What you need to know
- A statistical analysis has found associations between exposure to air pollution and declining cognitive performance.
- Air pollution includes exposure to airborne substances such as nitrogen dioxide and fine particulate matter.
- Cutting air pollution could have several health benefits.
British studies have shed light on the health consequences of exposure to air pollution and the benefits of reducing airborne toxins.
Air pollution is a global problem that has been shown to cause a range of health and environmental issues and is linked to increased rates of cancer, as well as heart, lung and reproductive problems. Research has connected it to 1.5 million deaths annually.
Contaminated air can also exacerbate existing health issues.
In 2020, an inquest listed air pollution as the cause of death for a 9-year-old girl with asthma in Southeast London.
Pollutants may also drive declining brain health.
One recently published study led by researchers from University College London has found a link between exposure to two common pollutants and below-average cognition among older Britons.
Among these toxins is nitrogen dioxide (NO2), a gas released by petrol-powered vehicles, industrial processes and fossil fuel burning.
The other is fine particulate matter — also known as PM2.5 — a cover-all term used to describe many substances released by burning processes that are less than 2.5 micrometers wide, about the size of many bacterial cells such as E.coli.
When controlling for geographic location and socioeconomic factors, the researchers found that the amount of ambient air pollution where a person lives is associated with lower levels of overall and executive brain function.
Though associations such as these do not strictly mean that higher air pollution causes lower brain function, the researchers are confident it would be proved by a more in-depth study.
Their confidence draws from the large dataset used for the research, known as the English Longitudinal Study of Ageing, which consists of almost a quarter century of data on people older than 50.
“We looked at the ongoing exposure, and we also knew the levels of cognitive function before. So we cannot be certain, but we’re pretty confident that there is not just an association [between exposure and cognition],” said Paola Zaninotto, a medical and social statistician at UCL.
Early study to shine light on brain impact
Zaninotto said the study was simply a first step toward finding a more definitive cause and effect. However, her multidisciplinary research group has drawn some initial conclusions from the study.
Cognitive decline could result from pollutants in the bloodstream affecting the areas of the temporal lobe, the section of the brain that processes sensory information, language, memory and emotions.
Research by other UCL medical specialists also found that NO2 and particulates hurt the functioning of the central nervous and circulatory systems.
“The exposure really is contributing to increase the cognitive decline and that in time will lead to dementia, so we really need to start thinking about reversing this trend,” Zaninotto said.
It is not an easy trend to reverse. Even those with the lowest exposures to ambient pollution were still subject to levels above limits recommended by World Health Organization guidelines.
These set a limit of 5 micrograms per cubic meter. The minimum exposure in the English cohort was eight and though reductions have been observed since the start of the study in 2010, some groups were exposed to levels nearly three times the recommendation as recently as 2017.
“There are improvements, but, despite these improvements, I think we are really still a long way from protecting people’s brain health,” Zaninotto said.
London transport measures show a way forward
If transport pollution is a major source of ambient air pollution, some policy measures may show a path to at least easing the concentration of contaminants.
An analysis by a pair of UK-based economists found that policies introduced in London to create “low emission zones” have been effective at cutting pollution.
The result has been an improvement in several health-related economic factors.
Low (LEZ) and Ultra Low Emission Zone (ULEZ) policies introduced for central London in the past two decades were credited with reducing NO2 levels by 21%, while coarse particulates were cut by 15%.
This led to improvements in the number of Londoners taking sick leave, and a 10% cut to respiratory problems.
ULEZ is one of the strictest emission regulations in the world, but other nations, including several in Europe, as well as major Asian capitals such as Beijing, Hong Kong, Tokyo and Hanoi, have introduced similar controls on vehicle emissions.
Though vehicles aren’t the only sources of air pollution, they are major drivers close to where people live and work.
Study co-author Eleonora Fichera, an applied economist at the UK’s University of Bath, said the connection between health outcomes and economic benefits wasn’t surprising.
“But the size of the effect is quite striking,” Fichera said.
In total, Fichera’s study attributed £37 million (€43.4 million) in annual savings to the combined benefits of the policies.
“[Low emissions zones] are a very quick way to bring down pollution and it has short-term effects and long-term effects,” Fichera said.
“We find reductions in particulate matter and nitrogen dioxide translate into productivity improvements, well-being and the mechanisms potentially [lead to] improvements in physical health,” she said.
Edited by: M. Gagnon
Sources
“And Breathe Normally”: Impacts of low emission zones on sick leave and mental well-being
Cognitive Performance and Long-term Exposure to Outdoor Air Pollution: Findings From the Harmonized Cognitive Assessment Protocol Substudy of the English Longitudinal Study of Ageing (ELSA-HCAP)
