Reducing the Global Burden of Cardiovascular Disease: The Role of Risk Factors

James W. Levenson, MD, MPH, Patrick J. Skerrett, MS, J. Michael Gaziano, MD, MPH

Disclosures

Prev Cardiol. 2002;5(4) 

In This Article

The Epidemiologic Transition

Most pre-industrial societies are characterized by high rates of infant mortality, deaths primarily due to infection or malnutrition, and relatively short average life expectancy. As societies develop, infant mortality generally declines, the causes of death shift, and average life expectancy increases. This evolution is known as the epidemiologic transition. An excellent model of this transition developed by Omran[3] divides it into three basic ages -- the age of pestilence and famine, the age of receding pandemics, and the age of degenerative and man-made diseases ( Table I ). Olshansky and Ault[4] added a fourth stage, the age of delayed degenerative diseases. During the transition from one age to another, both the character and total rates of CVD change.[5]

While any specific country or region enters these ages at different times, the progression from one to another usually proceeds in a predictable manner that is closely linked with several parallel transformations. These include economic, demographic, and social changes that pave the way for major shifts in a population's health. The economic transition is characterized by increasing per capita income; the social transition by industrialization and the resulting urbanization, the development of a public health infrastructure, wider access to health care, and increasing application of health technologies; and the demographic transition by declining fertility and age-adjusted mortality rates, leading to increases in life expectancy and an aging population.

Humans evolved under conditions of pestilence and famine and have lived with them for most of recorded history. Deaths due to malnutrition and infectious disease characterize this age, and the high rates of infant and child mortality result in a low mean life expectancy. Many countries that have become today's established market economies began to emerge from the age of pestilence and famine during the 18th and 19th centuries. The transition through this earliest stage is occurring much later -- but more rapidly -- in the emerging market economies and the developing economies, driven largely by the transfer of low-cost agricultural products and technologies and well established, lower-cost public health technologies. Large regions of the world, however, including sub-Saharan Africa and parts of India, are still in this first stage of the epidemiologic transition.

During the age of pestilence and famine, CVD accounts for only 5%-10% of mortality, with the major forms of CVD related to infection and malnutrition -- largely rheumatic heart disease and the infectious and nutritional cardiomyopathies.[5]

Rising wealth and the resultant increase in the availability of food help open the door to the age of receding pandemics. Better nutrition decreases early mortality and perhaps reduces susceptibility to infectious diseases. Increased wealth allows for improvements in public health measures that contribute to further declines in infectious diseases. The change most characteristic of this phase is a precipitous decline in infant and child mortality accompanied by a substantial increase in average life expectancy. Examples of countries in this phase of the epidemiologic transition are the United States in the first few decades of the 20th century and China today.

During the age of receding pandemics, CVD accounts for 10%-35% of deaths. Types of CVD related to infection and malnutrition still predominate, along with emerging hypertensive heart disease and stroke. Coronary heart disease (CHD) rates tend to be low relative to stroke rates.

Continued improvements in economic circumstances combined with urbanization and radical changes in the nature of work-related activities lead to dramatic changes in diet, activity levels, and behaviors, such as smoking, that characterize the age of degenerative and man-made diseases. Cheaper, more plentiful, and higher-fat food leads to increased total caloric intake, while mechanization results in lower daily caloric expenditure. This disparity leads to a higher mean body mass index, plasma lipid levels, blood pressure, and blood sugar level -- changes that set the stage for the emergence of hypertensive diseases and atherosclerosis. As the average life expectancy increases beyond 50 years, mortality from largely chronic, noncommunicable diseases -- dominated by CVD -- exceeds mortality from malnutrition and infectious diseases.[5,6] Countries currently in this phase of the epidemiologic transition are the emerging market economies of the former Soviet socialist states and parts of the Middle East.

During the age of degenerative and man-made diseases, 35%-65% of all deaths are attributable to CVD. Rapid increases occur in the rates of hypertensive CVD, CHD, and peripheral vascular disease, with the rate of CHD deaths typically exceeding that of stroke by a ratio of 2-3 to 1.

In the final phase of the epidemiologic transition, CVD and cancer remain the major causes of morbidity and mortality. However, major technologic advances, such as coronary care units, revascularization procedures, and thrombolytic therapy are available to manage the acute manifestations of CVD, and preventive strategies, such as smoking cessation and blood pressure management, are widely implemented. As a result of better treatment and extensive primary and secondary prevention efforts, some deaths are prevented among those with disease and some primary events are delayed. Life expectancy creeps upward as age-adjusted CVD mortality continues to decline, with CVD affecting older and older individuals, on average.

During the age of delayed degenerative disease, age-adjusted death rates from CVD level off to below 50% of total mortality. The decline in stroke rates tends to precede the decline for CHD, and the ratio of CHD to stroke deaths typically increases to between 3:1 and 5:1 (Figure 2). As more individuals survive the acute manifestations of atherosclerotic disease, more people live longer with such cardiovascular diseases as angina pectoris, congestive heart failure, and cardiac arrhythmias.

Increase and decline in heart disease rates through the epidemiologic transition in the United States, 1900-1996From Achievements in public health, 1900-1999: decline in deaths from heart disease and stroke -- United States, 1900-1999. MMWR Morb Mortal Wkly Rep. 1999;48(30):649-656.

Because the epidemiologic transition is linked to economic, social, and demographic forces, it takes place at different rates in different countries, or even in different regions within countries. The established market economies (EstMEs) of Western Europe, North America, Australia, New Zealand, and Japan are largely in the fourth phase of the epidemiologic transition, with CVD accounting for 45% of all deaths in 1990 and communicable diseases accounting for well under 10% ( Table II ). The emerging market economies (EmgMEs), which include the former socialist states of Eastern Europe, are in the third phase of the transition, with CVD accounting for 54% of deaths in 1990. In the developing economies (DevEs), which can further be subdivided into six geographic regions -- China, India, other Asian countries and islands, sub-Saharan Africa, the Middle Eastern Crescent, and Latin America and the Caribbean -- 23% of deaths were due to CVD in 1990, while communicable diseases accounted for 42% of deaths. Across the six subgroups of the DevEs, however, there remains a high degree of heterogeneity with respect to the phase of the epidemiologic transition. In sub-Saharan Africa, communicable disease rates still far exceed those of chronic diseases, placing this region in the first phase (pestilence and famine). Some regions of India also appear to be in the first phase, while others are in the second or even the third phase. The Middle East appears to be in the third phase of the epidemiologic transition.

It is also important to note that these epidemiologic transitions occur at different rates across economic groups, generally beginning among individuals with higher socioeconomic status and eventually spreading to those with lower socioeconomic status. The decline in rates of malnutrition and communicable diseases, as well as the increase in coronary risk factors and behaviors, occur first in the privileged classes; higher rates of stroke and CHD soon follow. Later, as the middle class grows, the epidemiologic transition spreads to a broad enough sector of the population to have a measurable impact on population rates. People in lower socioeconomic strata tend to acquire the harmful risk factors last, in part because of their economic situation and in part because they tend to engage in more physical activity at work. Compared with people in the upper and middle socioeconomic strata, those in the lowest stratum are less likely to have access to advanced treatments and to acquire and apply information on modification of risk factors and behaviors. Thus, CVD mortality rates decline later among those with lower socioeconomic status. In Canada, for example, CVD mortality rates are highest among the poorest individuals (Figure 3).[7]

Cardiovascular disease (CVD) standardized mortality ratios by neighborhood income for Canadians of European ancestry, aged 35-74, in 1986 and 1991[7]

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