Findings from the Prospective Urban Rural Epidemiology (PURE) study that aimed to evaluate differences in the incidence of common diseases, related hospital admissions, and related mortality in a large contemporary cohort of adults from 21 high-, middle-, and low-income countries across five continents are published in The Lancet. Among adults aged 35–70 years, cardiovascular disease is the major cause of mortality globally. However, in high- and some upper middle-income countries, deaths from cancer are now more common than those from cardiovascular disease, indicating a transition in the predominant causes of deaths in middle-age.
Understanding contemporary variations in the incidence of common diseases and deaths across countries at different economic levels is crucial to develop strategies to improve global health. Two epidemiological transitions might have affected global patterns of disease and death. First, previous studies have noted a reduction in deaths from communicable diseases and an increase in non-communicable diseases. Second, prevention and treatment of some non-communicable diseases have improved, particularly cardiovascular disease in high-income countries, which has led to marked reductions in deaths from cardiovascular diseases. However, fewer advances have been made in the treatment of other non-communicable diseases, such as cancers, and these advances have been more recent. Thus, the incidence of and mortality from different non-communicable diseases might be changing.
The PURE study is a prospective, population-based cohort study. The key outcomes were the incidence of fatal and non-fatal cardiovascular diseases, cancers, injuries, respiratory diseases, and hospital admissions. The study researchers calculated the age-standardised and sex-standardised incidence of these events per 1000 person-years.
The latest analysis assesses the incidence of events in 162534 participants who were enrolled in the first two phases of the PURE core study, between January 2005 and December 2016, and who were assessed for a median of 9.5 years.
During follow-up, 11307 (7.0%) participants died, 9329 (5.7%) participants had cardiovascular disease, 5151 (3.2%) participants had a cancer, 4386 (2.7%) participants had injuries requiring hospital admission, 2911 (1.8%) participants had pneumonia, and 1830 (1.1%) participants had chronic obstructive pulmonary disease (COPD).
Cardiovascular disease occurred more often in low-income countries (7.1 cases per 1000 person-years) and in middle-income countries (6.8 cases per 1000 person-years) than in high-income countries (4.3 cases per 1000 person-years). However, incident cancers, injuries, COPD, and pneumonia were most common in high-income countries and least common in low-income countries.
Overall mortality rates in low-income countries (13.3 deaths per 1000 person-years) were double those in middle-income countries (6.9 deaths per 1000 person-years) and four times higher than in high-income countries (3.4 deaths per 1000 person-years). This pattern of the highest mortality in low-income countries and the lowest in high-income countries was observed for all causes of death except cancer, where mortality was similar across country income levels.
Cardiovascular disease was the most common cause of deaths overall (40%) but accounted for only 23% of deaths in high-income countries vs. 41% in middle-income and 43% in low-income countries, despite more cardiovascular disease risk factors, as judged by INTERHEART risk scores, in high-income countries and the fewest such risk factors in low-income countries.
The ratio of deaths from cardiovascular disease to those from cancer was 0.4 in high-income, 1.3 in middle-income, and 3.0 in low-income countries, and four upper middle-income countries, in particular Argentina, Chile, Turkey, and Poland showed ratios similar to the high-income countries.
Rates of first hospital admission and cardiovascular disease medication use were lowest in low-income and highest in high-income countries.
If patterns of disease and related deaths in middle- and low-income countries follow those in high-income countries, cancer could become the most common cause of death in these countries in the next few decades. The high mortality in poorer countries is not related to risk factors, but it might be related to poorer access to healthcare. Although strategies to address cardiovascular disease in adults remain important, enhanced efforts to prevent and successfully treat cancer are crucial to reduce mortality rates.
The authors concluded that although cardiovascular disease continues to be the primary cause of death overall in adults aged 35–70 years in studied countries, it is no longer the most common cause of death in high- and several upper middle-income countries, where deaths from cancer are now more common than those from cardiovascular disease. Whether similar patterns occur in other high- and middle-income countries needs to be explored, but this finding appears to indicate a new epidemiological transition among the different categories of non-communicable diseases. It is likely that cancer will become the most common cause of deaths globally in a few decades.
The PURE study is an investigator-initiated study that is funded by the Population Health Research Institute, Hamilton Health Sciences Research Institute, the Canadian Institutes of Health Research (including through the Strategy for Patient-Oriented Research via the Ontario SPOR Support Unit), the Heart and Stroke Foundation (ON, Canada), the Ontario Ministry of Health and Long-Term Care, and by unrestricted grants from several pharmaceutical companies, with major contributions from AstraZeneca (Canada), Sanofi-Aventis (France and Canada), Boehringer Ingelheim (Germany and Canada), Servier Laboratories, and GlaxoSmithKline, and additional contributions from Novartis, King Pharma, and from several national and local organisations in participating countries.
Reference
Dagenais GR, Leong DP, Rangarajan S, et al. Variations in common diseases, hospital admissions, and deaths in middle-aged adults in 21 countries from five continents (PURE): a prospective cohort study. Lancet 2019 Sep 2. pii: S0140-6736(19)32007-0. doi: 10.1016/S0140-6736(19)32007-0. [Epub ahead of print]