skip page navigationOregon State University

Research Newsletter-Spring/Summer 2009


Victoria J. Drake, Ph.D.
LPI Research Associate

The term blood pressure refers to the force of blood exerted against the walls of blood vessels, especially the arteries, as the heart pumps blood to the rest of the body. Blood pressure is expressed in units called "millimeters of mercury" (mm Hg). There are two measurements of arterial pressure: systolic blood pressure and diastolic blood pressure. Systolic blood pressure (SBP), the higher of the two numbers, is the maximum arterial pressure when the heart contracts or beats. Diastolic blood pressure (DBP) is the minimum arterial pressure when the heart relaxes between heartbeats. Blood pressure readings are expressed as systolic pressure over diastolic pressure. For example, a blood pressure measurement of 120/80 mm Hg means that systolic blood pressure is 120 mm Hg and diastolic pressure is 80 mm Hg.

Blood pressure naturally fluctuates throughout the day according to a number of factors, including body temperature, diet, physical activity, emotional state, and use of certain drugs or medications. Normal blood pressure is currently defined as a SBP lower than 120 mm Hg and a DBP lower than 80 mm Hg. Hypotension refers to abnormally low blood pressure, most often defined as a SBP lower than 90 mm Hg or a DBP lower than 60 mm Hg. More of a public health concern, however, is abnormally high blood pressure, called hypertension. Hypertension is defined as a SBP of 140 mm Hg or greater or a DBP of 90 mm Hg or greater (see table below). Prehypertension, defined as a SBP of 120-139 mm Hg or a DBP of 80-89 mm Hg, is not clinical hypertension, but blood pressure readings are elevated above optimal levels. The causes of elevated blood pressure are multifactorial, with genetic and environmental influences. The majority of patients with high blood pressure have decreased elasticity and increased peripheral resistance in blood vessels. Both prehypertensive and hypertensive individuals are at a heightened risk for coronary heart disease, stroke, and kidney disease. "White-coat hypertension" is a condition in which a patient displays elevated blood pressure only in a clinical setting, such as a doctor’s office, and is probably caused by anxiety.

Categories of SBP and DBP for Adults

Almost one-third of U.S. adults—72 million Americans—have hypertension, and according to current estimates, nearly as many have prehypertension. Many people do not realize that they have high blood pressure because the disease itself does not usually cause symptoms. Symptoms often manifest only after organ damage, which results from long-term elevation of blood pressure. Thus, blood pressure should be monitored at regular intervals, and high blood pressure should be managed. Although there are a number of pharmaceuticals used to treat high blood pressure, prehypertension and hypertension can often be managed through diet and lifestyle modification, possibly preventing or delaying the need for medication. Such strategies include dietary changes, regular aerobic exercise, smoking cessation, and stress reduction.

A number of dietary changes can help lower blood pressure in people with normal or high blood pressure. High sodium intakes are linked with high blood pressure. Accordingly, several randomized controlled trials have found that dietary sodium or salt reduction lowers blood pressure. One analysis found that modest sodium reduction (1,800 mg/day of sodium or 4.6 grams/day of salt) in individuals with elevated blood pressure lowered SBP by 5 mm Hg and DBP by 2.7 mm Hg. A low sodium diet was also found to reduce SBP by 2 mm Hg and DBP by 1 mm Hg in subjects with normal blood pressure. On average, Americans consume 4,000 mg of sodium (10 grams of salt) daily. Of this amount, about 75% is derived from processed food; only about 5% is discretionary salt use—salt added at the table. Eliminating processed foods with their added salt from the diet dramatically lowers sodium intake and helps control blood pressure. According to USDA recommendations, healthy adults should limit sodium consumption to 2,300 mg daily (5.8 grams of salt), which is about a teaspoon of salt. Individuals who tend to be more sensitive to the effects of sodium on blood pressure—those with diagnosed hypertension, people over 50 years of age, and individuals of African descent—should consume less than 1,500 mg of sodium (3.8 grams of salt) daily.

Compared to a typical American diet, the DASH (Dietary Approaches to Stop Hypertension) eating plan has been shown to significantly lower blood pressure in individuals with hypertension, as well as in those with normal blood pressure. The DASH diet emphasizes fruits, vegetables, whole grains, poultry, fish, nuts, and low-fat dairy products, and compared to the usual American diet, it is markedly higher in potassium and calcium, modestly higher in protein, and lower in total fat, saturated fat, and cholesterol. In the initial DASH trial, sodium levels were kept constant throughout the study in order to better evaluate the effects of other dietary components. The more recent DASH-sodium trial compared the DASH diet with a typical American diet at three levels of salt intake: low (2.9 grams/day), medium (5.8 grams/day, recommended by U.S. dietary guidelines), and high (8.7 grams/day, typical U.S. intake). At each level of salt intake, individuals on the DASH diet had lower SBP and DBP compared to individuals on the typical American diet. This blood pressure reduction was observed in individuals with hypertension and in those with normal blood pressure. The combination of the DASH diet and reduction in salt had an additive effect, lowering blood pressure more than either intervention alone.

Several other dietary factors may affect blood pressure. For instance, consuming excessive amounts of alcohol is associated with hypertension. In fact, drinking more than two alcoholic drinks daily dose-dependently increases blood pressure. Accordingly, heavy drinkers who decrease their consumption of alcoholic beverages experience a dose-dependent reduction in both SBP and DBP. Moderate amounts of alcohol—two drinks daily for men and one drink daily for women—may not significantly increase blood pressure and, compared to nondrinkers, may actually decrease blood pressure in women. Moreover, moderate consumption of alcohol has been associated with significant reductions in the risk of coronary heart disease, ischemic stroke, and overall mortality. However, drinking more than this amount increases the risk for hypertension, various cancers, and mortality. Thus, limiting alcohol consumption is important for controlling blood pressure. Consumption of caffeine may also affect blood pressure. While caffeine consumption is known to acutely increase blood pressure, considerably less is known regarding the effect of habitual caffeine consumption on blood pressure. Randomized controlled trials examining caffeine or coffee intake on blood pressure have reported conflicting results. One pooled analysis of such trials reported that regular caffeine consumption (as tablets) was associated with a 4.2 mm Hg increase in SBP and a 2.4 mm Hg increase in DBP. However, the blood pressure-raising effect of caffeine was blunted when the caffeine was ingested as coffee, presumably because other compounds in coffee counteract caffeine's effect on blood pressure. Also, several observational studies have found that vitamin C intake or plasma level of vitamin C is inversely associated with blood pressure. Results of intervention trials examining the effect of vitamin C supplementation on blood pressure have been mixed, but most trials have reported beneficial effects with daily doses of 500-1,000 mg. Large-scale, long-term studies are needed to determine whether supplemental vitamin C is effective in preventing or treating hypertension. Additionally, some studies indicate that regular consumption of flavonoid-rich foods, such as wine, tea, and cocoa, may reduce blood pressure. Flavonoids and vitamin C may improve nitric oxide-induced vasodilation, which relaxes or opens blood vessels.

In addition to dietary changes, regular aerobic exercise has been shown to lower resting blood pressure in people with normal or high blood pressure. One pooled analysis of controlled trials found that aerobic exercise significantly reduced blood pressure by an average of 3.8 mm Hg for SBP and 2.6 mm Hg for DBP. The blood pressure-lowering effect observed in this analysis was not dependent on weight loss of participants or on the frequency, intensity, or type of aerobic exercise. Another pooled analysis reported that progressive resistance exercise decreased both resting SBP and DBP by 3 mm Hg. It is not clear how regular aerobic or resistance exercise lowers blood pressure, but suggested mechanisms include decreased peripheral resistance in blood vessels, effects on the nervous and renal systems, and reductions in body weight. Blood pressure reductions resulting from routine physical activity may be more pronounced in overweight or obese individuals compared to those who are normal weight. Individuals should aim for at least 30 minutes of moderate-intensity physical activity, such as brisk walking, most days of the week. Regular exercise is important in the prevention and treatment of hypertension and offers other health benefits as well.

picture measuring blood pressure

Regular exercise is a key component in weight loss and weight maintenance programs. Weight loss will significantly lower blood pressure in overweight or obese individuals; even a 10-lb (4.5-kg) weight reduction can help control blood pressure. Individuals should aim for a healthy weight with a body mass index (BMI) of 18.5-24.9 kg/m2. BMI is calculated by dividing weight in kilograms by height in meters squared. Overweight is defined as a BMI of 25.0- 29.9 kg/m2, and obesity is defined as a BMI of 30 kg/m2 or higher. In addition to having a higher BMI, greater amounts of abdominal fat (waist circumference > 40 inches for men and > 35 inches for women) increase the risk for hypertension. According to the National Heart, Lung, and Blood Institute, overweight and obese individuals should strive for a 10% loss in body weight over a six-month period. Weight loss of 22 lbs (10 kg) generally results in 5-20 mm Hg reductions in SBP.

Smoking cessation and stress relief may also lower blood pressure. It is wellestablished that cigarette smoking increases the risk of heart disease and stroke in individuals with hypertension. Cigarette smoking causes injury to the vascular endothelium—the single cell layer that lines the inner surface of blood vessels. Thus, cessation of cigarette smoking would decrease one’s risk for cardiovascular diseases, in addition to other chronic diseases. Further, stress relief techniques like meditation may help manage blood pressure, although scientific studies are largely lacking.

The interventions discussed above—dietary sodium reduction, adherence to the DASH diet, moderating alcohol consumption, regular exercise, weight loss, and smoking cessation—can help control blood pressure and reduce the risk for cardiovascular diseases. Such modifications may be sufficient to prevent or treat hypertension or may improve antihypertensive drug efficacy in individuals who require medication. These dietary and lifestyle strategies should be discussed with a competent medical professional, who can help personalize a plan to help prevent or treat high blood pressure. Controlling blood pressure will lower the risk of heart disease, stroke, and kidney disease, as well as decrease risk of overall mortality. Thus, reducing blood pressure through changes in diet and lifestyle would result in significant public health benefits.

Useful Web sites:

Dietary sodium and blood pressure
National Health, Lung, and Blood Institute
American Heart Association journal article in Hypertension

DASH diet
National Health, Lung, and Blood Institute

Weight loss
National Health, Lung, and Blood Institute

Centers for Disease Control and Prevention

Smoking cessation
Centers for Disease Control and Prevention

Last updated June 2009