Can exercise and proper nutrition protect clients from this “silent killer”?
Hypertension is a widespread health problem that affects nearly 25% of the adult population in the United States (Fang, Wylie-Rosett & Alderman 2005). Hypertension increases the risk of cardiovascular disease—the number-one cause of death in the U.S.—and other maladies, including renal disease, stroke, heart failure and peripheral artery disease. Although hypertension is defined as systolic blood pressure (SBP) > 140 millimeters of mercury (mm Hg) and/or diastolic blood pressure (DBP) > 90 mm Hg, risk factors can be seen when blood pressure is as low as 115/75 (SBP/DBP) and begin to double in risk for every 20/10 increase (Pescatello et al. 2004a). A new classification, “prehypertension” (SBP = 120–139 and DBP = 80–89), has been introduced to identify individuals who are at a higher risk of developing the condition.
The benefits of exercise in combating hypertension have been promoted by a number of health organizations and individuals, including the American Heart Association, the American College of Sports Medicine (ACSM), the National Institutes of Health, the Centers for Disease Control and Prevention, and the Surgeon General of the United States (Wallace 2003). Although hypertension studies are ongoing, ample research provides clear evidence of the positive effects of exercise. This research update will discuss the role of intensity, duration and modality; the combined effects of exercise, diet and weight loss; the value of exercise as a preventive measure; and the possible underlying physiological mechanisms relating to exercise’s antihypertensive benefits.
Most exercise recommendations for hypertensive patients suggest a duration of 20–60 minutes of low- to moderate- intensity cardiovascular exercise (40%– 70% VO2max) performed three to five times a week (Wallace 2003). The results of several studies confirm that low- to moderate-intensity training is just as efficient in lowering BP as high-intensity training (>70% VO2max) (Halbert et al. 1997). An individual’s fitness level may play a central role in determining optimal intensity. A recent study of 49 middle-aged men with normal-high (SBP = 130–139; DBP = 85–89) to stage 1 hypertension (SBP = 140–159; DBP = 90–99) randomly assigned to a light or moderate (40% or 60% VO2max) exercise protocol found that lower-intensity exercise led to more reductions in BP in the older, less fit subjects, whereas moderate-intensity exercise was more effective in the physically fit men (Pescatello et al. 2004b).
Although more research is needed to better specify the optimal intensity, the general guidelines of moderate-intensity exercise for 30 minutes or more on most days of the week are appropriate for successfully lowering elevated BP levels. The good news is that moderate-intensity exercise programs can be readily implemented and are easily maintained for many populations. In addition, they impart less musculoskeletal injury for previously sedentary populations, who are not accustomed to vigorous physical exertion.
Cardiovascular Training. A significant amount of evidence indicates that cardiovascular training helps reduce BP. In a meta-analysis of 54 clinical trials, findings included a reduction in SBP of an average of 3.84 and in DBP of an average of 2.58 in hypertensive men and women (Whelton et al. 2002).
Resistance Training. Although to date there is less research on the effect of resistance exercise on BP, one recent meta-analysis found a decrease of 3.2 and 3.5 for SBP and DBP, respectively (Cornelissen & Fagard 2005a). Yet there is debate—in fact, an association has been shown between vigorous resistance training and reduced arterial compliance (i.e., the arteries stiffen and do not expand as well to increased blood flow) (Miyachi et al. 2003), which can lead to an increase in SBP. However, a study by Kawano and colleagues (2006) demonstrated that aerobic training performed in conjunction with resistance training negated the decrease in arterial compliance. This suggests that resistance training should be accompanied by aerobic training as an intervention strategy, which is in agreement with the ACSM recommendations for the prevention, treatment and control of hypertension (Pescatello et al. 2004a).
Alternative Exercise Modes. A recent Chinese study found that qigong (a series of relaxation, breathing, gentle movement and walking exercises) resulted in the reduction of both SBP and DBP (Cheung et al. 2005). This notable finding may lead to further research into alternative exercise methods that may be beneficial in reducing BP.
Overweight and obesity are associated with many cardiovascular risks, including hypertension. Exercise has become a staple in weight management and weight loss programs, but is mostly effective when implemented concurrently with diet modifications. Specific dietary guidelines that have been shown to lower hypertension are explained in the Dietary Approaches to Stop Hypertension (DASH) diet, which recommends a diet rich in fruits, vegetables and low-fat dairy foods, as well as restrictions in alcohol and sodium intake (Bacon et al. 2004). A recent review of lifestyle interventions found that combining these recommendations with the intake of fish oil supplements resulted in significant reductions in BP (Dickinson et al. 2006). Although other studies have suggested that potassium, magnesium and calcium supplementation also play a role in BP reduction, the Dickinson review failed to find strong clinical support for these claims.
Controversy remains over whether combining exercise with weight reduction has an “additive” effect. Both have been shown to help reduce BP independently, yet a comprehensive review by Hagberg and colleagues (2000) concluded that exercise training and dietary weight loss are independent, and that exercise can be effective in lowering BP without concomitant reductions in body weight. Other reviews maintain this idea but also recommend combining diet and exercise to facilitate weight loss (Bacon et al. 2004).
Regular exercise should be encouraged not only as a treatment method for individuals with hypertension but also as a means of prevention. Predictors that may be examined to evaluate the risk of developing hypertension include resting BP, family history and physical activity levels. Research has demonstrated that higher physical activity levels and the development of hypertension have an inverse relationship. For example, Barengo and associates (2005) presented evidence that European men doing > 4 hours per week of leisure-time physical activities (e.g., recreational sports, skiing, gymnastics, heavy gardening, hunting, fishing and walking/jogging) had a reduced risk of hypertension.
The acute responses to exercise are the physiological changes that occur within only a few exercise sessions; the chronic adaptations are derived from the accumulation of continual exercise bouts over a period of time.
The underlying mechanisms relating to the antihypertensive benefits of exercise are not completely understood; however, several studies have shown connections to specific physiological mechanisms. An immediate (acute) reduction in BP following exercise has been termed postexercise hypotension, and researchers agree that it is caused by reductions in vascular resistance (the resistance to flow that must be overcome to push blood through the circulatory system) (Hamer 2006). The mechanisms associated with the chronic adaptations to blood pressure are more complex. A recent meta-analysis suggests that these adaptations can be partially explained by a decreased systemic vascular resistance in which the autonomic nervous system and renin- angiotensin system (a hormone system that helps normalize long-term BP and blood volume in the body) are most likely the underlying regulatory mechanisms (Cornelissen & Fagard 2005b). In addition, regular cardiovascular exercise leads to an increase in nitric oxide production from different sites in the body, which causes vasodilation (an increase in the internal diameter of a blood vessel that results from relaxation of smooth muscle within the vessel wall).
Since hypertension is associated with an increased risk of cardiovascular disease, effective interventions are vital to reduce overall morbidity and mortality. Although pharmacological treatments can be necessary for treating some BP conditions, lifestyle modifications should also be implemented whenever possible. Research has demonstrated that exercise can be consequential in lowering SBP and DBP. Both cardiovascular training and resistance training facilitate antihypertensive responses, although cardiovascular exercise has been more widely studied. Specifics concerning optimal intensity and duration are yet to be fully determined; for now, moderate-intensity exercise performed for at least 30 minutes on most days of the week is recommended as the “minimal,” yet effective, formula for promotion of overall health.