Temperature- and humidity-modified associations between ambient air pollution and syncope outpatient visits: a time series analysis in Beijing, China

Atmospheric factors, particularly air pollution, may act as potential triggers for syncope. In this study, we explored the associations between exposure to air pollution and syncope outpatient visits. Data from syncope outpatients at Beijing Tiantan Hospital between 2014 and 2018, daily average levels of air pollutants, such as particulate matter ≤ 2.5 μm and ≤ 10 μm in diameter (PM2.5 and PM10), nitrogen dioxide (NO2), and sulfur dioxide (SO2), along with meteorological factors (temperature and relative humidity (RH)) during the same timeframe, were used to construct the datasets. A time-series study employing a Poisson regression model was conducted to investigate the impact of air pollutants on syncope outpatients. The potential modifying effects of minimum temperature (Temp-Min) and RH were further evaluated by stratifying into four quartiles: low, middle-low, middle-high, and high. The results revealed a significant association between air pollution and syncope risk. Specifically, a 10 µg/m3 increase in PM2.5, PM10, and NO2 was associated with significant increases in syncope outpatients, with the risk increasing by 0.41% (95% confidence interval (CI): 0.00%, 0.82%), 0.27% (95% CI: -0.03%, 0.56%), and 1.27% (95% CI: 0.18%, 2.37%), respectively. Subgroup analyses revealed stronger associations in males and older adults (71–80 years) than in females and other age groups. Moreover, lower temperatures (< 9.8 °C) and moderate RHs (25 ~ 50th percentile) aggravated the effects of air pollution on syncope outpatients (P < 0.05). This study revealed that the risk of syncope is increased by short-term exposure to air pollution and that this effect is exacerbated by temperature and RH.