Journal of Human Hypertension (2004) 18, 545–551 & 2004 Nature Publishing Group All rights reserved 0950-9240/04 $30.00 www.nature.com/jhh
REVIEW ARTICLE
Prevalence, awareness, treatment and control of hypertension in North America, North Africa and Asia PK Whelton, J He and P Muntner Department of Epidemiology, Tulane University School of Public Health and Tropical Medicine, Department of Medicine, Tulane University School of Medicine, New Orleans, LA, USA
Results from national surveys of prevalence, awareness, treatment and control provide the most meaningful basis for assessing the burden of hypertension in the community. National surveys conducted in a variety of countries in North America, Europe, Australia, Asia and Africa have identified a strikingly similar relationship between age and blood pressure (BP), with a progressive and steep increase in systolic BP throughout adult life and a less steep increase in diastolic BP from adolescence until the fifth or sixth decade. In most countries surveyed, there was a high prevalence of hypertension. Approximately, one quarter of all adults in the United States and Egypt had hypertension (systolic BPX140 mmHg or diastolic BPX90 mmHg or use of antihypertensive medication) in national surveys conducted in 1988–1991 and 1991–1993, respectively. The corresponding percentage was somewhat lower (14.4%)
for adults surveyed in China during 1991, but temporal trends indicate that the prevalence of hypertension is increasing rapidly in that country. In the 1988–1991 national survey, more than 25% of US adults were unaware of their diagnosis, only 55% were being treated with antihypertensive medication and only 29% were on antihypertensive medication with a systolic/diastolic BP 4140/90 mmHg. The situation was much worse in Egypt and China, with only 8% and o5% of adults with hypertension, respectively, being treated with antihypertensive medication and having a systolic/diastolic BP o140/90 mmHg. These survey results underscore the fact that hypertension is highly prevalent, poorly treated and controlled, and an escalating health challenge in economically developing countries. Journal of Human Hypertension (2004) 18, 545–551. doi:10.1038/sj.jhh.1001701
Keywords: blood pressure; epidemiology; review
Introduction Cardiovascular disease (CVD) is the most common cause of death in economically developed countries and is a rapidly evolving cause of mortality and morbidity in the industrialized nations of Eastern Europe and in economically developing countries.1 World Health Organization projections suggest that mortality from CVD is likely to continue its rapid escalation in the economically developing world, if unchecked. Based on current trends, it is projected that ischaemic heart disease will be the most important and stroke the fourth most important contributor to disability adjusted years of life lost on a worldwide basis.2 Optimal approaches to prevention of CVD are depicted in Figure 1. The most obvious and natural societal response to our epidemic of CVD is to ensure availability of care for
Correspondence: Dr PK Whelton, Office of the Senior Vice President for Health Sciences, 1440 Canal Street, Suite 2400, TW-5, New Orleans, LA, 70112-2709, USA. E-mail:
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patients with clinical manifestations of CVD such as coronary heart disease, congestive heart failure, stroke and renal insufficiency. Unfortunately, two major barriers limit the effectiveness of this approach. First, CVD often manifests as sudden death, with little opportunity for a treatment intervention. Second, it is difficult to reverse the underlying pathophysiology of CVD once it has developed. To produce a meaningful reduction in morbidity and mortality, management of patients with existing CVD must be coupled with treatment and prevention of major modifiable risk factors for CVD.3 Currently, we have only a rudimentary knowledge of the genetic underpinning of CVD and gene therapy for common forms of CVD is almost nonexistent. In contrast, several major, modifiable environmental risk factors for CVD are well established and most appear to influence the risk of both coronary heart disease, stroke, congestive heart failure and renal insufficiency. High blood pressure (BP) is among the most important of these modifiable risk factors. Epidemiologic studies have shown that high BP is a risk factor both in the early as well as late phases of the natural history of CVD.
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Figure 1 Optimal model for prevention of CVD.
Knowledge of the prevalence of high BP and the extent to which it is being detected, treated and controlled is essential to understanding the magnitude of the problem and how well it is being addressed. Results from national surveys provide the most meaningful estimates of prevalence, awareness and control of hypertension in North America, North Africa and Asia.
Methodologic considerations Important considerations in the planning, conduct, interpretation and dissemination of results for a prevalence survey are presented in Figure 2. The overall objective should be to obtain the most accurate, precise and comprehensive results in the context of the needs for the information, the resources that are available to conduct the research and practical considerations. At the outset, a sampling scheme that will allow the investigative team to address their study objectives within the confines of what is possible should be selected. Most national surveys employ a multistage sampling scheme which allows for calculation of overall and stratum-specific prevalence estimates by appropriate statistical weighting of sample results.4 A typical approach is to select a sample of regions in the first stage. This is usually followed by sampling of urban and rural areas within each region. Stratification according to socioeconomic or other factors is frequently employed. Commonly, the next stage involves sampling of dwellings within a defined geographic segment of the urban and rural areas selected in the prior stage. In the final stage, individuals who meet the age and other study inclusion criteria are sampled. Often, the final stage is a cluster sample in which all units identified in the stage are sampled with certainty. Appropriate Journal of Human Hypertension
Figure 2 Considerations in the conduct of population surveys.
care needs to be directed to detailed planning, selection of study instruments, training and certification of data collectors, and quality control. A pilot study aimed at determining the practicality and precision of the proposed study methods is highly desirable. Data analysis and dissemination of the results should occur as quickly as possible following conduct of the field work.
Prevalence of hypertension Age-specific levels of mean systolic and diastolic BP for adult men and women in six national crosssectional surveys is presented in Figure 3.5–10 A striking feature is the similarity of the pattern for the association between age and BP in each country. Without exception, there was a progressive rise in systolic BP throughout life with a difference of 20– 30 mmHg between early and late adulthood. There was a less striking rise in diastolic BP that tended to persist until the fifth decade. In later years, average diastolic BP tended to be level or to decline slightly. For both systolic and diastolic BP, the mean level was higher in men than in women in early adulthood, but the difference narrowed progressively and
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Figure 3 Mean systolic and diastolic BP, by age and sex, in the United States of America, 1976–1980,5 Canada, 1986–1990,6 Egypt 1991– 1993,7 Australia, 1980,8 Japan, 1980,9 and Italy, 1976.10
was either nonexistent or reversed by the sixth or seventh decade. These patterns result in a progressively higher prevalence of high BP with ageing. This is demonstrated graphically for four countries in Figure 4.7,9,11,12 Using currently recommended criteria for diagnosis of hypertension (average systolic BPX140 mmHg, or average diastolic BPX90 mmHg, or use of antihypertensive medication), the overall prevalence of hypertension was in the range of 20–25%.13,14 In each country, a majority of adults had hypertension by the sixth decade. The percentages depicted in Figure 4 probably underestimate the true prevalence of hypertension because they do not include those who have a prior history of hypertension but do not meet the recommended criteria for diagnosis at the time they are surveyed. In the United States, approximately 7% of the adult population fall in this category.11 Of this group, almost 60% had been told on at least two occasions by a physician or other health care provider that they had hypertension and slightly more than half of them were currently under instructions from their
health care provider to adopt a lifestyle change aimed at lowering their BP. National surveys have been conducted on a repetitive basis in both the United States and the People’s Republic of China.12,15 Temporal trends in age-specific and age-adjusted prevalence of hypertension for these two countries is presented in Figure 5. In the United States, there has been an apparent and progressive decline in age-specific and age-adjusted prevalence of hypertension. It seems unlikely that all of the decline has resulted from differences in survey techniques. Some of the change can be accounted for by improved treatment of hypertension, but there also appears to have been a progressive downward shift in the entire distribution of BP. In contrast to the experience in the United States, there has been a progressive increase in the prevalence of age-specific and age-adjusted hypertension in China. If current trends continue, the prevalence of hypertension in China will soon match or exceed that seen in the United States. This trend is probably representative of a broader tendency for a reduction in the prevalence of Journal of Human Hypertension
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Figure 4 Prevalence of hypertension (systolic BPX140 mmHg or diastolic BPX90 mmHg or treatment with antihypertensive medication) in the United States of America, 1998–1991,11 Peoples Republic of China,12 Egypt7 and Japan.9
hypertension in the most economically developed countries of the world and a progressive rise in the prevalence of hypertension in economically developing countries. Given that more than 80% of the world’s population lives in economically developing nations it is very likely that the worldwide burden of illness due to hypertension will continue to escalate unless measures are taken to blunt the expected increase in prevalence of hypertension.
Awareness, treatment and control of hypertension Temporal trends for awareness, antihypertensive drug treatment and control of hypertension in those being treated with medication in the United States is presented in Figure 6.15 There has been an impressive increase in awareness, treatment and control of hypertension using the criteria for diagnosis that were recommended during the 1960s and 1970s (systolic BP 4160 mmHg, or diastolic BP 490 mmHg, or treatment with antihypertensive medication) Application of these criteria to the most recent National Health and Nutrition Examination Survey (NHANES III) suggests almost 90% of adults with this level of hypertension were aware of their diagnosis, almost 80% were being treated with antihypertensive medication, and in nearly twothirds systolic/diastolic BP was being controlled to a level o160/95 mmHg. Despite the encouraging nature of these trends, they tend to provide a false Journal of Human Hypertension
sense of the extent to which progress has been made in reducing the societal burden of illness due to hypertension. Population attributable risk estimates indicate that a systolic BP 4160 mmHg accounts for only about 24% of the BP-related burden of illness in the community.16 Use of the currently recommended systolic/diastolic BP cut-points of 140/90 mmHg provides more meaningful criteria for recognition of hypertension. For example, population attributable risk estimates suggest that a systolic BP 4140 mmHg accounts for approximately two-thirds of the BP-related burden of illness in the community. Use of the 140/90 mmHg systolic/diastolic cutpoints indicates that there has been improvement in awareness, treatment and control of hypertension during the timeframe that this approach to diagnosis of hypertension has been recommended in the United States. However, in the most recent NHANES III survey more than one-quarter of those identified as having hypertension were unaware of their diagnosis, only slightly more than half were being treated with antihypertensive medication, and less than one-third had a systolic/diastolic BP o140/90 mmHg during pharmacotherapy. As depicted in Figure 7, awareness, treatment and control was better in women than in men. In China, less than 5% of the adults with hypertension who were identified in the 1991 national survey had their BP controlled to a level o140/90 mmHg. In Egypt, the corresponding percentage in the 1993 national survey was 8%. In both China and Egypt, awareness, treatment and control of hypertension was greater in urban areas compared to rural areas.
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Figure 5 Temporal trends in age-specific and age-adjusted prevalence of hypertension (systolic BPX140 mmHg or diastolic BPX90 mmHg or treatment with antihypertensive medication) in the United States13 and peoples Republic of China.12
Figure 6 Temporal trends for awareness, treatment and control of hypertension in the United States of America.13
Implications of survey results The prevalence, awareness, treatment and control results presented in the two preceding sections have important implications for both clinicians and public health professionals. They underscore the fact that hypertension remains highly prevalent in the United States and is becoming increasingly common in economically developing countries such as Egypt and China. Further, the results indicate that awareness, treatment and control of hypertension in the community is inadequate in both economically
developed and economically developing countries. The situation in economically developing countries deserves special attention. In this setting, prevalence of hypertension appears to be rising rapidly and the societal response is fragmented with very low levels of awareness, treatment and control. In this context, a national strategy that aims for enhanced public and health professional awareness, screening linked to treatment opportunities and increased access to affordable medications may be specially important. In the United States and other economically developed countries, improving the Journal of Human Hypertension
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Figure 7 Percent of adults with hypertension (systolic BPX140 mmHg or diastolic BPX90 mmHg or treatment with antihypertensive medication) in the United States of America,11 the Peoples Republic of China,12 and Egypt7 who were aware of their diagnosis, being treated with antihypertensive medication, and recorded as having an average systolic/diastolic BP o140/90 mmHg while being treated with antihypertensive medication.
processes for incorporating recommended hypertension treatment strategies in health care delivery systems, targeting lower BP goals in persons at higher risk for CVD, greater attention to nondrug approaches for treatment of hypertension, and enhancing adherence to drug and nondrug therapy of hypertension may be of particular relevance. In both settings, treatment strategies should be coupled with attempts to prevent the development of hypertension.17,18 Despite the challenges associated with design and implementation of meaningful attempts to prevent and treat hypertension on a national basis, the potential for health benefits that accrue from a successful strategy make continued efforts in this direction an important health priority. Health professionals have a particularly important responsibility for education of their peers, policy makers and the general public and for facilitating the creation of adequately funded national hypertension prevention, detection and treatment programs.
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