There was an estimated 20% drop in the rate of new dementia cases in England and Wales in the 20 years up to 2011, a paper published today in the journal Nature Communications has found.
Researchers interviewed almost 8,000 people over the age of 65 across England and Wales between 1989 and 1994, focusing on three main areas – Cambridge, Newcastle, and Nottingham. Two years after the original interviews, they followed up to see how many people had developed dementia.
The team then interviewed over 5,000 people 20 years later, between 2008 and 2011, and found that the proportion of people developing dementia in that time was lower than 20 years previously.
The authors estimate that in the UK there are now just under 210,000 new cases of dementia per year, with around 135,000 of those in women and 74,000 in men.
"It's the strongest evidence yet to support that the prevalence of dementia by age group is not going up, and is possibly going down," Claudia Cooper, a reader in psychiatry at University College London who was not involved in the study told BuzzFeed News. "This shows that the risk for an individual is not going up."
While diagnosis rates are increasing, that's because we're getting better at spotting the condition.
"When we did the first interviews, we'd make a diagnosis [of dementia] and many of those people would not be known to services because they would have been coping perfectly well," Carol Brayne, a professor of public health medicine at the University of Cambridge and lead author of the study, told BuzzFeed News.
That's changed a lot in the last 20 years, she said, so if you look at the number of people being diagnosed, you'd think there was a big increase in the number of cases. "Or if you used mortality data, you'd think there was a big increase, because people have been putting on death certificates far more than they used to," she said.
The drop in new cases comes mainly from men across all age groups, but the study can't explain why.
But that doesn't mean there was no change at all in women. "In women, apart from in one age group, you do see a reduction," said Brayne. "It's not significant, so it evens out, but its not as simple as saying there's no change."
The reason for the much bigger change in men isn't clear, but could be down to environmental changes. John Hardy, a professor of neuroscience at University College London, who was not involved in the study, told the Science Media Centre that "the most obvious changes relate to vascular health … smoking cessation and blood pressure and cholesterol control." But more research will be needed to know either way.
Cooper also speculated that is might be down to the way we monitor vascular health more closely these days, but emphasised there was no way to know for sure without more research. "There have been big changes to the way vascular risk factors [for dementia] are dealt with," she said. "We treat cholesterol now, we monitor blood pressure – 40 years earlier that probably didn't happen so much."
The study shows that there are things we can do, as a society, to stave off dementia.
But it's more about large-scale changes than individual choices people make, Brayne said. "We call it the 'behavioural environment' because 'lifestyle factors' implies some sort of choice," she said. "And most of the things we do are not driven by choice, they're driven by environment.
"These cohorts have very different exposure to educational levels, to the simple fact of having an NHS. Our earlier cohorts would talk about siblings dying of diphtheria and so on – so there's a huge different in the health across the life course."
One finding from an earlier study by Brayne and her colleagues is that deprivation is associated with increased risk of dementia. "I think that's something we need to pay attention to, and in fact Public Health England is paying attention to it," she said. "But it's not so much our individual life choices in mid-life and early life, it's more about how we structure everything we do across the life course for populations."
Simon Ridley, director of research at Alzheimer’s Research UK, said in a statement that the findings were "welcome news" but stressed that we should not be complacent.
"A growing body of evidence is now telling us that dementia risk across the population can change over time: an important reminder that dementia is not inevitable and can be fought," he said.
"The challenge for research now is to understand what has driven the reduction, so that we can capitalise on this knowledge and take action to prevent incidence rates rising again in future. Further research is also vital to determine why the reduction has been greater for men than for women, and how we can address this imbalance."