Dementia Rates Might Be Decreasing, And Scientists Have No Idea Why

Despite growing rates of obesity, diabetes and other diseases thought to increase the risk of dementia, America’s dementia rates are falling, according to a newly published national study of more than 21,000 diverse senior citizens.

An estimated 4 to 5 million seniors in the U.S. live with dementia, a broad term that describes a decline in memory and cognitive function and includes diseases like Alzheimer’s disease, Parkinson’s disease and dementia with Lewy bodies. Experts aren’t sure what causes dementia, but scientists have found that cardiovascular disease, diabetes and obesity all raise a person’s risk of cognitive decline. 

The study is the largest to date that finds dementia rates are decreasing, but it isn’t the first. It confirms what smaller studies among less diverse groups have already found in the past few decades. The researchers found that dementia decreased from 11.6 percent in 2000 to 8.8 percent in 2012 among surveyed U.S. adults 65 years or older, meaning that an estimated 1.5 million people expected to have dementia by now appear to have dodged the diagnosis, reports The New York Times. 

The data present a puzzling picture for researchers who don’t know if this is a fluke or if it will continue in the future. 

“We’re definitely not certain or even confident that the declining risk we saw over the last 25 years will continue to decline, level off, or start ticking back up,” said lead author Dr. Kenneth Langa, a professor of medicine at the University of Michigan and the Veterans Affairs Ann Arbor Healthcare System.

“People who are in their 40s and 50s now, on average, will have spent more time overweight and with diabetes than the people we were looking at in our cohort,” he continued. “There’s still some uncertainty about how these trends will affect dementia rates 10, 20 or 30 years from now.”  

One possible explanation highlighted by the study could be that people entering their mid-60s and older now have higher average rates of education, a marker linked to better cognitive health in old age. This could indicate that future generations, who are increasingly better educated, could maintain this decrease. 

How researchers measured dementia rates in the U.S. 

The researchers questioned 10,546 people living in community or nursing homes in 2000, and then questioned 10,516 respondents ― a mix of previously surveyed and new people ― again in 2012. The questionnaire included several tests that measured cognitive function. These tasks asked them to count backward from 20 or count backward from 100 in groups of seven (100, 93, 86). 

They found that the 2012 group had a 24 percent relative decrease in rates of dementia symptoms compared to the 2000 group. The 2012 group also had completed, on average, one more additional year of education compared to the 2000 group. However, the 2012 group also had higher rates of diabetes, obesity and other chronic diseases ― conditions thought to increase risk of dementia. The researchers concluded that education levels, as well as better control of chronic medical conditions that increase the risk of cardiovascular disease, may explain some of the decreased dementia risk. 

What the decrease means for Americans

The study’s results are welcome news because it suggests that lifestyle changes may be able to lower the risk of dementia, says Munro Cullum, a clinical neuropsychologist and Alzheimer’s disease expert at UT Southwestern Medical Center’s O’Donnell Brain Institute in Dallas, Texas. Cullum wasn’t involved in the analysis, but did say that the population trends are consistent with what scientists have been learning about cognitive health.

Put simply, “What’s good for the heart is good for the brain.” As Americans continue to avoid smoking and become more conscious about nutrition, the importance of exercise and the positive effect that education and mental stimulation can have on cognitive health, there is reason to hope that dementia rates ― and perhaps even absolute numbers ― will decrease in the future.

But Cullum also pointed out that America’s population is rapidly aging ― the oldest baby boomers turned 70 this year ― and this demographic shift may outpace the positive lifestyle changes that they and the rest of the nation are making.

Langa agrees. As baby boomers reach their mid-seventies and eighties, America will probably see an increase in the overall number of people with dementia, simply because of the population growth in this age demographic.

In a similar vein, the Alzheimer’s Association pointed out in a statement about the research that while rates may be decreasing, absolute numbers of people who develop dementia continue to increase as the population size increases. According to the organization’s 2016 report, the number of older Americans with some form of dementia is expected to increase from 5.2 million now to 13.8 million by 2050. Worldwide, those numbers will increase from 47 million to 131 million.   

“Obviously, we still see a lot of individuals presenting with symptoms of dementia, so our clinics are no less busy than they used to be,” Cullum said. “These are population trends we’re looking at, and how those actually filter down and apply to individual clinics, sites, states and institutions is a little bit less clear.”

While doctors can’t predict who will and won’t develop dementia as they age, there are a few things that people of all ages can do now to keep their brain healthy and strong. They include regular physical exercise, weight maintenance and a nutritious diet.

Langa has also studied a hypothesis called the “cognitive reserve,” which supposes the brain becomes resistant to the effects of damage through early and lifelong education and stimulation. Complex new challenges actually change the biology of the brain, he explained, and such challenges can come by way of education, job training and even leisure time hobbies.

“[Cognitive challenge] creates more connections between the nerve cells, more brain networks that are more able to withstand pathologies and problems that build up in the brain as people age,” he said. “Because the brain is better able to compensate, as people age, they’re able to continue thinking normally and have a lower risk of dementia.”

Several different kinds of studies support this concept. Observational studies like Langa’s new work find an association between more years of education attainment and a lower risk of dementia. Brain autopsies that compare people with low educational attainment and high educational attainment suggest that while education doesn’t appear to protect a brain from disease, it does seem to result in fewer dementia symptoms in the person’s final years than a person with less education.

However, like all things health-related, the relationships between certain lifestyle behaviors and eventual health outcomes are complex, difficult to pinpoint and offer no guarantee that a person may be able to avoid certain diagnoses later on in their life. For instance, Robert Sargent Shriver, Jr., a politician who founded the Peace Corps, went on to develop Alzheimer’s disease despite his lifelong love of learning and extraordinary intelligence. 

While the study shows dementia trends are going in a positive direction, Langa concluded a lot more research has to be done to understand why dementia develops in some people in the first place, and how we can avoid it. 

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