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The effect of daily weather conditions on myocardial infarction incidence in a subarctic population: the Tromsø Study 1974–2004
  1. Laila Arnesdatter Hopstock1,
  2. Ane Schwenke Fors2,
  3. Kaare Harald Bønaa1,3,4,
  4. Jan Mannsverk1,5,
  5. Inger Njølstad1,
  6. Tom Wilsgaard1
  1. 1Department of Community Medicine, University of Tromsø, Tromsø, Norway
  2. 2Department of Physics and Technology, University of Tromsø, Tromsø, Norway
  3. 3Unit of Applied Clinical Research, Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, Trondheim, Norway
  4. 4Department of Heart Disease, St. Olavs University Hospital, Trondheim, Norway
  5. 5Department of Heart Disease, University Hospital of Northern Norway, Tromsø, Norway
  1. Correspondence to Laila Arnesdatter Hopstock, Department of Community Medicine, University of Tromsø, N-9037 Tromsø, Norway; laila.hopstock{at}


Background Meteorological factors like cold temperatures and heavy snowfalls have been reported to increase myocardial infarction (MI) incidence, but there are inconsistencies in results as well as in methodology in previous studies. The objective of this study was to examine the impact of meteorological factors on incidence of MI in a population-based study in Tromsø, Norway (69°39′N).

Methods A total of 32 110 participants from the Tromsø Study enrolled between 1974 and 2001 were followed throughout 2004. Each incident case of MI was validated by the review of medical records and death certificates. Meteorological data from the Tromsø Weather Station were collected from the Norwegian Meteorological Institute database. Poisson regression models were applied to analyse the impact of meteorological factors on MI incidence. All analyses were stratified by sex and age.

Results A total of 1882 first-ever MIs were registered. The main finding was an increase in MI incidence among persons older than 65 years with decreasing temperatures (p=0.016) and increasing snowfall (p=0.030). When comparing the lower and upper limits of the temperature distribution (−10°C with 20°C), the MI risk increased by 47% (RR=1.47, 95% CI 1.09 to 2.13). Comparing limits of the snowfall distribution (10 with 0 mm), the MI risk increased by 44% (RR=1.44, 95% CI 1.07 to 1.94).

Conclusions In this subarctic population, MI incidence was little affected by the weather, probably due to behavioural protection. However, cold weather and heavy snowfall may be associated with increased risk of MI among older people.

  • Epidemiology
  • myocardial infarction/heart disease
  • seasons/seasonal variation
  • climate

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  • Competing interests None.

  • Ethics approval This study was conducted with the approval of the Regional Board of Research Ethics, the Data Inspectorate and the Directorate of Health and Social Affairs.

  • Provenance and peer review Not commissioned; externally peer reviewed.