Researchers suggested the increase is due to population growth and an ageing population.

They assessed the four risk factors associated with dementia - smoking, obesity, high blood sugar and low education - and the impact they will have on future trends.

Improvements in global education access are projected to reduce dementia prevalence by 6.2 million cases but this will be countered by anticipated trends in obesity, high blood sugar and smoke, which are projected to result in an additional 6.8 million dementia cases, researchers suggested.

Where will the increases be?

Dementia cases are expected to rise in every country, with the smallest estimated increases in the high-income Asia Pacific (53%) and western Europe (74%), the study suggests.

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According to the estimates, the largest growth will be in North Africa and the Middle East (367%) and eastern sub-Saharan Africa (357%).

In the UK, the number of dementia cases is projected to increase by 75%, from just over 907,000 in 2019 to almost 1.6 million in 2050, while in western Europe, the number of dementia cases is expected to rise by 74%, from almost eight million in 2019 to nearly 14 million in 2050.

Relatively small increases in cases are expected in Greece (45%), Italy (56%), Finland (58%), Sweden (62%), and Germany (65%).

The Global Burden of Disease study is the first to provide forecasting estimates for adults aged 40 and older across 195 countries worldwide.

A focus on prevention

The experts are calling for more aggressive prevention efforts to reduce dementia risk through lifestyle factors, such as education, diet and exercise.

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Lead author Emma Nichols, from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington in America, said: "Our study offers improved forecasts for dementia on a global scale as well as the country level, giving policymakers and public health experts new insights to understand the drivers of these increases, based on the best available data.

"At the same time, we need to focus more on prevention and control of risk factors before they result in dementia. To have the greatest impact, we need to reduce exposure to the leading risk factors in each country."

Across the world, more women are affected by dementia than men.

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In 2019, women with dementia outnumbered men with dementia 100 to 69, and this pattern is expected to remain in 2050.

Co-author Dr Jaimie Steinmetz, from the IHME, said: "It's been suggested that Alzheimer's disease may spread differently in the brains of women than in men, and several genetic risk factors seem related to the disease risk by sex."

The authors acknowledge that their analysis was limited by a lack of high quality data in several parts of the world, and by studies using different methodologies and definitions of dementia.