The number of people with high blood pressure has almost doubled in 40 years to over 1.1 billion worldwide, researchers said on Wednesday.

“High blood pressure is the leading risk factor for stroke and heart disease, and kills around 7.5 million people worldwide every year,” said lead author Professor Majid Ezzati from Imperial College in London.

In the largest study of its kind analyzing blood pressure in every nation between 1975 and 2015, the scientists said that it has fell sharply in wealthy countries – possibly due to healthier diets and lifestyles – but risen in poorer ones, especially in Africa and South Asia, the researchers said.

Known as hypertension, high blood pressure puts extra strain on the blood vessels and major organs such as the heart, brain and kidneys, which made it the major cause behind cardiovascular disease that leads to strokes and heart attacks.

7.5 million deaths approximately are estimated worldwide to occur because of high blood pressure.

World Health Organization researchers working with hundreds of scientists internationally led the study which covered blood pressure measurements from nearly 20 million people and was published in The Lancet medical journal.

Ezzati said that without introducing “effective policies” to allow the poorest to improve their food management, mainly by dropping salt intake from their diets and making fruit and vegetables affordable, the WHO’s 2025 target of reducing high blood pressure cases by 25 percent was “unlikely to be achieved”.

In Europe, Britain had the lowest proportion of people with high blood pressure in 2015. South Korea, the United States and Canada had the lowest hypertension rates in the world, while over than half the world’s adults with high blood pressure in 2015 lived in Asia, the study estimated.

“High blood pressure is no longer related to affluence – as it was in 1975 – but is now a major health issue linked with poverty,” said Ezzati.