Long-term exposure to high levels of air pollution may harm the brain health of older adults in England, finds a new study led by UCL researchers.
The research, published in The Journals of Gerontology: Series A, found that exposure to nitrogen dioxide (NO₂) and fine particulate matter (PM2.5) is linked to lower scores in key cognitive abilities, particularly language skills.
NO₂ mainly enters the atmosphere through fuel combustion, originating from emissions of vehicles like cars, trucks, and buses, as well as power plants and off-road machinery. PM2.5 pollution in outdoor air often originates from the combustion of gasoline, oil, diesel fuel, or wood, and consists of tiny particles that can be inhaled deeply into the lungs.
The researchers analysed data from 1,127 adults aged 65 and over who took part in the ELSA Harmonised Cognitive Assessment Protocol (ELSA-HCAP) in 2018.
The team examined exposure to air pollution over an eight to 10 year period (2008-2017) and assessed participants' memory, executive function (i.e. making plans, solving problems and adapting to new situations), language, and overall cognitive function.
Participants completed a range of well-established neurocognitive memory assessments such as the "East Boston Memory Test" and the "Wechsler Memory Scale", alongside immediate and delayed recall, backwards counting tasks, and shape drawing.
The findings showed that individuals residing in areas with the highest levels of NO₂ and PM2.5 performed worse on cognitive tests compared to those living in areas with average pollution levels. The most compelling evidence of association was observed in language skills, with individuals in the most polluted areas scoring in the bottom third of the cognitive tests performed.
The study also found that different sources of air pollution have varying effects on cognitive health. For example, pollution from industries, home heating, and combustion of fuels (like coal and oil) were strongly linked to poorer language performance (i.e. the ability to access and produce words quickly).
The authors did not examine the reasons behind their findings but suggest that this may be because increased air pollution exposure is most strongly associated with impairment in the temporal lobe (the part of the brain which is essential for language and semantic fluency). Further research is needed to understand these links.
Lead author Dr Giorgio Di Gessa (UCL Epidemiology & Health) said: "Our study shows that air pollution is not just harmful to the lungs and heart but also to brain health, especially when people are exposed to high levels for long periods.
"The most consistent links we found were with language ability, which may indicate that certain pollutants have a specific effect on particular cognitive processes."
Consequently, the researchers urge policymakers to strengthen air quality regulations, particularly in areas where pollution levels remain high, to help protect brain health as the population ages.
Deputy director of the ELSA study, Professor Paola Zaninotto (UCL Epidemiology & Health), said: "By tracking pollution levels over a decade using high-quality data, our research provides robust evidence that sustained exposure to pollutants is damaging people's brains."
ELSA is funded by the National Institute on Aging and by UK Government Departments coordinated by the National Institute for Health and Care Research (NIHR).
Study limitations
The air pollution data used in the study only covers 10 years, which may not accurately represent lifetime exposure.
Meanwhile, yearly averages of pollution levels were used, missing short-term high exposure impacts.
Additionally, the study sample is small and limited to England, which may not reflect broader trends.
