The research tried to minimize the impact of other variables besides pollution. For example, it excluded test takers who migrated across counties between 2010 and 2014, and others who worked in mining, smelting, wood processing and other “polluted occupations.”
However, Dr. He said, measuring long-term effects of pollution exposure can be difficult, in part because individual exposure depends on so many factors — including, for example, whether a person uses air filters at home.
In another critique, Rajasekhar Balasubramanian, an air quality expert at the National University of Singapore, noted that while the study’s authors speculate that continued exposure to pollution can alter brain chemistry, they offered no clinical proof. (The authors agreed, writing that the hypothesis should be explored further.)
But Dr. Balasubramanian said the study was useful in part because, while the effects of pollution on children’s cognition had been documented by epidemiologists, this was the first to focus on such risks to China’s older people. He said similar research was now needed in other countries.
“The outcome of such studies would provide a sound scientific basis for tightening air quality standards to curtail air pollution and protect public health in both developing and developed countries,” Dr. Balasubramanian, who was not involved in the study, said in an emailed statement.
As public outrage has grown in China over smog and respiratory illnesses related to it, officials have in recent years closed hundreds of coal-fired power plants, imposed limits on driving and residential coal burning, and sent teams of police officers to inspect factories.
But China’s carbon dioxide emissions increased last year, and even though the country is on its way to meeting its major climate change goals, many of its cities still have dangerously high levels of outdoor air pollution.
In one sign of the problems, a study published in April found that about 142 million people, or just over half the population surveyed in 155 Chinese cities, were exposed in 2014 to average annual “multicontaminant concentrations” that were above the World Health Organization’s limits. The study said that eastern China and megacities were worst affected.