Air pollution is already known to cause 4.5 million deaths a year, and a wide range of illnesses, but it has a more insidious effect as well. The greater your exposure to air pollution, the worse your scores will be on verbal and math tests, indicating a decline in cognitive capacity. The findings suggest that, among many other things, exposure to pollution makes it harder for people to find solutions to problems – including presumably the problem of air pollution.
Studies on the effects of air pollution on cognitive performance have been conducted on young students, but this may not be the most relevant aspect to consider, a paper in Proceedings of the National Academy of Science notes. The rare efforts to assess the effects on the brain of exposure to bad air for a wider population have struggled to take into account other variables that might be distorting the results.
Dr Xin Zhang of Beijing Normal University and co-authors compared test scores from a study run on a representative sample of Chinese families with air pollution in their home city on the day of the test and over longer periods. They found an association between pollution exposure and large declines on verbal and tests and smaller ones for mathematics.
“The effect of air pollution on verbal tests becomes more pronounced as people age, especially for men and the less educated,” the authors concluded. For example, for men with only primary school education, exposure to air pollution was associated with a significantly greater decline in verbal skills from age 44, whereas for more highly educated men the effect appeared after 65.
The authors argue their conclusions are probably relevant for any location with high ongoing levels of air pollution – something that includes 98 percent of cities in low and middle-income countries with populations over 100,000.
The consequences at both an individual level, and for society, are staggering. Cognitive decline is a risk factor for dementia and has a serious impact on quality of life. The economic consequences for people who are less able to take care of themselves or make important decisions are hard to calculate, but certainly enormous.
Air quality for the study was based on measurements of sulfur dioxide, nitrogen dioxide, and particulates smaller than 10 micrometers in diameter at the locations where participants lived. Whether one of these pollutants is more to blame for the negative effects than the others is not known.
Poorer people and ethnic minorities are frequently exposed to much higher levels of air pollution than more privileged counterparts, reflecting differences by neighborhood. That’s something to remember, the next time you hear the (increasingly frequent) claims differences in IQ scores between populations are genetic, rather than environmental.