Heart disease remains the leading cause of death in middle-aged adults worldwide. However, cancer isn't far behind, especially in wealthy countries. In fact, according to two new surveys published on September 3rd in the British scientific journal The Lancet, it is becoming the main cause of death in high-income countries. Indeed, "cancer is likely to become the world's leading cause of death" in a few decades, according to the researchers.From 2005 to 2016, the authors of these surveys studied a sample of 160,000 adults in 21 high, middle and low-income countries. In 2017, heart disease accounted for more than 40% of deaths, or about 17.7 million people, while cancer caused just over a quarter (26%) of all deaths. But in wealthy countries, the results are alarming: cancer now kills 2.5 times more people than heart disease.In low-income countries, cardiovascular disease remains the number one killer, killing three times more people than cancer does. Yet people in low-income countries are less at risk of developing cardiovascular disease.How do you explain this paradox? Access to - and the quality of - the healthcare provided to these populations simply aren't as good as in rich countries.