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Chronic exposure to air pollution could be linked to cognitive performance, the negative impact increases with age, and affects men with less education that do manual job outdoors for long hours. Over four years, the maths and verbal skills of some 20,000 people in China were monitored by the US-Chinese study.
Researchers believe the results have global relevance, with more than 80% of the world’s urban population breathing unsafe levels of air pollution. However, while establishing a link between pollution and lower test scores, the study did not prove cause and effect.
The study was based on measurements of sulphur dioxide, nitrogen dioxide and particulates smaller than 10 micrometres in diameter where participants lived. Carbon monoxide, ozone and larger particulates were not included in the study. Air pollution causes an estimated seven million premature deaths a year worldwide, according to the World Health Organization.
The effect of air pollution on verbal tests becomes more pronounced as people age, pollution also increases the risk of degenerative diseases such as Alzheimer’s and other forms of dementia. In this study, researchers tested people of both sexes aged 10 and above between 2010 and 2014, with 24 standardised maths questions and 34 word-recognition questions.
Previous studies found air pollution had a negative impact on students’ cognitive abilities. Many pollutants are thought to directly affect brain chemistry in a variety of ways – for instance, particulate matter can carry toxins through small passageways and directly enter the brain.
Some pollutants can also have a psychological impact, increasing the risk of depression. About seven million people die every year from exposure to polluted air, Air pollution caused 4.2 million deaths globally in 2016, 91% of the world’s population lives in places where air quality exceeds WHO guideline limits.