Air pollution has damaging effects on human cognitive ability, according to new research published in the journal Psychological and Cognitive Science.
Air pollution is a combination of fine particles and harmful ozone gas released by residential, commercial, and industrial combustion of coal and other fossil fuels.
According to a 2018 report from the Health Effects Institute, nearly 95% of the world's population currently lives in areas with air pollution that exceeds global air quality guidelines.
India, Pakistan, Qatar and Saudi Arabia all suffer from extreme amounts of air pollution and the burden of this pollution has already been shown to have significant effects on human health.
Research has shown that people who live in areas with polluted air are more likely to die from heart and lung disease, strokes and lung cancer compared with people who live in less polluted areas.
Studies have previously shown the effect that air pollution has on the brains of children and young adults, with inflammation of the brain tissue and disruption of the blood-brain barrier both being consequences of long-term polluted air exposure.
However, the Psychological and Cognitive Science article is the first to look at these effects across an entire population.
Looking at data from nationwide cognitive tests in China that include verbal and maths questions, the team of international researchers matched those scores for over 31,000 individuals with air quality data from 2010 to 2014 and found that polluted air impairs cognitive ability as people age.
Controlling for the expected effects of ageing, the researchers found that air pollution appears to impair scores on verbal tests and these effects become stronger as people age, particularly for men.
Xin Zhang, a researcher from the School of Statistics at Beijing Normal University and one of the study's co-authors, told BuzzFeed News that the team was surprised to find such a persistent effect on cognitive health.
"The damage on cognitive ability likely impedes the development of human capital. It is so widespread that [it] can impose substantial costs to everyone's daily life and critical decision-making."
The current annual cost of dementia is about US$818 billion. Zhang believes governments need to pay closer attention to air pollution: "Investment in cleaning up air pollution is not only good for health, but also for the intellect of society at large."