Ambient cold exposure and myocardial infarction risk in Tianjin, China: a distributed lag non-linear analysis

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Abstract Background Ambient temperature is an important environmental determinant of cardiovascular health. Although cold exposure has been associated with acute myocardial infarction (MI), evidence on delayed effects and subtype-specific differences remains limited in northern China. We examined the short-term association between temperature and MI incidence in Tianjin. Methods We conducted a time-series study integrating daily MI counts from the Tianjin Chest Pain Center with meteorological data from 2020 to 2023. Distributed lag non-linear models with quasi-Poisson regression were used to estimate non-linear and lagged effects of temperature on MI, adjusting for long-term trends, seasonality, relative humidity, day of the week, and public holidays. Extreme cold was defined as the 5th percentile of daily mean temperature (− 3.4 °C). The minimum morbidity temperature (MMT) was used as the reference temperature. Results During the 1,461-day study period, 34,940 MI events were recorded, including 21,814 (62.4%) STEMI cases. Compared with the median temperature (15.4 °C), extreme cold was associated with a cumulative 7-day RR of 1.53 (95% CI: 1.25–1.87), with peak effects observed at lag 2 days. The cumulative risk appeared higher for STEMI (RR = 1.62, 95% CI: 1.31–2.01) than NSTEMI (RR = 1.38, 95% CI: 1.05–1.82), but this difference was not statistically significant ( P heterogeneity = 0.367). Referenced to the MMT, the temperature–MI association showed a non-linear, approximately U-shaped pattern, with extreme cold associated with increased risk (RR = 1.66, 95% CI: 1.35–2.04). The bootstrap-derived MMT was 24.1 °C (95% CI: 22.6–26.2 °C), consistent with the primary estimate. Conclusions Ambient cold exposure is associated with a short-term increase in MI risk in Tianjin, peaking approximately 2 days after exposure. Although STEMI showed higher descriptive risk than NSTEMI, no statistically significant difference was observed. Heat-related associations were not statistically significant and should be interpreted cautiously due to limited exposure frequency and statistical power. These findings provide evidence for cold-related cardiovascular risk in temperate regions. Clinical trial registration Not applicable.