As NPR reported in May, the number of Americans with Alzheimer's disease is expected to triple by 2050. But studies published in the last two weeks based in European countries show signs of declining dementia.
Dr. Carol Brayne of England's Cambridge University led the research on the Britain-based study, published in The Lancet journal on Wednesday. That study compared data from more than 7,600 people in the early 1990s to a contemporary group with similar characteristics in the same areas.
"What we found was that there was lower prevalence," she says. "That is, the proportion of the population who met the diagnostic criteria had dropped fairly consistently across the age groups and across the genders as well."
In the original study in the '90s, 8.3 percent of people met all the criteria for dementia. In the new findings, that fell to just 6.2 percent.
Brayne says contributing factors likely include today's longer lifespan, better medical care and changing social factors, like better education.
On July 11, Lancet published a separate study on cognitive function, conducted in Denmark. Unlike Brayne's report, which assessed people 65 and older, the Danish research looks at people older than 90. The Danish researchers found "significantly better" cognitive and physical functioning in a group born in 1915 than people born in 1905.
"It adds to the confidence in thinking that there really is a change," Brayne says. "Perhaps we can revise our estimates for this cohort downwards."
In the United States, the picture is murkier, though. Brayne says populations as healthy and education as their Western European counterparts will probably experience a decline in dementia rates. But she also notes that the United States is much bigger and more diverse than Britain or Denmark, and therefore harder to predict.
The National Institute on Aging and the Alzheimer's Association have been cautious about responding to the two studies. Both organizations have released similar statements saying that though a smaller percentage of people may be getting dementia, the sheer size of the aging population in the U.S. means the total number of people with dementia and Alzheimer's will continue to rise.