It's a victory for medical science that deaths from cardiovascular disease (CVD) or heart disease are falling in a number of rich nations. But CVD is being replaced by cancer as the top cause of deaths in a number of these countries.

And that's a whole new challenge altogether.

A study, published in the peer-reviewed journal The Lancet, Tuesday, found cancer is moving past CVD as the leading cause of death among middle-age adults in a number of countries. The study is the largest of its kind, analyzing causes of death across five continents.

It revealed among adults ages 35 to 70, CVD remains the leading cause of death globally. On the other hand, deaths from cancer are now more common than those from CVD in some high-income and middle-income countries. These countries include Argentina, Canada, Chile, Poland, Sweden and Turkey.

"We have been watching the decline in cardiovascular disease for a while in many countries," Dr. Salim Yusuf, senior study author, a distinguished professor and executive director at the Population Health Research Institute at McMaster University in Canada, 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."

According to the study, "this epidemiological transition" might be due to improved prevention and treatment of CVD in rich countries. It noted successful strategies to prevent and treat cancers have yet to lead to large reductions in most cancers.

After analyzing the massive amount of data at their disposal, researchers found that noncommunicable diseases such as CVD were the most common cause of deaths and illnesses among adults worldwide. They also found CVD was more common in low-income and middle-income countries than in high-income countries.

Conversely, there was a higher incidence of death from cancer than CVD in high-income countries and some upper middle-income countries. In high-income countries, "death from cancer was twice that from cardiovascular disease," according to the study.

In the low-income countries, "death from cardiovascular disease was three times that from cancer.”

Figure A is an overview of a heart and coronary artery showing damage (dead heart muscle) caused by a heart attack. Figure B is a cross-section of the coronary artery with plaque buildup and a blood clot. U.S. National Heart, Lung and Blood Institute

The study analyzed data on deaths and diseases among 162,534 adults across five continents. The data was derived from the Prospective Urban Rural Epidemiology (PURE) study and covered the period from 2005 to 2016.

Adults in countries covered by PURE were grouped into three categories.

The low-income countries consisted of Bangladesh, Pakistan, Tanzania, Zimbabwe and India. Middle-income countries were the Philippines, Iran, South Africa, Brazil, Malaysia, Colombia, China, Turkey, Poland, Argentina and Chile.

High-income countries consisted of Saudi Arabia, the United Arab Emirates, Canada and Sweden.

The United States was not included in the new study.