Air pollution lowers brain function, can lead to lower verbal and maths scores

Long-term exposure to air pollution lowers brain function, which reflects in decreased verbal and mathematics scores, apart from causing heart disease and breathing problems, a new study from China has said.

“... a narrow focus on the negative effect on health may underestimate the total cost of air pollution. Our findings imply that the indirect effect of pollution on social welfare could be much larger than previously thought,” Xiaobo Zhang, one of the authors of the paper, said.

The study retrospectively analysed data of nearly 32,000 people from two waves (2010 and 2014) of the China Family Panel Study, a nationally representative longitudinal survey that looks at topics like economic activities, education outcome, family dynamics, relationships, and health.

The cognitive ability module of the test has standardised mathematics and word-recognition questions and was sorted in ascending order of difficulty. The score given was the highest rank of a question that a person was able to answer. This dataset was then compared to the local pollution data.

The researchers were able to show that the scores of the cognitive module of the test fell with increased long-term and transient exposure to air pollution. The decline was more pronounced in the verbal tests than in mathematics.

When the results were plotted based on gender and educational qualification, the researchers saw that men 44 years or older with primary school education were the most impacted. For subsample with more education, men 65 years and above were impacted.

“We speculate that the pollutant damage is most likely accumulating in the white matter of the brain which is mainly associated with the language functioning. The negative impact of three-year accumulative exposure to air pollution for men’s verbal test scores is 49% higher than that for women,” Zhang, who is also a senior research fellow with the Washington-based International Food Policy Research Institute (IFPRI), said.

“This could be because men have a much smaller amount of white matter activated during intelligence tests so their cognitive performance is more affected. Of course, more research is needed to test this out,” Zhang added.

The research estimated that reducing fine particulate matter concentrations to the US Environmental Protection Agency (EPA) standard (50 μg/m3) would increase verbal and math scores by 2.41 and 0.39 points.

Though the research was conducted in China, the researchers suggest that the implications would be true for all developing countries, including India.

The world’s top 20 most polluted cities, according to the World Health Organization’s (WHO) database, are in developing countries. Almost all the cities in low- and middle-income countries with more than 1,00,000 residents fail to meet WHO air quality guidelines.

“The findings should be applicable to India. In fact, the impact probably is greater given that the air pollution is more severe in Delhi than in Beijing and other Chinese cities,” said Zhang.

Doctors from India said the study was a good start but added that more research is required to show that the impact of air pollution on the human brain is definitive.

“The study points a way. However, the researchers have retrospectively analysed the data and tried to fit it into a mathematical model. This can just show a correlation between high pollution levels and lower scores,” Dr Vinay Goyal, professor of neurology at All India Institute of Medical Sciences (AIIMS), said.

“Also, what about the socio-economic parameters? Most likely than not the people living in the most polluted areas are the poorest, they might not fare well on the test, not because of pollution but also because of the missing opportunities,” Dr Goyal, who is also the editor of the journal Annals of Indian Academy of Neurology, added.

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