Cancer now the biggest killer in richer countries
Twin studies reveal ‘a new epidemiologic transition’.
Cancer is now the leading cause of death in high-income countries (HIC), but heart disease is still the biggest risk in low-income (LIC) and middle-income (MIC) countries, according to two reports published in the journal The Lancet.
Both stem from the Prospective Urban and Rural Epidemiologic (PURE) study, which followed 160,000 people in 21 countries for almost a decade, examining common disease incidence, hospitalisation and death, and modifiable cardiovascular risk factors.
They show that cardiovascular disease (CVD) is the leading cause of mortality among middle-aged adults globally, accounting for 40% of all deaths, but cancer is now responsible for twice as many deaths as CVD in HIC.
The lead author of the first report, Gilles Dagenais from Laval University, Canada, says the world “is witnessing a new epidemiologic transition among the different categories of non-communicable diseases”.
“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,” he says.
The researchers followed 162,534 adults aged 35 to 70 in four HIC, 12 MIC and five LIC between 2005 and 2016 and found that CVD-related deaths were 2.5 times more common in LIC compared with HIC, despite LIC experiencing a substantially lower burden of CVD risk factors compared with wealthier countries.
They suggest that higher CVD-related mortality in LIC may be mainly due to lower quality of healthcare, given that the report found first hospitalisation rates and CVD medication use to be both substantially lower in LIC and MIC, compared with in HIC.
Overall mortality rates were twice as high in LIC compared with MIC, and four times higher in LIC compared with HIC, though rates of deaths from cancer were similar across all country income levels.
The second report explored the relative contribution of 14 modifiable risk factors to CVD, among 155,722 middle-aged people without a prior history of CVD in the same 21 countries.
It shows that modifiable risk factors, including metabolic, behavioural, socioeconomic and psychosocial factors, strength and environment, account for 70% of all CVD cases globally.
However, the relative importance of risk factors for CVD cases and death varies widely between countries at different stages of economic development.
“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,” says Sumathy Rangarajan from Canada’s Population Health Research Institute, who coordinated the study.
“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.”
The authors of both studies acknowledge some limitations and say caution should be exercised in generalising results to all countries.
In particular, they say, PURE does not include data from west Africa, north Africa or Australia; the number of participants from the Middle East is modest; and data from LIC are predominantly from south Asia, with a few African countries.
However, they suggest that the inclusion of nearly 900 urban and rural communities from multiple countries in different regions of the world provides substantial diversity of risk factors and contextual variables and makes it likely that the results are more broadly applicable than most previous studies.
The countries involved were Argentina, Bangladesh, Brazil, Canada, Chile, China, Colombia, India, Iran, Malaysia, Pakistan, Palestine, Philippines, Poland, Saudi Arabia, South Africa, Sweden, Tanzania, Turkey, United Arab Emirates, Zimbabwe.