Short-Term Effects of Lower Air Temperature and Cold Spells on Myocardial Infarction Hospitalizations in Sweden

Lower air temperature and cold spells have been associated with an increased risk of various diseases. However, the short-term effect of lower air temperature and cold spells on myocardial infarction (MI) remains incompletely understood. The purpose of this study was to investigate the short-term effects of lower air temperature and cold spells on the risk of hospitalization for MI in Sweden. This population-based nationwide study included 120,380 MI cases admitted to hospitals in Sweden during the cold season (October to March) from 2005 to 2019. Daily mean air temperature (1 km2 resolution) was estimated using machine learning, and percentiles of daily temperatures experienced by individuals in the same municipality were used as individual exposure indicators to account for potential geographic adaptation. Cold spells were defined as periods of at least 2 consecutive days with a daily mean temperature below the 10th percentile of the temperature distribution for each municipality. A time-stratified case-crossover design incorporating conditional logistic regression models with distributed lag nonlinear models using lag 0 to 1 (immediate) and 2 to 6 days (delayed) was used to evaluate the short-term effects of lower air temperature and cold spells on total MI, non–ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI). A decrease of 1-unit in percentile temperature at a lag of 2 to 6 days was significantly associated with increased risks of total MI, NSTEMI, and STEMI, with ORs of 1.099 (95% CI: 1.057-1.142), 1.110 (95% CI: 1.060-1.164), and 1.076 (95% CI: 1.004-1.153), respectively. Additionally, cold spells at a lag of 2 to 6 days were significantly associated with increased risks for total MI, NSTEMI, and STEMI, with ORs of 1.077 (95% CI: 1.037-1.120), 1.069 (95% CI: 1.020-1.119), and 1.095 (95% CI: 1.023-1.172), respectively. Conversely, lower air temperature and cold spells at a lag of 0 to 1 days were associated with decreased risks for MI. This nationwide case-crossover study reveals that short-term exposures to lower air temperature and cold spells are associated with an increased risk of hospitalization for MI at lag 2 to 6 days.