Cancer now the leading cause of death in rich countries, responsible for twice as many deaths as heart diseases
Cancer is now the leading cause of death in high-income countries, which indicates a transition in the predominant causes of deaths in middle-age. Cardiovascular disease (CVD) remains the primary cause of death among middle-aged adults across the world, but this is no longer the case in high-income countries, where cancer is now responsible for twice as many deaths as CVD, according to two reports from the Prospective Urban and Rural Epidemiologic (PURE) study.
Researchers say that as cardiovascular diseases (heart diseases, most common being heart attacks and strokes) reduce in many countries because of prevention and treatment, cancer deaths will likely become the leading cause of death globally in the future.
"The world is witnessing a new epidemiologic transition among the different categories of non-communicable diseases, with CVD no longer the leading cause of death in high-income countries. Our report found cancer to be the second most common cause of death globally in 2017, accounting for 26% of all deaths. But as CVD rates continue to fall, cancer could likely become the leading cause of death worldwide, within just a few decades," says the lead author of the first study, Dr. Gilles Dagenais, emeritus professor at Laval University, Quebec, Canada.
The research team found marked differences in the most common causes of death based on country income levels. In high-income countries (HICs), deaths from cancer (1.7 deaths per 1000 person-years) were about 2.5 times more common than those from cardiovascular disease (0.6 deaths per 1000 person-years).
In middle-income countries (MICs), deaths from cardiovascular disease (2.0 deaths per 1000 person-years) were slightly more common than those from cancer (1.6 deaths per 1000 person-years), whereas, in low-income countries (LICs), deaths from cardiovascular disease (4.2 deaths per 1000 person-years) were three times more common than those from cancer (1.4 deaths per 1000 person-years).
Therefore, the ratio of deaths from cardiovascular disease to those from cancer was 0.4 in HICs, 1.3 in MICs, and 3.0 in LICs. Four upper-MICs (Argentina, Chile, Turkey, and Poland) showed ratios similar to the HICs, according to the study.
"The implications are that in high-income countries, while continued efforts to prevent and treat CVD should continue, new efforts to reduce cancer are required," says Darryl Leong, the co-lead author of the study, and assistant professor of medicine at McMaster University.
Over 162,500 adults for a median of 9.5 years
The first report followed 162,534 middle-aged adults (aged 35-70) in four high-income countries, 12 middle-income countries, and five low-income countries, over a median of 9.5 years (between Jan 6, 2005 and Dec 4, 2016).
"During follow-up, 11,307 (7.0%) participants had died, 9,329 (5.7%) participants had cardiovascular disease, 5,151 (3.2%) participants had cancer, 4,386 (2.7%) participants had injuries requiring hospital admission, 2,911 (1.8%) participants had pneumonia, and 1,830 (1.1%) participants had chronic obstructive pulmonary disease (COPD)," says the study published in The Lancet.
The findings of the study — led by the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in Hamilton, Canada — were also presented at the European Society of Cardiology Congress.
The high-income countries, which were part of the analysis, include Canada, Saudi Arabia, Sweden, and the United Arab Emirates. The middle-income countries were Argentina, Brazil, Chile, China, Columbia, Iran, Malaysia, Palestine, Philippines, Poland, Turkey, and South Africa. The low-income countries were Bangladesh, India, Pakistan, Tanzania, and Zimbabwe.
In a pattern observed for all causes of death except cancer, the overall mortality per 1,000 person-years was lowest in HIC (3.4%), intermediate in MIC (6.9%) and highest in LIC (13.3%).
The study estimates that 55 million deaths occurred across the world in 2017, of which approximately 17.7 million were due to cardiovascular disease (CVD). While cardiovascular disease was the most common cause of deaths among middle-aged adults globally, accounting for 40% of all deaths, but that ranged from only 23% in HIC to 41% in MIC and 43% in LIC. Cancer was the second most frequent cause of death at 26% of deaths, but this proportion varied and was responsible for 55% of deaths in HIC, 30% in MIC and 15% in LIC.
"Cardiovascular disease occurred more often in LICs (7.1 cases per 1000 person-years) and in MICs (6.8 cases per 1000 person-years) than in HICs (4.3 cases per 1000 person-years). However, incident cancers, injuries, COPD, and pneumonia were most common in HICs and least common in LICs," state the findings.
"Overall mortality rates in LICs (13.3 deaths per 1000 person-years) were double those in MICs (6.9 deaths per 1000 person-years) and four times higher than in HICs (3.4 deaths per 1000 person-years). This pattern of the highest mortality in LICs and the lowest in HICs was observed for all causes of death except cancer, where mortality was similar across country income levels," the findings add.
Researchers say that CVD-related deaths were 2.5 times more common in middle-aged adults in LIC compared with HIC, even though low-income countries are experiencing a substantially lower burden of cardiovascular risk factors compared with wealthier countries.
According to the research team, higher CVD related deaths in low-income countries might be mainly due to the lower quality of healthcare. They explain that there is an inverse association between the use of hospital care and effective medication versus deaths, suggesting that lower-quality healthcare may be responsible, at least in part, for the higher mortality in poorer countries.
"The high mortality in poorer countries is not due to a higher burden of risk factors, but likely other factors, including lower quality and less healthcare," says Salim Yusuf, principal investigator of the study, and a professor of medicine at McMaster University.
He adds, "While long-term CVD prevention and management strategies have proved successful in reducing the burden in HIC, a change in tack is required to alleviate the disproportionately high impact of CVD in LIC and MIC. Governments in these countries need to start by investing a greater portion of their Gross Domestic Product in preventing and managing non- communicable diseases including CVD, rather than focussing largely on infectious diseases.”
Over 70% of CVD cases and deaths due to modifiable risks
More than 70% of cardiovascular disease and deaths around the world could be attributed to a small number of common but modifiable risk factors, shows the second related study. It looked at 14 modifiable risk factors to CVD, among 155,722 middle-aged people without a prior history of CVD, within the same 21 countries.
The 14 modifiable risk factors making up the 70% are metabolic factors such as hypertension, blood lipids, abdominal obesity; behavioural factors including smoking, diet, physical activity, alcohol consumption, salt intake, strength as shown by handgrip, psychosocial factors such as education and depression, and environmental factors such as indoor and outdoor air pollution.
The analysis indicates that metabolic risk factors were the largest contributory risk factor globally (41.2%), with hypertension (22.3%) as the leading factor within this group.
The second study, also published in The Lancet, found that some of the risks are the same around the world, such as hypertension or low education, but other risks vary by a country’s level of economic development, such as air pollution and poor diet, which impact health more in middle and low-income countries.
In middle and low-income countries, the risk factors of low education, poor diet, indoor air pollution from solid fuel use, and low strength were most important. Hypertension was found to be the largest factor among the metabolic factors; low education level was the single largest risk factor, and air pollution was the most important community-level risk factor, say researchers.
"While some risk factors certainly have large global impacts, such as hypertension, tobacco, and low education, the impact of others, such as poor diet, household air pollution, vary largely by the economic level of countries. There is an opportunity now to realign global health policies and adapt them to different groups of countries based on the risk factors of greatest impact in each setting," says Sumathy Rangarajan, who coordinated the study.
According to the team, health policies should focus on risk factors that have the most significant impact on averting CVD and death globally, with additional emphasis on the risk factors of greatest importance in different countries.
"It is clear the majority of cardiovascular disease cases, and deaths are accounted for by a small number of common and modifiable risk factors, these could be improved. What is notable is that several risk factors that have a large effect such as strength, low education, and indoor and outdoor air pollution that have been underappreciated in the past have turned out to be more important than others that we have paid much attention to such as obesity or salt," says Philip Joseph, a joint lead author of the paper, and an associate professor of medicine at McMaster University.