A major, USC-led study of more than 214,000 older adults across 14 countries and regions finds that the most common controllable risk factors for dementia — such as low education, high blood pressure and smoking — vary widely from country to country, meaning a one-size-fits-all approach to prevention won’t work everywhere.

The findings appeared Sunday in the journal The Lancet Healthy Longevity.

Most of what scientists know about preventing dementia comes from research in wealthy countries such as the United States and those in Western Europe. But this study, led by researchers at USC along with colleagues at Brown University and Johns Hopkins University, set out to see whether those same patterns hold true in low- and middle-income countries.

Differences — and similarities — in dementia risk factors

The differences were striking — but so were the similarities:

• Differences: Low education affected 86% of older adults in China but only 12% in the United States, while high BMI (a measure of excess body weight) affected 45% of Americans compared to just 13% of people in India.
• Similarities: Certain risk factors tended to cluster together in similar patterns worldwide, such as cardiovascular risks (for example, high cholesterol and hypertension) or risky behaviors (such as smoking and drinking).

Lead author Emma Nichols, a research scientist with the Center for Economic and Social Research at the USC Schaeffer Institute for Public Policy & Government Service, says the consistency of these clusters was the most unexpected part of the findings.

“I was less surprised by the differences and more surprised by some of the similarities, particularly in the ways these risks are patterned across settings,” Nichols said. “That has real implications for how we design prevention strategies and interventions, because some things are more consistent across places than we might expect.”

For the study, researchers from the Gateway to Global Aging Data team combined harmonized survey data from long-running aging studies in 14 places — the United States, Brazil, China, England, India, Ireland, Korea, Malaysia, Mexico, Northern Ireland and four regions of Europe — collected between 2009 and 2023. (Jinkook Lee of the Center for Economic and Social Research at the USC Schaeffer Institute is principal investigator of the Gateway to Global Aging Data project as well as the Longitudinal Aging Study in India.)

They analyzed 12 modifiable risk factors identified by the Lancet Commission on dementia — things such as hearing loss, depression, physical inactivity and social isolation, comparing how common each factor was; how they varied by age, gender and education level; and how often multiple risk factors showed up together in the same person.

Dementia risk factors help guide decision-making

The researchers say the findings should help guide decision-makers and health organizations in designing dementia-prevention strategies tailored to their own populations. For example, a program that connects people to care for diabetes could be redesigned to address the entire cluster of related cardiometabolic risks, such as high cholesterol and hypertension, at the same time.

For the average person, Nichols adds, the takeaway is that dementia risk is not fixed or fated: “Risk for these late-life outcomes isn’t predetermined. These are risk factors you experience over the life course, and you can have an impact on changing your own risk — while also recognizing the ways broader societal factors shape that risk, too.”

Future work may also expand to include newer risk factors such as poor sleep and additional countries as more harmonized data becomes available; new data collection is already underway in additional countries, including Kenya and Egypt.

About the study: In addition to Nichols, other authors include senior author Jinkook Lee, Michael Markot, Drystan Phillips and Jenny Wilkens, all of the Gateway to Global Aging Data team at the Center for Economic and Social Research at the USC Schaeffer Institute; co-first author Zachary Kunicki of the Warren Alpert Medical School of Brown University; and Alden Gross of the Johns Hopkins Bloomberg School of Public Health.

This research was supported by the National Institutes of Health (grant R01AG030153).