Independent and combined relationships between light at night, air pollutants, PM components and risk of cardiovascular-kidney-metabolic syndrome: a cohort study.

BACKGROUND

Cardiovascular-kidney-metabolic (CKM) syndrome, characterized by interconnected cardiovascular, renal, and metabolic dysfunctions, poses a growing global health burden. While both light at night (LAN) and air pollutants have independently been linked to adverse health outcomes, their synergistic and joint effects on CKM syndrome risk remain poorly understood. This study aimed to assess the independent, interactive, and joint associations of LAN, air pollutants, and PM components with CKM syndrome.

METHODS

Data from 4,361 participants aged ≥ 45 years in the China Health and Retirement Longitudinal Study (CHARLS, 2011-2015) were analyzed. Cox proportional hazards regression models were employed to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for CKM syndrome risk. Multiplicative and additive interactions between LAN and air pollutants were assessed using likelihood ratio tests and relative excess risk due to interaction (RERI). Joint effects were evaluated by categorizing exposures into tertiles.

RESULTS

Over a median follow-up of 4.2 years, 792 incident CKM syndrome cases were identified. Adjusted models indicated that higher LAN exposure (highest vs. lowest quartile: HR = 1.46, 95% CI: 1.18-1.80) and increased levels of NO₂ (HR = 1.44, 95% CI: 1.18-1.75), PM (HR = 1.49, 95% CI: 1.19-1.87), PM (HR = 1.75, 95% CI: 1.40-2.18), NO₃⁻ (HR = 1.42, 95% CI: 1.15-1.75), and NH₄⁺ (HR = 1.42, 95% CI: 1.15-1.75) were independently associated with elevated CKM risk. Significant multiplicative interactions were observed between LAN and all pollutants except O₃, NO₃⁻, and NH₄⁺ (P for interaction < 0.05). In the additive interaction analysis, the RERI values ranged from 0.158 to 0.792, indicating a significant synergistic effect between LAN and air pollutants, which increases the risk of CKM syndrome. Joint exposure analysis showed that the combination of high LAN and high PM₁₀ increased CKM risk by 56.3% (HR = 1.563, 95% CI: 1.092-2.238), while moderate co-exposure to LAN and PM elevated risk by 33.4% (HR = 1.334, 95% CI: 0.872-2.041).

CONCLUSION

This study provided evidence that LAN, air pollutants, and PM components were positively associated with CKM syndrome, and significant synergistic and joint effects existed, increasing the risk of CKM syndrome in older adults. These results highlighted the urgency of comprehensive environmental intervention measures and emphasized the necessity of incorporating multi-factor joint exposure assessment in future CKM syndrome research.