Global Study Links Environment and Social Conditions to Brain Aging

Where we live and what we experience have a major impact on the aging brain. But until recently, it was impossible to measure the cumulative impact of all these factors, which scientists call the exposome, on brain health. 

The exposome includes both physical exposures — like air pollution, green space, and temperature —  and social exposures — like democracy, socioeconomic equality, and economic stability. 

A new study published in Nature Medicine examined the impact of exposure to more than 70 different factors that make up the exposome across 34 countries. Exposure to these factors could increase the risk of accelerated brain aging by about three to nine times, impacting the brain’s age in a way that’s comparable or greater than some neurodegenerative diseases. 

One of the study’s authors, neuroscientist Hernán Hernández of the Universidad Adolfo Ibañez in Chile, told Being Patient the findings show “the environment in which we live can influence brain aging as much as, or even more than, disease.”

How the exposome accelerates the brain’s aging

The team of 142 international researchers analyzed data from more than 18,000 participants across Africa, Europe, Latin America, North America, Asia, and Oceania. One third of the participants had mild cognitive impairment (MCI), Alzheimer’s, or frontotemporal dementia (FTD).

The participants underwent MRI scans that allowed the researchers to assess their brain structure — the natural shrinkage of brain regions that occurs with age. Other forms of imaging provided measures of brain function, or how different brain areas light up and respond to different situations. Some functions, like cognitive processing speed and memory, start to decline with age. 

Putting this data into an algorithm gave the researchers a predicted brain age for each participant which could be compared against their actual age. 

The team also collected information about 73 exposomal factors in each country. Physical exposome factors included air pollution, green spaces, and temperature, while the social exposure factors included measures of socioeconomic equality, the country’s economic stability, and unemployment. 

The adverse exposomal factors sped up brain aging. That meant a bigger gap between predicted brain age and chronological age. Some of the most important predictors of accelerated brain aging were factors that are more difficult to control, like mean precipitation, levels of democracy, and other socioeconomic factors. 

The physical exposome, which includes reduced access to green spaces and higher levels of air pollution, was linked to faster structural brain aging. Meanwhile, the social exposome, especially those relating to democratic representation and rights, as well as socioeconomic indicators, were linked to faster functional aging. 

Compared to healthy controls, the brains of those with MCI, Alzheimer’s or FTD, showed more accelerated brain aging driven by the exposome. Higher levels of carbon emissions, mean temperature, and corruption in the place where the person lived were the most important predictors of these disorders. 

Since 2005, the exposome approach has been used to study the various factors that affect cancer risk, Caleb Finch, emeritus professor of gerontology at USC Leonard Davis, who wasn’t involved in the study, told Being Patient. In 2019, Finch was the first to propose that the exposome was important for understanding Alzheimer’s risk, especially how genetic factors interact with the environment. He believes this research lays the foundation for future large-scale studies looking at these interactions.  

“The prominent finding is that women are more at risk than men globally, but the particular factors [responsible for this disparity] may vary from place to place,” said Finch. 

Women, who are two times more likely than men to develop Alzheimer’s, might be more vulnerable to the risk factors that make the brain less resilient. “Factors such as gender inequality and adverse social conditions were more strongly associated with accelerated aging in women,” Hernández said.

A public health approach to improving brain health

Though the exposome might explain why someone experiences faster brain aging, it doesn’t necessarily explain why someone who’s otherwise healthy might develop dementia. “It’s the total package of factors in the environment,” Hernández said. “These are associations that increase risk” of various conditions, and may make the body and brain vulnerable to them without directly causing them. 

While previous research shows that many individual lifestyle factors, like diet and exercise, influence brain health and dementia risk, the impact of the exposome suggests that structural interventions are needed too. 

While some of these interventions, like reducing air pollution, adding more green spaces, and including healthcare access, are commonly discussed as means for Alzheimer’s and dementia prevention, Hernández highlighted some new priorities as well: decreasing economic inequality and strengthening democratic systems. 

“A key message is that brain health, traditionally attributed to personal choices, is not solely an individual responsibility,” he said.