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The effect of daily weather conditions on myocardial infarction incidence in a subarctic population: the Tromsø Study 1974–2004

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.