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The Shift From Heart Disease to Cancer as the Leading Cause of Death in High-Income Countries: A Social Epidemiology Perspective

A combination of increased prevention and improved medical treatment of cardiovascular disease (CVD) has allowed cancer to gradually replace heart disease as the leading cause of death in high-income countries (1). Although mortality from both diseases has decreased steadily in recent decades, CVD mortality has decreased more rapidly. A 2016 report from the Centers for Disease Control and Prevention concluded that cancer will become the leading cause of death in the United States by 2020 (2), and this shift has already occurred in some European countries (1). These changes are part of what has been referred to as the fourth stage of the epidemiologic transition: the age of delayed degenerative diseases. This stage was initially identified to characterize the striking decreases in mortality from ischemic heart disease in the late 1970s. It has recently been proposed that it may also be accompanied by an increase in chronic inflammatory diseases, cancer, metabolic disease, and neurodegenerative disorders (3). Social factors are inherently interconnected with the epidemiologic transition, and their role in the first 3 stages of the transition has been much discussed. The driving force behind the transition from the age of pestilence and famine to the age of manmade diseases is improvement in socioeconomic conditions, such as standards of living, health habits, hygiene, and nutrition. This transition occurs in parallel with a country's socioeconomic development. Furthermore, socioeconomic as well as sociodemographic factors strongly influence the progression of the transition in different segments of the country's population. This is most apparent in the progression between the third and fourth stages of the transition, where population dynamics plays a major role. One aspect of the fourth stage of the epidemiologic transition has been described as the diseases of affluence being transformed into the diseases of poverty. This happened first for cardiometabolic disorders: At the beginning of the 20th century, they were considered to be businessmen's diseases, but they became more common among disadvantaged persons by the end of the century, at least in high-income countries (4). The study by Hastings and colleagues in this issue provides another lens for interpreting the population dynamics related to the epidemiologic transition (5). The researchers examined sociodemographic differences in the transition from heart disease to cancer as the leading cause of death in the United States, with county median income used as a proxy for socioeconomic status. Despite the limitations of using such an aggregate measure of socioeconomic disadvantage at the individual or group level, they highlighted a larger decrease in mortality from heart disease in high-income counties and, within counties, among ethnic groups (non-Hispanic whites, Asian Americans, and Hispanics) that are generally more socioeconomically advantaged. The patterns of decreases in cardiovascular mortality translate to an earlier shift to cancer as the leading cause of death in more socioeconomically advantaged counties and ethnic groups, given that cancer mortality has decreased more slowly. As the authors discuss, these sociodemographic differences can likely be explained by trends in disparities in the prevalence of major risk factors for CVD, such as smoking, obesity, and diabetes. For example, between 1960 and 2015, the prevalence of smoking in the United States decreased from 39% to 6% among college graduates and from 46% to 23% among persons who did not complete high school (6). During a similar period, differences in obesity (defined as body mass index 30 kg/m2) by education remained largely stable, but the prevalence of class 3 obesity (body mass index 40 kg/m2) as well as type 2 diabetes is increasing more rapidly among persons with lower education levels (7). Of course, these large inequalities in the prevalence of smoking translate to large inequalities in smoking-related cancer mortality. However, some types of cancer remain more common among better-off persons, and there is a longer delay between exposure to the risk factor and disease occurrence and death for cancer than for CVD. In summary, population aging and larger decreases in age-specific mortality from cardiovascular and respiratory diseases among elderly persons, especially those who are better off socioeconomically, are important elements in the shift from heart disease to cancer as the leading cause of death. However, the effects of genetic testing, screening, and personalized treatment on cancer incidence and survival are unclear. Novel and expensive cancer therapies are being introduced, and if they are effective, they might contribute in the near future to increasing social inequalities in cancer survival, with better-off persons having more rapid decreases in mortality (8). Social disparities also exist in genetic testing (9) and cancer screening (10), and this may also contribute to future trends in social inequalities in cancer mortality. Finally, recent reports have also shown increases in mortality from cardiometabolic and neurodegenerative disorders. Further research examining the socioeconomic and demographic correlates of these new facets of the epidemiologic transition will help to refine mortality projections in the United States and around the globe.