Predictions of a global dementia epidemic may have been exaggerated, with levels of the disease stable or even declining, scientists have revealed.
Researchers from the University of Cambridge reviewed five studies in the UK, Sweden, Spain and the Netherlands between 2007 and 2013, using consistent research methods and diagnostic criteria.
They found the number of people with dementia is about the same as it was two decades ago, despite sustained population ageing. During the nineties, it was predicted that 8.3 per cent of over-65s would now have dementia, but the number stands at just 6.5 per cent.
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"Our evidence suggests a relatively optimistic picture," said Carol Brayne, lead researcher and professor of public health medicine at Cambridge Institute of Public Health.
Charities have welcomed the findings but warned against complacency. Jeremy Hughes, chief executive of the Alzheimer's Society said that although the percentage of people in specific age groups could be falling, the overall number of people with dementia is still set to increase as more people live into their 80s and 90s.
"With no cure, few effective treatments and an economic impact exceeding that of cancer or heart disease, dementia remains the most critical health and social care challenge facing the UK," he told The Guardian.
There are widespread fears that dementia levels will soar as life expectancy grows, with Prime Minister David Cameron calling it one of the "greatest enemies of humanity". But scientists say these predictions were based on research that was carried out more than 20 years ago.
The apparent decline in numbers in the UK has coincided with an overall improvement in people's lifestyle, education and living standards.
"How to reconcile this relatively optimistic picture with what looks like panic on the part of governments, charities and the mainstream media?" Brayne and fellow Cambridge researcher Yu-Tzu Wu ask in The Conversation.
It comes down to the complexities involved in diagnosing the disease and changes in diagnostic criteria, they say. "The worsening epidemic message also fits well with consumer psychology and the recent history of over-medicalisation: fear, demand for a solution, and salvation."
Major healthcare and pharmaceutical companies stand to make a large profit from the disease. "It makes sense for them to play up the possibility of avoiding conditions associated with ageing."
