The risk of developing dementia is decreasing for people with at least a high school education, according to an important new study that suggests that changes in lifestyle and improvements in physical health can help prevent or delay cognitive decline.
The study, published Wednesday in The New England Journal of Medicine, provides the strongest evidence to date that a more educated population and better cardiovascular health are contributing to a decline in new dementia cases over time, or at least helping more people stave off dementia for longer.
The findings have implications for health policy and research funding, and they suggest that the long-term cost of dementia care may not be as devastatingly expensive as policymakers had predicted, because more people will be able to live independently longer.
There are wild cards that could dampen some of the optimism. The study participants were largely white and suburban, so results may not apply to all races and ethnicities. Still, a recent study showed a similar trend among African-Americans in Indianapolis, finding that new cases of dementia declined from 1992 to 2001. The 2001 participants had more education, and although they had more cardiovascular problems than the 1992 participants, those problems were receiving more medical treatment.
Another question mark is whether obesity and diabetes, which increase dementia risk, will cause a surge in dementia cases when the large number of overweight or diabetic 40- and 50-year-olds become old enough to develop dementia.
In any event, in the next few decades, the actual number of dementia patients will increase because baby boomers are aging and living longer.
"You don't want to give the impression that the Alzheimer's or dementia problem is disappearing — it's not at all," said Dallas Anderson, a program director on dementia at the National Institute on Aging, one of two agencies that financed the study. "The numbers are still going up because of the aging population."
Still, he added, the new research shows that "what happens in a person's life becomes important."
"It's not just, 'Oh, it's in your genes. You're going to get it,'" he said. "You can take steps to postpone the disease."
The decline reported in the new study was strongest in vascular dementia, which is most directly linked to cardiovascular problems. Alzheimer's, the most common form of dementia, also declined, but the trend narrowly missed what researchers consider statistically significant.
Still, Maria Carrillo, chief science officer for the Alzheimer's Association, an advocacy group, said "this tells me there absolutely is hope for Alzheimer's" if a push for healthier lifestyles accompanies efforts to find dementia treatments.
Dementia experts and advocacy groups have long predicted that the number of Americans with dementia, now about 5 million, would triple by 2050. But a burst of fresh research in Europe, Canada and the United States has pointed to decreases in recent decades in more educated populations with better-controlled cholesterol, blood pressure, and heart and lung health.
"There's more studies suggesting that the risk is going down and we might have to rethink some of the projections of how big a problem dementia will be 30 years from now," said Dr. Kenneth Langa, a professor of internal medicine at the University of Michigan. On Saturday, he will present at an international conference preliminary results from another large study, which found that the prevalence of dementia in a more nationally diverse population declined by about 21 percent from 2000 to 2010.
Results like this suggest, he said, "that even without a big breakthrough in medication or a vaccine that would stop the Alzheimer's process, that we can do things that lower the risk of dementia long term."
The New England Journal research is considered especially strong because it looked at the emergence of new cases of dementia, or incidence, and is based on data from the Framingham Heart Study, a large collection of detailed health information that began in 1948 with participants from Framingham, Massachusetts, and has continued to follow them and their children and grandchildren.
Researchers evaluated the cognitive status of 5,025 people age 60 and older in four time periods beginning in 1977, and found a steady decline of about 20 percent in new dementia cases each decade. They also found that on average, people were older when they were found to have dementia: 80 years old in the 1970s, compared with 85 in the group evaluated 40 years later.
Significantly, the decline in new dementia cases, or incidence, occurred only with people who had at least a high school diploma. High school graduates were also the only ones whose cardiovascular health, except for obesity and diabetes, improved steadily over the same 40 years.
"Whether education is beneficial in itself or whether education is a marker for other things like poverty and unhealthy lifestyle, we didn't parse that out," said Dr. Sudha Seshadri, a neurologist at Boston University Medical Center and a senior investigator with the Framingham Heart Study.
Seshadri said the study did not yield strong evidence that college-educated people had even lower dementia risk, but with small numbers of college graduates in the study's early groups, it was hard to tell. The study led by Langa, which compared a nationally representative survey of about 10,000 Americans age 65 and over in 2000 to a similar group in 2010, found more college correlated with less dementia.
"We find the more education the better," said Langa, whose study indicated that people in 2010 averaged almost a year more education than those in 2000, and that education explained about half of the decline in dementia in that decade.
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.
"That's a major puzzle, what is the causal effect of education on dementia and cognitive function later in life," said Michael D. Hurd, the director of the RAND Center for the Study of Aging.
Hurd, who led a study in 2013 estimating that the cost of dementia care would more than double by 2040, said it was too early to say if that estimate should now be lower. Some people will be living longer with dementia, needing, say, 10 years of nursing home care, instead of three, he said, adding that "Framingham is not the U.S. population."
Indeed, another study published Wednesday found significant racial disparities, with African-Americans the most likely group to develop dementia, Asian-Americans the least likely, and whites and Latinos somewhere in between.
Not all of the Framingham results could be explained by education or cardiovascular health, Seshadri said, a reflection of the complexity of dementia.
Marie and Joe Porcello, study participants, are 86-year-old high school graduates with no significant cardiovascular problems or family history of dementia. But Joe Porcello remains healthy, while his wife, a retired secretary, developed dementia about 10 years ago and is in an assisted-living facility.
"I took care of her as long as I can, and then she fell one day when she was getting out of the bathtub," Joe Porcello said. He said his wife usually recognized him, but "the other day when I went up there, she said, 'Who are you?' and I said 'I'm your husband.' Then right away she knew who I was and she puckered up like she wanted to give me a kiss."
Joe Porcello, a retired phone company foreman, attended night school for postsecondary algebra classes, but "in my lifetime, you didn't really have to go to college," he said.
"Today, everybody has to go to college, or you end up pushing carts in supermarkets."
Their daughter Cynthia Johnson, 54, who received a bachelor's degree in computer science and worked as a software engineer, belongs to a generation that researchers would now predict to have less dementia.
But David Jones, a professor of the culture of medicine at Harvard, said history showed disease trends were rarely straightforward. Dementia, he said in an email, "won't be as bad as it would have been had incidence not begun to fall, but it will still be a very difficult problem."