Synergistic impact of air pollution and artificial light at night on memory disorders: a nationwide cohort analysis

Air pollutants and outdoor artificial light at night (ALAN) are known health risks, with established effects on respiratory and cardiovascular health. However, their impact on cognitive function, particularly neurodegenerative diseases like Alzheimer's, remains poorly understood.

Using data from the China Health and Retirement Longitudinal Study (CHARLS) and the China Family Panel Studies (CFPS), including 44,689 participants, memory impairment (Memrye) was defined by self-reported memory-related diseases. Cox regression models were applied to assess the relationship between pollutants, ALAN exposure, and Memrye. Interaction analyses evaluated the combined effects using relative excess risk due to interaction (RERI), attributable proportion (AP), and synergy index (S). Biomarker analyses and stepwise causal mediation examined the underlying mechanisms.

Air pollutants and ALAN were significantly associated with Memrye (p < 0.05), with hazard ratios (HR) ranging from 1.010 to 1.343. Synergistic effects were observed, such as for PM2.5 and ALAN, with RERI, AP, and S values of 0.65 (0.33, 0.97), 0.30 (0.26, 0.34), and 1.43 (1.21, 1.65), respectively. Biomarker analyses showed significant correlations between pollutants, glucose, cholesterol, and uric acid, while ALAN was negatively associated with glucose and uric acid. Mediation analyses indicated that PM_2.5, NO₂, and ALAN indirectly affected Memrye through biomarkers, accounting for 1.07-8.28% of the total effects.

Air pollution and ALAN exposure are linked to memory impairment, with combined effects potentially amplifying risk. Biomarkers play a key role in mediating these effects, suggesting a need for targeted public health measures to mitigate these environmental health risks.