The risk of DEMENTIA has almost halved in 30 years, as the British adopt healthier lifestyles, says the research.
Quitting smoking, eating well and staying physically and mentally active helped reduce the chance of developing the disease.
Millions of people also take statins and blood tablets that protect heart and brain health. But the increase in obesity and diabetes rates could reverse the downward trend, the experts fear.
The latest research has analyzed studies on almost 60,000 adults in Europe and America between 1988 and 2015.
At that time, 5,133 developed dementia but the rates dropped "around 15% every decade", the
The Alzheimer conference's Research UK in Harrogate, North York, was told.
Chief researcher Albert Hofman, of the American Harvard public health school, said the results are "positive" and more pronounced in men than women.
He said the fall "could be driven by changes in cardiovascular risk factors and lifestyle".
But he warned: "With other risk factors for dementia such as obesity and diabetes increasing, this apparent decline in dementia rates may not continue for long."
Some 850,000 Britons have dementia with numbers that should reach one million within a decade, as people live longer.
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There is no cure, but medications can limit its effects.
Dr. Carol Routledge, of Alzheimer's Research UK, said that while no drug can slow or stop Alzheimer's, there is "solid evidence of what is good for the heart is also good for the brain".
He added: "In addition to maintaining healthy blood pressure, the best current evidence suggests not smoking, drinking only within the recommended limits, staying mentally and physically active, following a balanced diet and keeping cholesterol under control can help maintain our healthy brains as we age. "