While health has long been thought the most common casualty of air pollution, a landmark study from an International Food Policy Research Institute (IFPRI) researcher establishes for the first time that exposure to air pollution over a long period significantly impacts cognitive abilities, as measured through steep reduction in verbal and math tests scores.
“Long-term exposure to air pollution impedes cognitive performance in verbal and math tests,” said study author Xiaobo Zhang, senior research fellow at IFPRI and distinguished chairman-professor of economics at Peking University.
“The damage on cognitive ability by air pollution also likely impedes the development of human capital. Therefore, a narrow focus on the negative effect on health may underestimate the total cost of air pollution,” Zhang added.
“Our findings on the damaging effect of air pollution on cognition imply that the indirect effect of pollution on social welfare could be much larger than previously thought.”
The study was held in China in 2010 and 2014.
It noted that air pollution is a ubiquitous problem in developing countries. It cited the global ambient air pollution database compiled by the World Health Organization, which said that the top 20 most polluted cities are all in developing countries. The WHO said that almost all of the cities (98 percent) in low and middle-income countries with more than 100,000 residents fail to meet WHO air quality guidelines.
“Therefore, the research findings on China, the largest developing country with severe air-pollution, can also shed light on other developing countries,” the study said. The report includes 86 major cities in China in 2000 and covers most of the country’s cities in 2014.
In the Philippines—among the polluted in developing countries—the average particulate matter (PM) 2.5 concentration in early-2018 is 21 microgram (µm) per cubic meter annually, which is twice over the recommended value, news reports said.
In the study, air quality was measured using the air-pollution index, which is calculated based on daily readings of three air pollutants, namely sulfur dioxide, nitrogen dioxide and PM smaller than 10 µm (PM10). The API ranges from 0 to 500, with larger values indicating worse air quality, the study said.
While the health consequences of air pollution are well known, few studies have examined its impact on cognitive abilities. The study, “The impact of exposure to air pollution on cognitive performance,” coauthored by IFPRI’s Zhang, Xin Zhang of Beijing Normal University and Xi Chen of Yale University, was published in the latest issue of the journal, Proceedings of the National Academy of Sciences.
The study, with a sample size of nearly 32,000, examined the relationship between cognitive 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 API values. CFPS is a nationally representative survey of Chinese families and individuals.
Both verbal and math scores decreased with increasing cumulative air-pollution exposure, with a steeper decline for verbal scores than math scores, according to the key findings of the study.
The decline in verbal scores was more pronounced among males than females, the study said. 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 likely imposes substantial health and economic cost, 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 in the policy discourse, and has important policy implications,” Zhang said.
Cognitive decline or impairment are risk factors of Alzheimer’s disease and other forms of dementia for the elderly.
As the most expensive form of cognitive decline, Alzheimer’s disease alone costs $226 billion of health services and 18 billion labor hours of unpaid caregiving in 2015, the study said.
The study noted that, given that senior citizens have to make a host of complex high-stake economic decisions—such as purchasing health insurance and planning retirement—the decay in cognitive ability induced by air pollution will likely impair the quality of the important decisions.
“Given that cognitive ability shapes human behavior and decision making, our result provides supporting evidence on the findings about the negative effect of air pollution on decision making, risk attitude and behavior. The damage on cognitive ability by air pollution also likely impedes the development of human capital,” the study said.
The research estimated that reducing fine particulate matter concentrations to the US Environmental Protection Agency standard (50 µg/m3) would increase verbal and math scores by 2.41 and 0.39 points, respectively, equivalent to an increase from the median to the 63rd and 58th percentiles, respectively.
“These research findings on China, the largest developing country with severe air pollution, also shed light on other developing countries,” Zhang said.
A previous study by the same author, Xiaobo Zhang, had documented the negative impact of air pollution on mental health and subjective well-being.
IFPRI is an international research center that seeks sustainable solutions for ending hunger and poverty. It was established in 1975 to identify and analyze alternative national and international strategies and policies for meeting the food needs of the developing world, with particular emphasis on low-income countries and on the poorer groups in those countries.