Causal effects of prenatal and chronic PM_2.5 exposures on cognitive function

Growing evidence indicated an association between PM_2.5 exposure and cognitive function, but the causal effect and the cognitive effect of prenatal PM_2.5 exposure remain elusive. We obtained 15,099 subjects from a nationally representative sample of China and measured their cognitive performance. We ascertained subjects' prenatal PM_2.5 exposure and chronic PM_2.5 exposure of the recent two years. Using this national sample, we found that PM_2.5 exposure during the mid- to late-pregnancy was significantly associated with declined cognition and income; chronic PM_2.5 exposure was also independently associated with cognition and income measured at adulthood with greater magnitude. Negative effect modification was observed between prenatal and chronic PM_2.5 exposure. Instrumental variable approach and difference-in-difference study verified causal effects: every 1 μg/m³ increase in prenatal and chronic PM_2.5 exposures were causally associated with -0.22% (-0.38%, -0.06%) and -0.17% (-0.31%, -0.03%) changes in cognitive function, respectively. People with low cognition and low income were more vulnerable to PM_2.5 exposure with greater cognitive and income decline. In the future, although China's improved air quality continues to benefit people and reduce cognitive decline induced by chronic PM_2.5 exposure, high prenatal PM_2.5 exposure will continue to hurt the overall cognition of Chinese population, since in total 360 million people were born during the 2000-2020 polluted era. Prenatal PM_2.5-induced cognitive decline would remain largely unchanged before 2050 and gradually reduce after 2065, regardless of environmental policy scenarios. The long-lasting cognitive impact of PM_2.5 is worth considering while enacting environmental policies.