Air pollution can cause harm to a person’s cognitive intelligence and increase the risk of diseases such as dementia, a new study suggests. 

Over the course of four years, scientists analysed the maths and verbal skills of around 20,000 people in China. They analysed these figures alongside data detailing levels of nitrogen dioxide and sulphur dioxide pollution near participants’ homes. 

They found the more exposed people were to polluted air, the greater their cognitive decline was over time. 

World Health Organisation figures from 2016 reveal that a staggering 92% of the world’s population are living in areas that exceed its own guidelines on air quality. Around 6.5 million deaths per year (11.6% of all global deaths) are associated with air pollution. 

In the latest study, researchers asked people aged 10 and above a set of standardised maths and word-based questions, each year from 2010 to 2014. Overall, exposure to air pollution was linked to cognitive decline, however, more research is needed to determine why this is the case and what pollutants are most to blame. 

The latest study suggests men are more affected by air pollution than women in terms of brain function, and the impact is greater the older a person is and the lower their education level. 

“We provide evidence that the effect of air pollution on verbal tests becomes more pronounced as people age, especially for men and the less educated,” the study, published in the journal Proceedings of the National Academy of Sciences, says.

“The damage on the ageing brain by air pollution likely imposes substantial health and economic costs, considering that cognitive functioning is critical for the elderly for both running daily errands and making high-stake decisions.”