Hypertension in aging: physical activity as primary prevention

Abstract

In most physiologic systems, there is considerable evidence that the normal aging processes do not result in significant impairment or dysfunction in the absence of pathology and under resting conditions. However, in response to a stress, the age-related reduction in physiologic reserves causes a loss of regulatory or homeostatic balance. This happens before an individual notices that something is wrong. An additional consequence of age-related changes is an increased perception of effort associated with submaximal work. Thus, a vicious cycle is set up, leading to decreasing exercise capacity, resulting in an elevated perception of effort, subsequently causing avoidance of activity, and finally feeding back to exacerbation of the age-related declines secondary to disuse. Sedentary behavior is an important risk factor for chronic disease morbidity and mortality in aging. However, there is a limited amount of information on the type and amount of activity needed to promote optimal health and function in older people [19]. The purpose of this review is to discuss the important role of exercise training as a primary prevention tool to hypertension. In addition, this review will address the topic of the recommended amount of physical activity required for health promotion along with the current exercise guidelines.

Exercise training and blood pressure

By the year 2030, the number of individuals 65 years and over will reach 70 million in the USA alone; persons 85 years and older will be the fastest growing segment of the population. As more individuals live longer, it is imperative to determine the extent and mechanisms by which exercise and physical activity can improve health, functional capacity, quality of life, and independence in this population. Aging is a complex process involving many variables (e.g., genetics, lifestyle factors, chronic diseases) that interact with one another, significantly influencing the manner in which we age [1].

Many studies provide evidence that in developed nations such as the USA, a sedentary lifestyle contributes significantly to development of the major risk factors for age-related disease, prominent among them being obesity, diabetes, and hypertension [44]. Conversely, there is increasing evidence that a high level of activity during old age and consequently an influence on the aging process can be achieved by regular training initiated as early as young adulthood. The focus of this training process should be on improving muscle strength, general flexibility, and cardiovascular exercise. Thus, it is appropriate to perceive physical activity as a medical prescription for the aging population [4, 34].

The high prevalence of hypertension in modern industrialized societies imposes a considerable public health problem [35], and therefore, prevention of hypertension is a major public health objective. Hypertension is a serious health problem that increases the risk of coronary heart disease, stroke, and kidney disease [29, 41]. Physical inactivity has been shown to be associated with hypertension in epidemiologic studies [5, 37]; hence, physical activity has been recommended in the prevention and treatment of hypertension [21, 28, 30].

A large body of data demonstrates that changes toward a more physically active lifestyle positively affect blood pressure response in normotensive and hypertensive individuals [8, 22, 39]. A meta-analysis of longitudinal aerobic training studies [24], in mild essential hypertensive subjects, demonstrates an average reduction in resting systolic and diastolic blood pressures of 10.8 and 8.2 mmHg, respectively [22]. Therefore, participation in an exercise training program can be viewed as a nonpharmacological approach for preventing and treating mild hypertension.

High physical fitness is associated with lower blood pressure in both men and women [8, 16, 20]. Data indicate an association between baseline physical activity fitness and risk of future hypertension. Multiple regression evaluation demonstrated that untrained individual had a 62% increased risk of developing hypertension compared to their trained peers [6]. Furthermore, this study demonstrates that changing sedentary lifestyle habits to a more active lifestyle is coupled with a reduced risk of becoming hypertensive. Moreover, in a follow-up test the incidence of hypertension in the group who stayed untrained was 32 per 1,000, as compared to only 18 per 1,000 in those who improved their fitness category. Hence, enhanced levels of physical fitness play a significant primary prevention for hypertension [16, 20].

The effects of fitness on mortality among hypertensive adults, either from cardiovascular disease or from all causes, are not fully understood, especially among women [20]. The objective of this study was to examine the effect of fitness on all-cause and cardiovascular disease mortality among hypertensive and normotensive women and men. Using the Lipids Research Clinics Prevalence Study, the relationship of fitness with mortality among 2,712 women and 3,000 men followed from 1972–1976 to 1998 were examined. Cardiorespiratory fitness was measured using a treadmill test. Sex-specific hazards were calculated from proportional hazard models of fitness predicting all-cause or cardiovascular disease mortality, adjusted for age, education, race, smoking, alcohol, body mass index, and hyperlipidemic sampling strata. Comparing the lowest with the highest quintile of fitness, the adjusted all-cause mortality among hypertensive women was 1.7 (95% confidence interval = 0.9–3.2) and among normotensive women was 2.3 (1.5–3.7). Comparing the same quintiles of fitness, the adjusted all-cause mortality among hypertensive men was 2.0 (1.2–3.4), and among normotensive men, it was 1.9 (1.3–2.7). Elevated risks were also observed for cardiovascular disease mortality. The authors of this study concluded that higher levels of fitness are associated with a lower risk of all-cause and cardiovascular disease mortality among both hypertensive and normotensive women and men. The relative beneficial impact of physical fitness on blood pressure and all-cause mortality were demonstrated in normotensive and borderline hypertension subjects [7].

Regular practice of exercises, a low-calorie diet, and reduction in sodium intake are well-established nonpharmacological approaches in the nonpharmacological treatment of high blood pressure [36] and are proposed as the first strategy in the treatment of mild or moderate hypertension [15].

Previous studies have shown that a supervised exercise program leads to a decrease in blood pressure in humans with essential arterial hypertension [23, 42]. Men in the high fitness group with resting systolic blood pressure above or equal to 140 mmHg had a lower death rate than men in the low fitness group with resting systolic pressure below 140 mmHg. Nevertheless, although the reduction in blood pressure as a result of exercise training is detected in both normal and hypertensive patients, the magnitude of reduction in systolic and diastolic blood pressure at rest and during submaximal exercise is greater in hypertensive subjects [7, 14].

Recently, it was suggested that a nonsupervised exercise program followed remotely via the Internet causes a reduction in systolic and diastolic pressures—similar to those observed in supervised physical training programs [36]. That is, the nonsupervised program decreases blood pressure mainly among individuals with higher blood pressure levels. The decrease in blood pressure after a 6-month aerobic physical training program is even more extensive than after a 3-month program. This alteration in blood pressure is independent of body mass index, waist circumference, and body weight loss. Previous studies of supervised exercise programs also show that the reduction in blood pressure may be independent of body weight reduction [9, 14].

Evidences accumulated in the past few years show that nonpharmacological management should be the initial strategy to treat overweight individuals with mild to moderate hypertension [2, 46]. A single exercise session is known to decrease blood pressure in hypertensive individuals [10]. This hypotensive effect may continue with the repetition of exercise sessions over time [3, 47]. However, these beneficial effects of exercises are restricted to supervised physical training programs or cardiovascular rehabilitation programs in patients already affected by cardiac events [12, 32]. Therefore, little is known on the impact of a nonsupervised physical training program on blood pressure.

Aerobic training is not the only form of exercise found to decrease resting blood pressure. Strength training, in the form of circuit weight training, seems to produce the same effect on blood pressure as endurance training. Chronic participation in resistive exercise was once thought to produce elevated resting arterial pressure by causing vascular hypertrophy and increased vascular resistance because of large increases in arterial pressure elicited by the isometric or resistive exercise. However, studies have shown that this is not the case. Reductions in arterial pressure have been reported after isometric or resistive exercise training such as isometric handgrip exercise or weightlifting [25, 27, 33, 48].

Furthermore, epidemiological data indicate that regular exposure to high isometric activity at the workplace lowers the incidence of hypertension by as much as 29% [13]. These limited findings suggest that isometric exercise training may become an important part of a nonpharmacological intervention to prevent and combat hypertension. However, only few studies have examined the effectiveness of purely isometric training on reducing arterial pressure [25, 26] Howden et al. [26] documented a reduction of 4.7% in resting diastolic pressure after 9 weeks of a circuit resistance training program. Likewise, Stewart [44] demonstrated a reduction in mean resting blood pressure from 145/97 at baseline to 131/84 in mild hypertensive patients participating in the circuit weight training group after 10 weeks of training. The magnitude of the reduction is equal to the values observed in the walking/jogging training group.

These studies show that isometric training elicits reductions in mean diastolic and mean arterial blood pressure at rest. Although the reported reduction in diastolic arterial blood pressure appears modest (2–5 mmHg), recent studies indicate that small reductions in diastolic arterial pressure in the population could have significant health benefits. A 2-mmHg drop in diastolic arterial pressure can lead to a 17% decrease in hypertension as well as a 6% reduction in coronary heart disease and a 15% reduction in stroke-related events [17]. A 5- to 6-mmHg reduction in diastolic arterial pressure decreased coronary heart disease and stroke incidents by 16 and 38%, respectively [17]. Thus, the 5-mmHg reduction reported in this study can significantly affect cardiovascular-related illnesses. Furthermore, these results support the concept that isometric training is an effective modality in the prevention of hypertension.

Brandon et al. [11] reported the effects of a 4-month strength training program on strength and blood pressure in older adults. The training protocol for the 43 experimental subjects (age = 72.1 ± 5.5 years; weight = 72.4 ± 12.3 kg; body mass index = 26.3 ± 3.4) consisted of 8–12 repetitions at each of 50, 60, and 70% of their one repetition maximum, 3 days a week, for 16 weeks. The results revealed that systolic blood pressure remained unchanged, while mean arterial blood pressure and diastolic blood pressure decreased 2.4 and 3 mmHg, respectively. Strength and blood pressure are significantly but moderately related both before and after the training intervention. These results show that moderate intensity strength training greatly improved strength in older adults and had no adverse affect on blood pressure responses.

How does physical activity produce the decrease in blood pressure in elderly and in borderline hypertensive patients? The mechanism(s) responsible for the reduction in arterial pressure has not been investigated. One possible mechanism that may lower arterial pressure as a result of exercise training is a reduction in sympathetic nerve activity. What mechanism could be responsible for the reduction in arterial pressure observed with isometric forearm training? In Ray and Carrasco’s study [41], the lack of change in the muscle sympathetic nerve activity after training indicates that the lower arterial pressure is unrelated to a reduction in central sympathetic outflow. The failure of muscle sympathetic nerve activity to change at rest with isometric training is also typically observed with either forearm or leg dynamic exercise training [40, 43].Therefore, reductions in sympathetic outflow to the skeletal muscle do not appear to be a prerequisite to lower arterial pressure in humans. However, it cannot be excluded that sympathetic outflow to other vascular beds (e.g., visceral regions) may be reduced and may contribute to the reduction in arterial pressure at rest [41].

Another possible mechanism for the reduction in arterial pressure is peripheral vascular adaptations. Because isometric exercise elicits marked increases in muscle sympathetic nerve activity and norepinephrine release, vascular sensitivity to norepinephrine may be decreased with isometric training [31]. Isometric exercise may improve endothelial function. The increased exposure to shear stress on the vessels throughout the entire body by the pressor response during isometric exercise may upregulate the production of nitric oxide synthase and increase the release of endothelium-derived nitric oxide [18, 33, 45]. This is a potentially important effect because essential hypertension is associated with an impairment of endothelium-derived vasodilation related to nitric oxide production [38].

Conclusions

There is encouraging evidence that moderate levels of physical activity may provide protection from certain chronic diseases. Additionally, substantial health effects can be accrued independent of the fitness effects achieved through sustained vigorous activity. Thus, regular participation (i.e., 30 min/day on most days of the week) in activities of moderate intensity (such as walking, climbing stairs, biking, or yard work/gardening), which increase accumulated daily energy expenditure and maintain muscular strength, should be encouraged in older adults, even if it is of insufficient intensity for improving fitness. Participation in regular physical activity (both aerobic and strength exercises) elicits a favorable blood pressure response that contribute to healthy aging. Much has been learned recently regarding the adaptability of various biological systems, as well as the ways that regular exercise can influence them. Participation in a regular exercise program is an effective intervention/ modality to reduce/prevent a number of functional declines associated with aging. Furthermore, the trainability of older individuals is evidenced by their ability to adapt and respond to both endurance and strength training. Endurance training can help maintain and improve various aspects of cardiovascular function (as measured by maximal VO₂, cardiac output, and arteriovenous O₂ difference), as well as enhance submaximal performance. Importantly, reductions in risk factors associated with disease states (hypertension, heart disease, diabetes, etc.) improve health status and contribute to an increase in life expectancy. It is important to note that while participation in physical activity may not always elicit increases in the traditional markers of physiological performance and fitness (e.g., VO₂max, mitochondrial oxidative capacity, body composition) in older adults, it does improve health (reduction in disease risk factors) and functional capacity. Thus, the benefits associated with regular exercise and physical activity contribute to a more healthy, independent lifestyle, greatly improving the functional capacity and quality of life in this population.

Diastolic arterial pressure appears to be effectively lowered by isometric and resistive training in a large segment of the population. In summary, aerobic and isometric training are effective in lowering arterial pressure in aged normotensive subjects. Isometric training may be an effective nonpharmacological intervention in the prevention and treatment of hypertension. The reduction in arterial pressure is related to changes in muscle sympathetic nerve activity in addition to peripheral vascular adaptations. Notable aspects of aerobic and isometric forearm exercise are that it can be performed quickly, easily, and in any location. These attributes may increase elderly compliance to prescribed training interventions and thereby enhance the probability of positive clinical outcomes.