Short-term effects of haze exposure on clinical and subclinical cardiovascular indicators among adults in Nanjing

Haze has remained a persistent environmental issue in Nanjing, exhibiting notable temporal variation. Emerging evidence suggests that haze weather contributes to elevated cardiovascular mortality, yet the underlying mechanisms remain unclear. We analyzed annual trends in haze days in Nanjing from 2005 to 2023 and found that the number of haze days decreased mainly during the warm season, while levels remained high during the cold season. Further, we analyzed 103,833 health examination records from local hospital (2019-2023) focusing on 12 cardiovascular indicators in relation to haze exposure. We employed a linear mixed effects model combined with a distributed lag nonlinear model to evaluate the associations. Stratified analyses were conducted based on demographic characteristics including sex, age, body mass index (BMI), diabetes and hypertension. Significant associations were observed for most cardiovascular indicators at lags 0-2 days, peaked at lags 3-5 days, and weakened at lags 6-7 days. Significant cumulative percentage changes were observed in several cardiovascular indicators over lag 0-7 days, including blood pressure (0.55%-1.10%), systemic inflammation markers (1.47%-2.10%), hematocrit (0.65%), homocysteine (4.33%), and myocardial injury enzymes (4.18%-8.62%). Increasing haze intensity was associated with a higher risk of all cardiovascular indicators. Stratified analyses revealed that males, individuals aged ≥ 50, those with higher BMI, and those with hypertension were more vulnerable to haze exposure. The haze during the cold season remains a significant public health concern in Nanjing, as even short-term exposure can significantly alter both clinical and subclinical cardiovascular indicators, including elevated blood pressure, acute systemic inflammation, increased blood viscosity, and myocardial injury.