Cardiovascular disease (CVD) is the major cause of death among middle-aged adults around the world; however, in high-income countries deaths from cancer have become twice as frequent as those from CVD.

The findings come from the first large prospective international study documenting the frequency of common diseases and death rates in high-, middle- and low-income countries using a standardized approach.

The research, published in The Lancet today and presented at the European Society of Cardiology Congress, is from the Prospective Urban Rural Epidemiology (PURE) study led by the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in Hamilton, Canada.

For this paper, the research involved more than 162,500 adults aged 35 to 70 from 21 countries who were followed for a median of 9.5 years.

"The fact that cancer deaths are now twice as frequent as CVD deaths in high-income countries indicates a transition in the predominant causes of death in middle age," said Salim Yusuf, principal investigator of the study, executive director of PHRI and a professor of medicine at McMaster.

"As CVD declines in many countries because of prevention and treatment, cancer mortality will likely become the leading cause of death globally in the future.

"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 health care."

The high-income countries (HIC) in the study were Canada, Saudi Arabia, Sweden and United Arab Emirates. The middle-income countries (MIC) were Argentina, Brazil, Chile, China, Columbia, Iran, Malaysia, Palestine, Philippines, Poland, Turkey and South Africa. The lower-income countries (LIC) were Bangladesh, India, Pakistan, Tanzania and Zimbabwe.

Yusuf added that the results are likely to be applicable to other countries with similar economic and social characteristics and health care.

In a pattern observed for all causes of death except cancer, overall mortality per 1,000 person years was lowest in HIC (3.4%), intermediate in MIC (6.9%) and highest in LIC (13.3%).

Regarding deaths, CVD was the commonest cause overall at 40%, but that ranged from only 23% in HIC to 41% in MIC and 43% in LIC, even though the CVD risk factors were highest in the HIC and lowest 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.

The other major findings of the study were:

• With higher country income, a higher proportion of deaths and hospitalizations were from non-communicable diseases compared to infectious diseases;
• The higher rates of CVD and related deaths in poorer countries compared to richer countries occurred despite much lower CVD risk factors in poor countries;
• There is an inverse association between use of hospital care and effective medication versus deaths, suggesting that lower quality health care may be responsible, at least in part, for the higher mortality in poorer countries.

"The implications are that in HIC, while continued efforts to prevent and treat CVD should continue, new efforts to reduce cancer are required," said Darryl Leong, the co-lead author of the study, scientist at PHRI, and assistant professor of medicine at McMaster University.

Gilles Dagenais, professor emeritus of medicine at Laval University and lead author of one of the PURE papers, added: "If ways of lowering CVD deaths that have been effective in high-income countries are implemented in middle- and lower-income countries, we could expect large drops in CVD deaths there as well over time. If that happens, we might also expect that cancer will become relatively more common as a cause of death."