The number of people with high blood pressure has almost doubled in 40 years to over 1.1 billion worldwide, scientists said on Wednesday, with the burden of the condition shifting from the rich to the poor.

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

The increases are especially significant in Africa and South Asia, the researchers said, and could be partly due to poor nutrition in childhood.