Air pollution has long been linked to cognitive decline, particularly in older adults. However, a new study has shed light on how various types of air pollution influence specific areas of cognitive function, offering new insights into this ongoing issue.
The research, published in The Journals of Gerontology, examines the impact of long-term exposure to different pollution sources on memory, language, and executive function. The study followed participants for nearly a decade to uncover the connections between air pollution and brain health.
Cognitive decline is a well-known aspect of aging, affecting the quality of life and life expectancy. Air pollution is estimated to contribute to 2.6% of dementia cases, surpassing more commonly recognized risk factors like high blood pressure or physical inactivity.
Among the pollutants most linked to cognitive impairment are nitrogen dioxide (NO₂) and fine particulate matter (PM2.5), both of which can negatively impact the brain and cardiovascular system through direct exposure and systemic effects. However, the sources of these pollutants vary, with different types of emissions potentially influencing cognitive outcomes in different ways.
For example, traffic-related pollution is often rich in black carbon and nitrates, while agricultural emissions typically contain higher levels of ammonium. This variation may explain differences in how pollution impacts brain health, with recent research in the U.S. showing that new dementia cases are most strongly associated with PM2.5 from agriculture and wildfires.
To explore these questions, the study used data from the 2018 Harmonized Cognitive Assessment Protocol (HCAP) as part of the English Longitudinal Study of Ageing (ELSA). Researchers looked at the average outdoor concentrations of NO₂, total PM2.5, and specific PM2.5 sources between 2008 and 2017. They then examined how these pollution levels affected memory, executive function, language, and overall cognitive function.
The study accounted for factors such as age, sex, socioeconomic status, urban or rural location, and educational background, but did not include pre-existing health conditions.
Findings
The participants, who had an average age of 65, were primarily from urban areas, with about a quarter in the highest socioeconomic group and 14% in the most deprived group. Between 2008 and 2017, exposure to NO₂ averaged 23 μg/m³, and from 2010 to 2017, PM2.5 levels averaged 12 μg/m³. Encouragingly, both pollutants showed a decline over this period, with NO₂ decreasing from 28 μg/m³ in 2008 to 21 μg/m³ in 2017, and PM2.5 dropping from 13.5 μg/m³ to 10.3 μg/m³.
The study found a clear pattern: higher pollution levels were linked to poorer cognitive scores, with the lowest global cognitive scores observed at the highest levels of NO₂ and total PM2.5, especially in residential areas. Memory and executive function also followed this pattern.
Interestingly, while overall cognitive function was not significantly affected by the source of emissions, language skills were notably impacted. Specifically, exposure to PM2.5 from industrial activities and residential fuel combustion, including biofuels, oil, natural gas, and coal, was consistently linked to poorer language performance.
These findings support previous research, although earlier studies had shown mixed results regarding the impact of pollution on specific cognitive domains. The new study’s identification of particular pollution sources, particularly industrial and residential combustion, as key contributors to language decline is significant. It suggests potential damage to the brain’s temporal lobe, which plays a key role in language processing.
This research adds to the growing body of evidence showing that air pollution can harm cognitive function, particularly in older adults. While general cognitive abilities, memory, and executive function were affected, the most significant impact was on language skills, especially from emissions linked to industrial and residential combustion sources.
A crucial takeaway from the study is that all participants were exposed to pollution levels exceeding the World Health Organization’s 2021 Air Quality Guidelines. This highlights the urgent need for stronger public health policies and environmental measures to reduce pollution, particularly in areas at high risk.
Efforts to address this issue could involve better urban planning, improved housing conditions, enhanced healthcare access, and stronger environmental monitoring systems to protect vulnerable populations from the harmful effects of air pollution.
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