An international study published across 34 countries, including Ireland, shows that the biological age of the brain can be accelerated or delayed by environmental risk (air pollution, public housing conditions) and protective factors (socioeconomic equality, access to healthcare). The stronger effects arise from interactions among environmental, social, and political conditions. The paper was published recently in the journal Nature Medicine.
Using data from 18,701 individuals across 34 countries, the study shows that the exposome (the cumulative set of environmental, social, and sociopolitical exposures that individuals experience throughout life) operates in a syndemic manner — when two or more health problems occur together and interact in a way that makes each other worse — with multiple co-occurring exposures having very large effects, shaping brain ageing across both healthy individuals and those with neurodegenerative conditions.
The researchers quantified 73 different environmental factors measured at country level indicators spanning air pollution, climate variability, green space, water quality, socioeconomic inequality, and multiple indicators of political and democratic contexts. When modelled jointly, these factors explained up to 15 times more variance in brain ageing than any single exposure alone. This finding highlights a key shift: Environmental influences on brain health are cumulative and non-linear, with interactions across domains amplifying their biological impact.
Agusti?n Iba?n?ez, lead investigator and corresponding author, said: “We aimed to test whether the combined, syndemic effects of environmental exposures better explain variability in brain ageing across populations than individual exposures or single clinical diagnoses.”
The study identifies distinct but complementary brain markers. Combined physical exposures (increased pollution, extreme temperatures and lack of green spaces) were primarily associated with structural brain ageing, particularly affecting regions, central to memory, emotional regulation, and autonomic functions. These structural changes are consistent with mechanisms such as neuroinflammation, oxidative stress, and vascular dysfunction, all of which may contribute to tissue degeneration.
In contrast, social exposomes like poverty, inequality, and lack of support can strongly affect how the brain ages. These pressures are linked to faster ageing in brain areas responsible for thinking, emotions, and social behaviour. This may happen because the brain is constantly adapting to long-term stress. In fact, these combined social challenges can have an even bigger impact on brain aging than diseases like dementia and cognitive impairment. Overall, this effect is consistent across different brain measures, clinical groups, and long-term assessments.
The findings have important implications for prevention, public health, and policy. Current strategies to promote healthy brain aging often focus on individual behaviours (diet, exercise, or cognitive training) or on treating disease once symptoms emerge. While these approaches are critically important, they address only part of the risk landscape. Many drivers of brain ageing operate at broader structural levels, including environmental conditions, social inequalities, and institutional stability.
