Where people live - and the air they breathe, green space they can access, and social and political conditions they experience - may play a major role in how the brain ages, according to a large international study recently published in Nature Medicine.
Researchers analyzed brain scans and health data from 18,701 people in 34 countries and found that combined environmental and social conditions were strongly linked to whether the brain appeared biologically older or younger than a person's actual age. The work included researchers from the University of Kentucky Sanders-Brown Center on Aging.
Rather than looking at one factor at a time, the researchers examined the "exposome" - the full range of environmental, social and contextual factors people are exposed to over their lives. These included air pollution, climate patterns, access to green space, water quality, poverty, education, inequality and civic participation.
When these factors were considered together, they explained far more differences in brain aging than any single factor alone and, in many cases, more than a person's clinical diagnosis, such as Alzheimer's disease.
"This study shows that brain health is shaped not only by biology and individual choices, but also by the broader environments people live in," said Yang Jiang, Ph.D., a professor in the Department of Behavioral Science in the UK College of Medicine and an affiliated faculty member at the Sanders-Brown Center on Aging. Jiang's lab is the only group in the United States contributing electroencephalogram (EEG) data to this brain clock study.
Using advanced brain imaging and machine learning tools, the team estimated each participant's "brain age" and compared it to their chronological age. A larger gap, where the brain appears older than expected, has been linked in previous research to cognitive decline and dementia risk.
The study found that physical environmental factors, such as higher air pollution, extreme temperatures and limited access to green space, were most strongly linked to structural changes in the brain. Social factors - including poverty, inequality, weaker democratic institutions and lower civic participation - were more closely associated with changes in how different brain regions communicate.
Importantly, these combined environmental and social pressures were linked to accelerated brain aging even in people without diagnosed neurological disease.
The findings suggest that efforts to promote healthy brain aging should go beyond individual lifestyle changes and medical care alone.
"Strategies that reduce air pollution, expand green spaces, strengthen education and reduce inequality may also support healthier brain aging," the authors wrote.
Sanders-Brown Center on Aging researchers have long studied how environmental and social factors affect cognitive health. A key contribution from the University of Kentucky to this study was a long-standing brainwave data set that Sanders-Brown researchers have been building and refining for more than two decades.
"This includes our founding director Dr. William Markesbery who referred more than a dozen Alzheimer's disease patients to this work. The cohort has continued to grow substantially thanks to the efforts of our current director of clinical trials Dr. Greg Jicha, and contribution from many M.D. and Ph.D. trainees in the UK College of Medicine," said Jiang.
The de-identified electrophysiological data, collected from many participants in the UK Alzheimer's Disease Research Center and related studies, represent one of the most unique, long-term brain aging resources of its kind in the United States. Jiang says this historical depth allowed the data from UK to meaningfully strengthen the global analysis by placing current brain aging patterns in a biological context.
The global study builds on that approach by showing how multiple exposures can interact and accumulate over time.
The study involved researchers from institutions across North America, Europe, Latin America, Africa, Asia and Australia and highlights the importance of studying brain health across diverse populations.
Research reported in this publication was supported by the National Institute on Aging of the National Institutes of Health under Award Numbers P01AG078116, P30AG072946 and K01AG000986.
