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, a trend that researchers say is likely occurring across developed countries and that could have major social and economic implications for families and societies.
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, soften alarms sounded by advocacy groups and some public health officials who have forecast a steadily rising population of baby boomers with the same odds of getting dementia as older people now, as well as exploding costs to care for them.
And experts on aging say the studies confirmed something they long suspected but lacked good evidence to prove: that dementia rates would fall and mental acuity improve as the population grew healthier and better educated. The studies’s findings may also give new impetus to efforts to get people to quit smoking and take other steps to lower their risks of heart disease and stroke.
Epidemiologists have long found that the incidence of dementia is lower among the better educated, as well as among those who control their blood pressure and cholesterol. Since some dementia is caused by ministrokes and other vascular damage, it made sense that as populations better control these risk factors, dementia rates might drop. A half dozen previous studies hinted that the hypothesis was correct but had methodological problems that cast doubt on such findings.
But researchers say the two new studies are the strongest, most credible evidence yet that their hunch was right. Dallas Anderson, an expert on the epidemiology of dementia at the National Institute on Aging, the principal funder of dementia research in the United States, said the new studies were “rigorous and are strong evidence.” He added that he expected the same trends were occurring in the United States but that studies were necessary to confirm them.
“It’s terrific news,” said Dr. P. Murali Doraiswamy, an Alzheimer’s researcher at Duke University, who was not involved in the new studies. It means, he said, that the common assumption that every successive generation will have the same risk for dementia does not hold true.
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