By Kate Kelland LONDON (Reuters) – 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. High blood pressure, also known as hypertension, puts extra strain on the blood vessels and major organs such as the heart, brain and kidneys.