A new study led by researchers from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King's College London, has found that exposure to higher levels of air pollution during mid-life is associated with slower processing speed, lower scores on a cognitive screening tool, and differences in brain structure later in life.
Published in Lancet Healthy Longevity, the research was conducted in partnership with University College London (UCL), University of Leicester and Alzheimer's Research UK (ARUK). It provides further evidence that exposure to air pollution is linked with poorer brain health as humans age and suggests that even small reductions in levels of exposure could conserve cognition and brain structure in older people.
This research combined an analysis of health survey data with a neuroimaging sub-study to gain a more detailed understanding of the effects of exposure to a range of air pollutants.
Researchers examined the data available from 1,761 participants aged 45 and over who had taken part in the Medical Research Council's (MRC) National Survey of Health and Development (NSHD). The team examined modelled exposure to air pollution over a 26-year period and assessed participants' verbal memory and processing speed at ages 43, 53, 60-64, and 69. They also underwent an Addenbrooke's Cognitive Examination cognitive screening test at age 69, designed to detect cognitive impairment and dementia.
Researchers also analysed data from a substudy from NSHD - Insight 46 - in which a smaller group of NSHD participants aged 69 -71 year underwent a brain scan. Unlike previous work, this study could control for lifetime exposure to a range of pollutants while also adjusting for an extensive range of clinical and sociodemographic factors, including childhood cognition.
When analysing the data, researchers found that, at age 69, those participants who had been exposed to higher levels of all air pollutants from age 45 onwards had lower scores on their ACE III tests, which measures attention, memory, verbal fluency, language and perception. Those participants who were exposed to high levels of nitrogen dioxide (NO2) and particulate matter (PM10) also demonstrated slower processing speeds between the ages of 43 and 69. These associations remain significant even after accounting for participants' childhood cognitive ability and air pollution exposure up to age 45. The researchers did not, however, find any conclusive association between air pollution and verbal memory.
In the neuroimaging substudy, researchers found that high levels of exposure to NOX was associated with smaller hippocampal volume while increased levels of exposure to NO2 and PM10 was associated with larger ventricular volume, which increases in size when brain tissue reduces. Both brain structure outcomes are linked with cognitive impairment and dementia.
"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."
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 said, "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."
NSHD is funded by the Medical Research Council. Insight 46 is funded by Alzheimer's Research UK, Alzheimer's Association, MRC Dementias Platform UK, Wolfson Foundation, the MRC and Brain Research UK.
Associations between life course exposure to ambient air pollution with cognition and later-life brain structure: a population-based study of the 1946 British Birth Cohort (DOI10.1016/j.lanhl.2025.100724) (Canning, Bakolis et al) was published in Lancet Healthy Longevity.
