ORLANDO – Cold temperature days were associated with a 28% increase in the risk of MI and a 15% increase in stroke over an 18-year period in Ontario, Hong Chen, Ph.D., reported at the American Heart Association scientific sessions.

The relationship between air temperature and cardiovascular events mapped out as a U-shaped pattern, with the lowest-risk trough occurring on days when the temperature averaged 54º F. However, the U-shape was skewed such that the increased risk achieved significance on the cold but not hot days, according to Dr. Chen of Public Health Ontario and the University of Toronto.

He and his coinvestigators looked at the relationship between daily temperature and cardiovascular risk because the epidemiologic data in this area was sparse even though there are intriguing animal studies suggesting that extreme cold weather can induce a prothrombotic inflammatory reaction and hypercoagulable state.

The investigators matched daily temperature and cardiovascular hospital admission data for all 14 health districts in the sprawling province of Ontario for the period 1996-2013. During the study period, there were 443,447 hospitalizations for acute MI, 355,837 for stroke, 237,979 for ischemic stroke, and 1.4 million admissions coded as ischemic heart disease.

In a multivariate analysis controlling for influenza activity, air pollution levels, relative humidity, and day of the week, the adjusted rate of admissions for MI was 28% greater on the coldest 1% of days than on days where the temperature averaged the optimal 54º F. The coldest days were also associated with a 12% increase in the risk of admission for ischemic heart disease, a 15% increase in stroke, and a 19% increase in ischemic stroke.

Dr. Chen and his coworkers also examined their mountain of data to see how selected comorbid conditions might affect temperature-related risk. They found that the risk of admission for ischemic heart disease on cold days was greatest among individuals with a history of conduction disorders, while the risk of cold-related stroke was highest in Ontarians with preexisting arrhythmias.

Dr. Chen reported having no financial conflicts of interest regarding this public health study.

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