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The effect of China's Clean Air Act on cognitive function in older adults: a population-based, quasi-experimental
Yao Yao1, Xiaozhen Lv1, Chengxuan Qiu1
1China Center for Health Development Studies (Y Yao MD), Center for Healthy Aging and Development Studies, Raissun Institute for Advanced Studies, National School of Development (Y Yao, Prof Y Zeng PhD), Dementia Care and Research Center, Clinical Research Division, Peking University Institute of Mental Health, Sixth Hospital (X Lv PhD, Prof H Wang MD), Beijing Dementia Key Lab, National Clinical Research Center for Mental Disorders, Peking University Sixth Hospital, National Health Commission Key Laboratory of Mental Health (X Lv, Prof H Wang), Institute of Reproductive and Child Health, Ministry of Health Key Laboratory of Reproductive Health and Department of Epidemiology and Biostatistics, School of Public Health (J Li MS, T Xue PhD), Peking University, Beijing, China; Aging Research Center, Department of Neurobiology, Care Sciences and Society, Karolinska Institutet-Stockholm University, Stockholm, Sweden (Prof C Qiu PhD); Stanford Data Science and Department of Statistics, Stanford University, Stanford, CA, USA (X Wu PhD); Department of Healthcare Policy and Research, Weill Cornell Medicine, New York, NY, USA (H Zhang PhD); Department of Health Policy and Management, University of Maryland School of Public Health, College Park, MD, USA (D Yue PhD); Public Health, Department of Social Medicine, Osaka University Graduate School of Medicine, Suita Shi, Osaka, Japan (K Liu PhD, E Salah Eshak PhD); School of Public Health, Peking University Health Science Center, Beijing, China (K Liu); Department of Public Health, Faculty of Medicine, Minia University, Minia, Egypt (E Salah Eshak); Department of Cardiology, University Heart and Vascular Center Hamburg, Hamburg, Germany (T Lorenz MA); Aging Futures Institute, The University of New South Wales, Sydney, NSW, Australia (Prof K J Anstey PhD); Division of Psychiatry, University College London, London, UK (Prof G Livingston MD); Global Health Institute and the Nicholas School of Environment (Prof J Zhang PhD), Center for the Study of Aging and Human Development and Geriatrics Division (Prof Y Zeng), Duke University, Durham, NC, USA.
Background:
Air pollution might accelerate cognitive ageing; it is unclear whether large-scale interventions, such as China's Clean Air Act (CCAA), can mitigate cognitive deterioration. We aimed to evaluate the effect of CCAA on changes in cognitive function in older adults.
Methods:
In this population-based, quasi-experimental study, we did a difference-in-differences analysis of the data collected during the 2014 and 2018 waves of the Chinese Longitudinal Healthy Longevity Survey (CLHLS). The study design used a counterfactual analysis feature by dividing CLHLS participants into two groups. The intervention group included participants who lived in areas where the provincial government set a target of reducing particulate matter (PM) by at least 5% annually from 2014 onward, whereas the control group consisted of individuals who lived in areas without a PM reduction target. Global cognitive function was measured using the Mini-Mental State Examination (MMSE). We used fixed-effects models to examine the between-group differences in MMSE score changes before and after CCAA implementation. We associated longitudinal changes in MMSE scores with changes in concentrations of PM with a diameter of less than 2·5 μm (PM2·5) concentration and other regulated pollutants. We used alternative models and sensitivity analyses to evaluate the robustness of the results from the main models.
Findings:
2812 individuals participated in the 2014 and 2018 surveys (mean age 81·0 years [SD 9·3] in 2014; 1408 [50·1%] female and 1404 [49·9%] male). 2251 (80·0%) were included in the intervention group and 561 (20·0%) in the control group. After controlling for potential confounders, the intervention group had a significantly smaller decline in MMSE scores from 2014 to 2018 compared with the control group: the mean between-group difference was 2·45 points (95% CI 1·32-3·57). Interquartile increases in PM2·5 were associated with a significant MMSE score decline of 0·83 points (95% CI 0·24-1·42); similarly, increases in SO2 were also associated with a significant MMSE score decline of 0·80 points (0·32-1·29).
Interpretation:
Implementing stringent clean air policies might mitigate the risk of air pollutant-associated cognitive ageing in older people.
Funding:
National Natural Sciences Foundation of China, National Key R&D Program of China, China Postdoctoral Science Foundation funded project, the Duke/Duke-National University of Singapore Collaboration Pilot Project, the National Institute on Aging and Peking University-Baidu Fund, Energy Foundation, and the Fundamental Research Funds for the Central Universities.
