Combined Heat and Wildfire Air Pollution Raises Cardiovascular Death Risk, Suggests Study

A new study published in the Journal of the American College of Cardiology showed that the risk of cardiovascular mortality is higher when hot weather and wildfire-related air pollution are present at the same time as when each component is present alone.

Extreme heat events and landscape fires, which may emit significant volumes of fine particle air pollution into the atmosphere, are becoming more common due to climate change. The cardiovascular system can be stressed by both heat and air pollution, but their combined consequences are less clear. Therefore, this study evaluated potential additive interactions and determine if compound exposure to heat waves and significant fire-sourced air pollution (SFAP) is linked to an increased risk of cardiovascular disease (CVD) mortality beyond single-hazard exposure.

This research analyzed national representative daily CVD mortality data in connection to heat waves, SFAP, and their co-occurrence in a multicountry time-series analysis spanning six nations. Every day was categorized into four mutually incompatible exposure states: compound exposure, heat wave-only, SFAP-only, and no hazard. They used quasi-Poisson regression to estimate relative risks (RRs) and the relative excess risk owing to interaction (RERI), attributable proportion, and synergy index to assess additive interaction.

Compound exposure was linked to an 11.5% increase in cardiovascular mortality based on 5.9 million CVD death records, surpassing the hazards associated with exposure to SFAP and heat waves alone. 598% of cardiovascular deaths during compound exposure days were associated with a modest positive additive interaction.

Heart failure (HF) mortality showed the most additive interaction, with compound exposure linked to an RR of 1.245 and 7.731% of HF fatalities during compound exposure days owing to additive interaction. For ischemic heart disease and stroke, smaller but favorable interaction effects were also noted.

The level of interactions differed between nations, with Australia showing the most impacts. The size of the predicted impacts somewhat decreased with broader buffers, but the results were consistent across different buffering windows and heat wave definitions. Overall, compared to single exposures, compound exposure to heat waves and significant fire-sourced air pollution was linked to increased cardiovascular mortality, with larger additive interaction signals for HF.

Source:

Wen, B., Wu, Y., Lavigne, E., Coelho, M., Xu, R., Chen, G., Yu, P., Liu, Y., Yu, W., Ye, T., Huang, W., Yang, Z., Zhang, Y., Xu, Z., Zhou, S., Ju, K., Saldiva, P., Matus, P., Kliengchuay, W., … Guo, Y. (2026). Compound exposure to extreme heat and substantial landscape fire-sourced air pollution on cardiovascular mortality. Journal of the American College of Cardiology. https://doi.org/10.1016/j.jacc.2026.06.005