(CNN) The world is slowly seeing cancer surpass cardiovascular disease as the leading cause of death among middle-age adults in several countries, according to a new study.
Among adults ages 35 to 70, cardiovascular disease still ranks as the leading cause of death globally, but the new research, published in the journal The Lancet on Tuesday, found that deaths from cancer are now more common than those from cardiovascular disease in some high-income and middle-income countries.
Those countries include Sweden, Canada, Chile, Argentina, Poland and Turkey.
The study is the largest of its kind analyzing causes of death across five continents, said Dr. Salim Yusuf, distinguished professor and executive director at the Population Health Research Institute at McMaster University in Canada, who was senior author of the study.
"We have been watching the decline in cardiovascular disease for a while in many countries," he said. "It was just a matter of time that the progress we make in reducing cardiovascular disease mortality will lead to a fall in death rates from cardiovascular disease below that of cancers."
The researchers noted in the study that "this epidemiological transition" might be due to improved prevention and treatment of cardiovascular disease in high-income countries, whereas successful strategies to prevent and treat cancers, other than tobacco control, are yet to lead to large reductions in most cancers.
The study involved analyzing data on deaths and diseases among 162,534 adults across five continents. The data came from a research effort called the Prospective Urban Rural Epidemiology, or PURE, study and dated from 2005 to 2016.
The countries where the adults were from were separated into three categories.
There were low-income countries: Tanzania, Zimbabwe, Bangladesh, Pakistan and India. Then, middle-income countries: Philippines, Iran, South Africa, Colombia, China, Brazil, Malaysia, Turkey, Poland, Argentina and Chile. Lastly, high-income countries: Saudi Arabia, United Arab Emirates, Canada and Sweden. The study noted that there was no accurate estimate for income for Palestine, which was among the countries included.
After analyzing the data across those countries, the researchers found that non-communicable diseases, such as cardiovascular disease, were the most common cause of deaths and illnesses globally among the adults.
The researchers also found that cardiovascular disease was more common in middle-income and low-income countries than in high-income countries.
Meanwhile, there was a higher incidence of death from cancer than cardiovascular disease in high-income countries and some upper middle-income countries, according to the data.
In the high-income countries, "death from cancer was twice that from cardiovascular disease," the researchers wrote in the study. Whereas, in the low-income countries, "death from cardiovascular disease was three times that from cancer," they wrote.
Some of the same researchers also authored a separate study, published in The Lancet on Tuesday, that found most cardiovascular disease cases and deaths around the world are preventable and can be attributed to a small number of common modifiable risk factors.
The most important ones are "high blood pressure, tobacco and lipids -- and most surprisingly -- low education, low strength, and both indoor and outdoor pollution," said Yusuf, who was first author of that study.
Both studies had some limitations, including that even though they spanned five continents, they still did not include all countries around the world. More research is needed to determine whether the findings can be extrapolated to all countries globally.
The data within each income category may not be representative of all countries within those categories, "with particularly large gaps in information for countries in Africa and the Middle East," noted an editorial that published alongside the studies in The Lancet.
Stephanie Read, of Women's College Research Institute and Women's College Hospital in Toronto, and Sarah Wild, of the University of Edinburgh in the United Kingdom, co-authored that editorial.
Yet the new findings "can inform the effective use of limited resources—for example, by indicating the importance of improving education across the world and improving diet and reducing household air pollution in less developed countries," Read and Wild wrote.
"The value of collecting similar data to inform policy in a wider range of countries is clear, while improving lifestyle choices and modifying their social and commercial determinants remain a challenge," they wrote.
Even though the United States was not included in the new studies, separate research published last year in the journal Annals of Internal Medicine found that heart disease was more likely to be the leading cause of death in low-income counties nationwide, while cancer was the leading cause of death in many high-income counties.
"We are seeing a new epidemiologic transition -- from heart disease to cancer as the leading cause of death -- which is occurring first in high income communities," said Dr. Latha Palaniappan, lead author of that previous research and a professor of medicine at Stanford University Medical Center in California. She was not involved in the new studies.
"This is an important opportunity, both in our country and worldwide, to understand the factors that have led to the steep decline in heart disease in high-income populations," she said. "Our challenge going forward is to evenly apply these benefits to less advantaged populations."