Elevated ozone concentrations are important short-term triggers of out-of-hospital cardiac arrest in Tianjin, while high ambient temperatures showed a possible short-term association with limited statistical certainty, and exploratory analyses suggested a possible ozone-temperature interaction.
Ozone was the only air pollutant consistently associated with out-of-hospital cardiac arrest across single- and two-pollutant models.
High ambient temperature showed a possible short-term association with OHCA risk, peaking at lag 1 day, but with limited statistical certainty.
The ozone-OHCA association was comparable between men and women in sex-stratified analyses.
Heat-related risks appeared stronger in women than in men, though estimates were imprecise.
Exploratory interaction analyses suggested ozone may amplify the effect of heat on OHCA risk.
In age-specific analyses, the ≥75-year age group showed a positive trend for ozone exposure, but analyses were limited by sparse data.
The study analyzed 7,996 OHCA cases in Tianjin, China over a one-year period using a distributed lag non-linear model.
This research suggests that air pollution — specifically ozone — and high temperatures may increase the short-term risk of out-of-hospital cardiac arrest (OHCA), which is a sudden loss of heart function outside of a hospital setting. The study tracked nearly 8,000 cardiac arrest cases in Tianjin, China over one year and linked daily case counts to weather and pollution data. Among six air pollutants examined, only ozone was consistently and significantly associated with a higher risk of cardiac arrest, with each meaningful increase in ozone concentration linked to about a 15% higher risk over the following one to two days. High temperatures also appeared to raise risk, particularly the day after exposure, but the statistical evidence for this was less definitive. The study found that the ozone effect was similarly strong in both men and women. However, the temperature effect appeared larger in women than in men, though this finding was based on imprecise estimates and should be interpreted carefully. An exploratory analysis also suggested that ozone and heat together may have a combined effect larger than either alone, but the authors emphasized this should be treated as a preliminary observation requiring further investigation. This research matters because it identifies ozone as a potentially important environmental trigger for sudden cardiac events in a northern Chinese urban setting, suggesting that high-ozone days — which are common in summer — may pose a particular public health risk. The findings could inform air quality policy and public health warnings, especially for older adults and women, though the authors note that larger studies with better age-group data are needed to confirm these patterns.
Pan S, Zhang H, Li K, Zhang S, Shen R, Gao B, et al.. (2026). Ozone and possible heat effects on out-of-hospital cardiac arrest: a time-series study.. Frontiers in public health. https://doi.org/10.3389/fpubh.2026.1871041