As people live longer, many fear that there will be a rise in dementia cases. But the so-called “dementia time bomb” may not be as severe as once thought.
In 2013, two major studies in the UK observed a decline in dementia among the elderly over a 20-year period. Researchers first interviewed 7,500 people aged 65 and up in the UK in the early 1990s and then repeated the exercise two years later. They looked at a similar sample 20 years later—some 7,500 people from the same areas—with, like before, a repeat interview two years later.
“When we saw the prevalence has decreased, we didn’t know whether that was due to a fall in incidence [of new cases] or a decrease in survival,” says Fiona Matthews, professor of epidemiology at Newcastle University.
To investigate further, Matthews and her colleagues went back to these cohorts to re-examine the incidence rate. They re-interviewed the two groups of people, and noted the number of people who have died since the last research.
The study, published this week in Nature Communication, confirmed that dementia rates have been falling—by an average of around 20% over a 20-year period. But the average masks are a more interesting trend: the reduction was predominantly observed in men.
In the 1990s, for every 1,000 men aged 70-74, 12.9 developed dementia within a year. Twenty years later, that figure dropped to 8.7. The reduction was even more dramatic for men aged 65-69, as the relative number of new dementia cases more than halved over the same period.
For women, the reduction in the dementia rate was far more modest. Women aged 65-69 saw dementia cases drop from 6.3 per 1,000 women to 4.6 over 20 years. Meanwhile, the incidence rate went up slightly for women aged 80-84: from 35.6 per 1,000 during the 1990s to 39.6 in the later cohort.
While researchers can’t be sure why dementia rates are falling, Matthews suspects it may have something to do with public health policy, which has pushed people to stop smoking and consider their heart health.
“Cardiovascular risk is really crucial,” Matthews explains. “What’s good for your heart is good for your head.”
There’s also no clear reason why the decrease in dementia is seen predominately in men. That said, the study echoes previous research: The burden of dealing with dementia falls mostly on women. A report by Alzheimer’s Research UK highlighted how not only are more women affected by dementia, but they’re also much more likely than men to be caring for someone with dementia, which can take a toll on their own mental health.
“The burden of dementia has always fallen disproportionately on women because women live to an older age,” Matthews says. But as more men live longer too, the next step for researchers is to figure out why their brains seem less prone to dementia at advanced ages.