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Original Investigation
November 2018

Association of Weather With Day-to-Day Incidence of Myocardial Infarction: A SWEDEHEART Nationwide Observational Study

Author Affiliations
  • 1Department of Cardiology, Clinical Sciences, Lund University, Lund, Sweden
  • 2Örebro University, Faculty of Health, Department of Cardiology, Örebro, Sweden
  • 3Department of Cardiology, Linköping University Hospital, Linköping, Sweden
  • 4Karolinska Institutet, Department of Medicine Huddinge, Sweden
  • 5National Heart Centre Singapore, 5 Hospital Drive, Singapore
  • 6Department of Cardiology, Clinical Science and Education, Södersjukhuset, Stockholm, Sweden
  • 7Department of Clinical Sciences, Danderyds University Hospital, Karolinska Institutet, Stockholm, Sweden
  • 8Cardiovascular Division, Brigham and Women's Hospital, Boston, Massachusetts
JAMA Cardiol. 2018;3(11):1081-1089. doi:10.1001/jamacardio.2018.3466
Key Points

Question  Is the incidence of myocardial infarction affected by different weather conditions?

Findings  In this nationwide population-based study, a higher incidence of myocardial infarction in Sweden was observed at days with low air temperature, low atmospheric air pressure, high wind velocity, and shorter sunshine duration.

Meaning  This study adds to knowledge on the role of weather as potential trigger of myocardial infarction.


Importance  Whether certain weather conditions modulate the onset of myocardial infarction (MI) is of great interest to clinicians because it could be used to prevent MIs as well as guide allocation of health care resources.

Objective  To determine if weather is associated with day-to-day incidence of MI.

Design, Setting, and Participants  In this prospective, population-based and nationwide setting, daily weather data from the Swedish Meteorological and Hydrological Institute were extracted for all MIs reported to the Swedish nationwide coronary care unit registry, Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART), during 1998 to 2013 and then merged with each MI on date of symptom onset and coronary care unit. All patients admitted to any coronary care unit in Sweden owing to MI were included. A total of 280 873 patients were included, of whom 92 044 were diagnosed as having ST-elevation MI. Weather data were available for 274 029 patients (97.6%), which composed the final study population. Data were analyzed between February 2017 and April 2018.

Exposures  The nationwide daily mean air temperature, minimum air temperature, maximum air temperature, wind velocity, sunshine duration, atmospheric air pressure, air humidity, snow precipitation, rain precipitation, and change in air temperature.

Main Outcomes and Measures  The nationwide daily counts of MI as outcome.

Results  In 274 029 patients, mean (SD) age was 71.7 (12) years. Incidence of MI increased with lower air temperature, lower atmospheric air pressure, higher wind velocity, and shorter sunshine duration. The most pronounced association was observed for air temperature, where a 1-SD increase in air temperature (7.4°C) was associated with a 2.8% reduction in risk of MI (unadjusted incidence ratio, 0.972; 95% CI, 0.967-0.977; P <.001). Results were consistent for non–ST-elevation MI as well as ST-elevation MI and across a large range of subgroups and health care regions.

Conclusions and Relevance  In this large, nationwide study, low air temperature, low atmospheric air pressure, high wind velocity, and shorter sunshine duration were associated with risk of MI with the most evident association observed for air temperature.