A new study has found that dementia rates among people 65 and older in England and Wales have plummeted by 25 percent over the past two decades, to 6.2 percent from 8.3 percent, the strongest evidence yet of a trend some experts had hoped would materialize.
Another recent study, conducted in Denmark, found that people in their 90s who were given a standard test of mental ability in 2010 scored substantially better than people who reached their 90s a decade earlier. Nearly one-quarter of those assessed in 2010 scored at the highest level, a rate twice that of those tested in 1998. The percentage severely impaired fell to 17 percent from 22 percent.
The British study, published on Tuesday in The Lancet, and the Danish one, which was released last week, also in The Lancet, confirmed something that researchers on aging have long suspected but lacked good evidence to prove: dementia rates would fall and mental acuity improve as the population grew healthier and better educated.
Epidemiologists have found associations between various health measures and risk of dementia. Incidence is lower among those who control their blood pressure and cholesterol, for example, and it is lower among those who are better educated. Since some dementia is caused by ministrokes and other vascular damage, it made sense that as populations control these risk factors better, dementia rates might drop. But few studies were rigorous enough to put the hypothesis to a test.