension is among the most common problems that will confront your patients. One in every four American adults has, or is being treated for, high blood pressure, defined as a systolic pressure of 140 mm Hg or greater and/or a diastolic pressure of 90 mm Hg or greater. In 1992, medical treatment of hypertension cost $12.5 billion. The personal and social costs are many times higher.

The condition takes a disproportionate toll among African Americans. Among men, the age-adjusted prevalence is 34 percent for African Americans, compared to 25 percent for whites. For women, hypertension affects 31 percent of African Americans, compared to 21 percent of whites.¹

High blood pressure is dangerous. It increases the risk of heart disease, stroke, and other serious problems. While pharmacologic treatment is often necessary for controlling blood pressure, diet plays a central role, both in its cause and treatment.

Reducing Sodium

Dietary sodium is a well-known contributor to high blood pressure. Sodium holds water, and the increased water content in the vascular system increases blood pressure. The effect of reducing salt intake is often modest, but is nonetheless important.

Patients often have little idea as to which foods contribute sodium to their diet. Aside from table salt, the highest-sodium foods by far are frozen meals and canned and snack products, due to the addition of salt during processing. Dairy products are the next highest in sodium, followed by meats. In their natural state, plant foods—grains, legumes, vegetables, and fruits—have almost no sodium. Patients should be encouraged to favor fresh or frozen vegetables and beans, rather than canned products, and reduced sodium products are also increasingly available.

Vegetarian diets are best known for their use in the reversal of atherosclerotic lesions in the coronary arteries. However, such diets are also invaluable for treating hypertension.

Vegetarians have a much lower prevalence of hypertension compared to meat-eaters. The research establishing the differential effects of meat-based and vegetarian diets began with comparisons of religious groups following different dietary customs. For example, both Mormons and Seventh-day Adventist avoid coffee, alcohol, tea, and tobacco, but most Mormons are omnivores, while about half of all Adventists are vegetarians. Vegetarian Adventists were found to have systolic pressures that were eight to nine points lower and diastolic pressures that were six to eight points lower, compared with Mormon omnivores.²

A study of Caucasian Adventists found hypertension in 22 percent of omnivores, but only 7 percent of vegetarians. Among African Americans, the prevalence was 44 percent for omnivores and 18 percent of vegetarians.³

Used clinically, a vegetarian diet reduces both systolic and diastolic blood pressure by as much as 10 percent, an effect that is independent of salt intake.^4,5

The mechanism by which the diet change works is not clear. A vegetarian diet promotes weight loss, but the drop in blood pressure occurs before any substantial weight change. More likely, the change in blood pressure is due to the lower blood viscosity that follows a reduction in dietary fat.^6,7 The vitamin C and omega-3 fatty acid content of vegetarian diets may also contribute to blood pressure lowering.⁸

For tips on helping patients to make a transition to a vegetarian diet, see Section 1 on reversing heart disease.

Foods and Blood Pressure Study Questions

1. What kinds of diets are associated with high blood pressure?
2. What foods would you recommend your patients avoid? What are the alternatives?

References
1. Burt VL, Cutler JA, Higgins M, et al. Trends in the prevalence, awareness, treatment, and control of hypertension in the adult US population. Data from the health examination surveys, 1960 to 1991. Hypertension 1995;26:60-9.
2. Rouse IL, Armstrong BK, Beilin LJ. Vegetarian diet, lifestyle and blood pressure in two religious populations. Clin Exp Pharmacol and Physiol 1982;9:327-30.
3. Melby CL, Goldflies DG, Hyner GC, Lyle RM. Relation between vegetarian/nonvegetarian diets and blood pressure in black and white adults. Am J Publ Health 1989;79:1283-8.
4. Rouse IL, Beilin LJ. Editorial review: vegetarian diet and blood pressure. J Hypertension 1984;2:231-40.
5. Anderson JW. Plant fiber and blood pressure. Ann Intern Med 1983;98(Part 2):842.
6. Ernst E, Pietsch L, Matrai A, Eisenberg J. Blood rheology in vegetarians. Br J Nutr 1986;56:555-60.
7. Ernst E, Matrai A, Pietsch L. Vegetarian diet in mild hypertension. Br Med J 1987;294:180.
8. Berry EM, Hirsch J. Does dietary linolenic acid influence blood pressure? Am J Clin Nutr 1986;44:336-40.