Short-term association between ambient air pollution and heart rate variability: Unexpected findings from the population-based KORA S4 and FF4 studies
Objective: This study investigates the associations between short-term exposure to particulate matter (PM2.5), nitrogen dioxide (NO2), and heart rate variability (HRV) indices, including SDNN, RMSSD, pNN50, LF, HF, LF/HF ratio, and heart rate (HR), across two waves of the KORA study conducted 14 years apart. Additionally, the study explores effect modification by individual characteristics, including age, smoking status, and medication use.
Material and Methods: Data from 4,032 participants in KORA S4 (1999–2001) and 1,912 participants in KORA FF4 (2013–2014) were analyzed. Air pollution data were obtained from fixed monitoring stations. HRV indices were derived from 5-minute electrocardiogram recordings. Generalized additive models were applied to assess short-term associations of air pollution with HRV and HR. Effect modification by age, smoking status, and other individual characteristics was explored using interaction terms.
Results: In KORA S4, each IQR increase in 14-day moving average PM2.5 was associated with a -2.32% (95% CI: -4.41, -0.19) decrease in SDNN and a -0.74% (95% CI: -1.34, -0.13) decrease in pNN50. An IQR increase 14-day moving average NO2 was associated with a HR increase of 1.2% (95% CI: 0.16, 2.26). By contrast, KORA FF4 showed the opposite results with positive associations for all HRV indices (SDNN, pNN50, RMSSD, HF, LF) for both pollutants. Effect modification by age and smoking status showed smaller HRV responses for older smokers.
Conclusion: Short-term exposure to PM2.5 and NO2 impacts cardiac autonomic function negatively, with delayed effects being observed. However, the direction of the associations differed between the two study waves, potentially due to aging, smoking, medication use, and lower pollution levels in FF4 (29.87% lower PM2.5; 24.66% lower NO2). These findings highlight the importance of reducing air pollution exposure and considering individual susceptibility factors in cardiovascular risk assessments.