Dementia Risk Builds Up Over a Lifetime — Scientists Are Mapping How

Researchers have studied many aspects of the human experience – across the entirety of a person’s lifespan – in efforts to explain why some people develop dementia and others don’t. They’ve linked education in childhood, food security in mid-life, and social interaction in older age to slower rates of cognitive decline.

Now, some scientists think that it’s necessary to combine all these factors to determine a person’s “social exposome” and to get the clearest possible picture of a person’s lifetime risk for dementia. Two recently published studies show different approaches researchers have taken to achieve this goal.

In the first, researchers at the University of Wisconsin connected lifetime housing records (where people lived) to brain injuries observed postmortem. In the second, a multinational team of scientists surveyed older adults in six Latin American countries about their life experiences and then tested their cognitive function. Together, the two studies highlight the value of considering as much information as possible when assessing someone’s risk for dementia.

“It is the interaction between your childhood experiences, between how you interact with people in your everyday life, the work that you do, the quality of your relationships,” Joaquín Migeot, a neuroscientist with the Latin American Brain Health Institute who led the study, told Being Patient. “All of these factors accumulate across the lifespan and can be predictive of dementia trajectories.”

Remembering all the risk factors

Migeot and his colleagues devised a set of over 300 questions to capture information about respondents’ education, financial status, healthcare, homelife, experience of trauma, and relationships. The respondents provided answers about three representative periods in their lives: 0 to 10 years old, 35 to 45 years old, and most recently. The answers were compiled into a single score.

Over 2,000 adults answered the questions and then took standard cognitive tests and underwent MRI scans. The study found that the score that encompassed the entire social exposome was the best way to predict the participants’ cognitive and structural changes. 

However, Migeot and his colleagues also noticed that the relative importance of the individual categories varied depending on a person’s dementia status. For people who did not have dementia, finances and educational attainment were most strongly associated with cognitive function. In contrast, all  categories had similar levels of importance for people diagnosed with Alzheimer’s disease or frontotemporal dementia.

In the future, Migeot hopes to develop a condensed question set to make it easier for clinicians to analyze a person’s social exposome and assess their risk of dementia. “But in order to do that, I will start with the basic assumption that it’s necessary to consider not just education and socioeconomic status, but also include questions about childhood experiences” and other subjective factors, he said.

Accumulating risk

Still, it’s not always easy for a person to recall detailed information about their entire life history – and it’s impossible to survey people who have already died and donated their bodies to dementia research centers.

That’s why Sarah Keller, a health disparities researcher at the University of Wisconsin, turned to housing and census data. She and her colleagues examined the brains of 740 people who had donated them to Alzheimer’s disease research centers; they hoped to relate any brain injuries they observed to differences in the donors’ social exposomes. 

To reconstruct the lives of the donors, Keller’s team used historic documents like obituaries, deeds, and marriage announcements. Then, after identifying each county in which the donors had resided over the course of their lives, the researchers used census data to learn about the poverty levels, educational attainment, and housing characteristics of those counties.

People who spent more time in counties that had higher rates of poverty and lower levels of educational attainment were more likely to have brain injuries indicative of deteriorating brain health. “The risk of vascular brain injury – these small changes in the brain – increased by about four percent every year,” Keller told Being Patient.

The period of time in which a person experienced hardship also mattered. People who moved from a more affluent area in their childhood to a more disadvantaged area in adulthood had a 12 percent higher risk for brain injuries.

Now, Keller plans to look at samples from additional centers with the goal of developing a more comprehensive picture of the risk that people in various parts of the United States have for developing dementia. She has high hopes that her efforts to understand the social exposome – as well as those of Migeot and other researchers around the world – will ultimately unlock new strategies for preventing dementia.

“Looking at these differences across the entire life course, we can target certain periods or target things before they start to build up over time,” she said.

Andrew Saintsing (@AndrewSaintsing) earned a PhD in biology, and now he writes about science for outlets like Drug Discovery News.