Air pollution has countless victims—nearly nine out of ten people across the globe breathe polluted air, according to the World Health Organization – and new research from London suggests it even reaches the unborn, moving from a mothers’ lungs to placenta and foetus.
While the toll breathing polluted air exacts on health and physical well-being is well documented and well-known, lesser known is its impact on human intelligence.
In the first study of its kind, we found continued exposure to air pollution lowers human intelligence, with the effects becoming more pronounced with age. The research was conducted with colleagues Xin Zhang of Beijing Normal University, and Xi Chen of Yale School of public Health.
In developing countries, which top the list of world’s most polluted cities, this translates into not only significant health and economic costs, but also human development costs.
India, home to six of the top ten polluted cities in the world, has struggled in recent years to curb pollution in its capital city, New Delhi, and neighboring states. Every year, the air pollution worsens during late fall and early winter, coinciding with the crop burning season, and turning it into a more permanent rather than a transient feature of city life.
The situation is similar in Zabol (Iran), Gwalior (India), Allahabad (India), Riyadh (Saudi Arabia), Al Jubail (Saudi Arabia), Patna (India), Raipur (India), Bamenda (Cameroon), Xingtai (China) and Baoding (China), which have at least 12 times the number of air pollutants than in the least polluted country, New Zealand.
The quality of life in some of the world’s busiest cities and hubs of rapid economic growth has been hijacked by air pollution, and its residents are unwillingly and unconsciously becoming afflicted by disease.
But, even at that rate, the damage may be more severe than what the city dwellers had bargained for. Our research, conducted in China, which has long struggled with extreme levels and extended bouts of air pollution, studied the link between air pollution and its impact on human intelligence. With a sample size of nearly 32,000, we examined the relationship between computerised verbal and math test scores, taken from the nationally representative China Family Panel Studies longitudinal survey conducted in 2010 and 2014, with short- and long-term air pollution exposure calculated from official air pollution index values.
Both verbal and math scores decreased with increasing cumulative air pollution exposure, with a steeper decline for verbal scores than math scores. The decline in verbal scores was more pronounced among males than females. Among males, the decline in verbal scores became more pronounced with age, and this age dependence was greater in those with less than a middle school education compared with a middle school education or more.
The damage air pollution has on aging brains imposes substantial health and economic costs, considering that cognitive functioning is critical for the elderly to both running daily errands and making high-stakes economic decisions. This finding has been neglected thus far in the policy discourse and holds important policy implications. Cognitive decline or impairment are, needless to add, risk factors of Alzheimer’s disease and other forms of dementia for the elderly.
Any efforts to reverse the rising air pollution bring considerable benefits including for cognitive abilities. We found reduction of fine particulate matter concentrations that indicate air pollution to the U.S. Environmental Protection Agency (EPA) standard (50 μg/m3) will significantly increase verbal and math scores: 12 unit decrease in pollution on the Air Quality Index leads to one-year education gain for older men (age 65 and more), who received schooling for up to 6 years.
These research findings on China shine light on other developing countries as well, which are undergoing rapid economic transformation, and witnessing high rates of urbanization, exerting unprecedented strain on existing resources. WHO says world’s top 20 most polluted cities are in developing countries, and almost all the cities in low- and middle-income countries with more than 100,000 residents fail to meet its air quality guidelines.
However, it’s not only the developed countries which have to worry about air pollution. Efforts to safeguard environment and reduce air pollution received a serious setback when in August 2018, the Trump administration announced plans to dramatically relax fuel efficiency standards, a move likely to flood American communities with dangerous airborne particulates from vehicles. Reports suggest that EPA determined that Trump’s new regulations for emissions at coal-burning power plants will cause an additional 1,400 deaths a year.
Amid such policy reverses and setbacks, remedying the current situation in the worst affected countries requires sustained political will and evidence-based policy measures, which even if implemented now are unfortunately at least a decade too late. New evidence about the negative impact pollution has on mental health compounds the evidence that hazardous pollution across the developing world has serious deleterious consequences for millions of lives, and policymakers need to find ways to clean up pollution, take lessons from countries which have made considerable progress to bring it down, or everyone will suffer serious health consequences and costs down the road.
Xiaobo Zhang is a senior research fellow at the International Food Policy Research Institute and professor of economics in the National School of Development at Peking University.
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