Exposure to air pollution in midlife may slow thinking and cause brain changes in later life, potentially affecting cognitive health as people age.
A 26-year study tracked 1,761 people aged 45 and over, assessing their exposure to air pollutants and testing their cognitive function at four points between ages 43 and 69.
Researchers from King’s College London’s Institute of Psychiatry, Psychology & Neuroscience (IoPPN), in collaboration with University College London, the University of Leicester and Alzheimer’s Research UK, found that those exposed to higher pollution levels from age 45 scored lower on cognitive screening tests at age 69.
The Addenbrooke’s Cognitive Examination, which assesses attention, memory, language, perception and verbal fluency, showed poorer results among those with greater exposure to air pollution. Participants exposed to high levels of nitrogen dioxide (NO₂) and particulate matter (PM₁₀) also demonstrated slower processing speeds between ages 43 and 69.
Brain scans from a subgroup of participants aged 69 to 71 revealed physical differences linked to pollution exposure. High exposure to nitrogen oxides (NOₓ) was associated with a smaller hippocampus – a brain region involved in memory. Greater exposure to NO₂ and PM₁₀ was linked to larger ventricular volume, which tends to increase when brain tissue reduces.
Both outcomes are associated with cognitive decline and dementia. These associations remained even after adjusting for childhood cognitive scores and pollution exposure before age 45. However, no clear link was found between air pollution and verbal memory alone.
“153 million people are predicted to be living with dementia by 2050. Our study represents one of the longest follow ups that seeks to understand the impact of air pollution on a broad range of cognitive outcomes and on brain health as we age. Most of the world’s population is breathing toxic air above World Health Organization recommended limits, which could partly explain the increased dementia risk as people age,” said Professor Ioannis Bakolis, deputy director at the Centre for Mental Health Policy and Evaluation at King’s IoPPN and the study’s principal investigator.
Thomas Canning, one of the study’s first authors from King’s IoPPN, added: “For some time, researchers have been seeking to highlight the long term and potentially permanent effects of air pollution on the brain. Our study highlights that reducing people’s exposure has the potential to help conserve cognition and brain structure as they age, even if this happens once they reach mid-life.”
The findings suggest that even small reductions in air pollution exposure during midlife could help preserve cognitive function and brain structure in later years. With most of the global population breathing air above World Health Organization limits, the results add to evidence linking air quality with long-term health outcomes.
The study was part-funded by the National Institute for Health and Care Research Maudsley Biomedical Research Centre, with further support from the Medical Research Council, Alzheimer’s Research UK, Alzheimer’s Association, MRC Dementias Platform UK, Wolfson Foundation and Brain Research UK.
