A study suggests the proportion of elderly people developing dementia is falling in the US – backing up similar findings in the UK and Europe.
Data from 21,057 people over the age of 65 in the US showed the proportion with dementia fell from 11.6% in 2000 to 8.8% in 2012.
One expert said the findings, published in the journal JAMA Internal Medicine, were “incredibly important for the world”.
According to the 2015 World Alzheimers Report, Australia and New Zealand face a 40% increase in the cost of dementia care by 2020. That is far higher than the global average of 35%.
The worldwide cost of care is estimated to skyrocket from $US818b to $US1 trillion in three years.
It is estimated that 353,800 Australians and 50,000 New Zealanders were suffering with dementia illnesses in 2015. Without a medical breakthrough, those figures are predicted to reach 900,000 and 150,000 respectively in the year 2050.
Similar studies in Europe, published in the Lancet Neurology last year, suggested dementia rates had fallen in the UK and among Spanish men and had stabilised in other European countries.
Professor Kenneth Langa, who conducted the latest study at the University of Michigan, said: “Our results add to a growing body of evidence that this decline in dementia risk is a real phenomenon, and that the expected future growth in the burden of dementia may not be as extensive as once thought.”
The slow decline in brain function is irreversible – there are no drugs or treatments – so finding ways of preventing the condition is hugely important.
Education has long been suspected to play a role, and the study found that while the dementia rate fell, the average time older adults had spent in school or university increased from 11.8 years in 2000 to 12.7 years in 2012.
It is possible that the mental challenge of education helps protect brain cells from dying later in life, or that once neurons start to die, education helps the rest of the brain rewire and compensate to prevent the symptoms of dementia appearing.
Good physical health is also thought to help protect the brain.
However, the study showed levels of diabetes, obesity and high blood pressure all increased between 2000 and 2012.
It is possible that better medication dampened their negative impact.
Professor Carol Brayne of the University of Cambridge, who conducted the European analysis, said the US study added “strong further evidence” that rates were declining in some countries.
Education appeared to be significant and people with higher levels of education seemed to “defer” dementia until later in life.
She told the BBC News website: “These findings are incredibly important for the world and underlie the importance of access to education.
“But it is likely to be a combination of risk factors – better health from conception, vaccinations, access to education, medical care, not smoking – that taken together will have an impact.”
Brayne added that identifying what could help stave off dementia would ensure “we don’t go backwards, otherwise the gains we’ve had won’t be had by future generations”.
However, the number of people affected could still soar. The falling rate could be overwhelmed by the rising numbers of people living into old age.
