Don't misread this new report: the number of people expected to develop all types of dementia is still expected to skyrocket in the coming years, with estimates of more than 13 million older adults in the U.S. afflicted with Alzheimer's disease by 2050.
But the report offers what researchers call "cautious hope."
The analysis, based on data from the Framingham Heart Study (FHS), and published in The New England Journal of Medicine, suggests that the rate of new cases of dementia may be declining. Over a period from the late 1970s until the early 2000s, researchers report about a 20 percent reduction in dementia cases per decade. One potential reason: What's good for your heart is also good for your brain. And the report finds that among the Framingham study participants, at least, overall heart health has generally improved over the decades. (Though obesity and diabetes prevalences have not.)
Claudia Satizabal, the study's lead author and an instructor of neurology at the Boston University School of Medicine, said in an interview that "with this study, what we're showing is that we could potentially prevent some cases or delay the onset of [dementia] with improved cardiovascular health." But, she warned, while the study points to improved heart health as a potential factor in the improved dementia outlook, "we need more research to identify which other factors have contributed to this decline so that we can extend this beneficial trend."
Researchers began tracking cognitive decline and dementia in the FHS participants beginning in 1975 and into the present; for the current study they rely on data from about 5,000 participants. This analysis involved dividing the years into four time periods — the late '70s, late '80s, '1990s and 2000s. The researchers estimated the incidence of dementia at any given age in each of those periods for five years.
"We found that there has been a progressive decline in the incidence of all dementias," Satizabal said. "If we compare to the late '70s, we observe a decline of 22 percent in the late '80s, then a 38 percent decline in the 1990s and a 44 percent decline in the 2000s."
Notably, she said, the decline was more pronounced with a type of dementia caused by strokes. And also notably, the decline was only seen among participants with a high school diploma or above. Higher education, Satizabal said, can often be related to a better quality of life, and better vascular health overall.
Satizabal also noted that on average, participants were older at the onset of dementia as the decades progressed: 80 years old in the 1970s, compared with 85 in the 2000s.
The New York Times coverage of the study stressed the education findings — that the decline in dementia cases did not extend to those without a high school degree:
There are many theories about why education may help stave off dementia, including that it leads to better economic opportunity, which can propel healthier habits and better access to medical care. Another theory is that learning generates more neural connections, allowing brains to compensate longer when memory and cognitive functions falter.
Researchers acknowledge the potential downsides of the study, including the fact that the Framingham participants are largely white and suburban, meaning the results may not hold among the larger, more diverse U.S. population. The researchers also did not look at the effects of important variables, such as changes in diet and exercise, because that data wasn't collected in the early years of the Framingham study. Additionally, they say, gains may be mitigated by rising obesity and diabetes in the population.
Still, the study suggests that at this point, when there's no cure or even treatment for dementia, there still may be something individuals can do to improve their odds.
But they caution that at the moment, the huge numbers still loom.
Despite our observation of a declining trend in the age-specific incidence of dementia and the possible stabilization of dementia occurrence in Western Europe, the worldwide burden of dementia will continue to increase rapidly as the average life expectancy increases. This is especially true for the most economically vulnerable persons, the most elderly persons in high-income countries, and persons in low-to-middle-income countries, where the average life expectancy and the burden of vascular risk factors are increasing most rapidly.
Here are the specific numbers:
By 2025 the number of people age 65 and older with Alzheimer's disease is estimated to reach 7.1 million — a 40 percent increase from the 5.1 million aged 65 and older affected in 2015. By 2050, the number of people in this age population with Alzheimer's disease may nearly triple, from 5.1 million to a projected 13.8 million, barring the development of medical breakthroughs to prevent or cure the disease.
Globally, the World Health Association estimates that dementia currently afflicts about 47.5 million people; that number is projected to reach 75.6 million in 2030 and almost triple by 2050 to 135.5 million.