MI risk rises as temperatures drop
MedWire News: Cold outdoor temperatures may increase the risk for myocardial infarction (MI), especially among elderly patients with a history of coronary heart disease (CHD) report UK researchers.
However, the team found no increase in risk for MI at high temperatures despite reports of such an association by previous studies.
Explaining the potential impact of their findings in the British Medical Journal, Krishnan Bhaskaran (London School of Hygiene and Tropical Medicine) and colleagues say: "Because MIs are common and ambient temperatures are experienced by the whole population, even a small increase in risk translates to substantial absolute numbers of extra MIs."
They add: "Our results suggest that each 1°C reduction in temperature nationwide on a single day would be associated with around 200 extra MI events."
In an accompanying editorial, Paola Michelozzi and Manuela De Sario (Lazio Region Department of Epidemiology, Rome, Italy) stressed the relevance of these findings to the current global climate change which will bring extremes of both cold and hot weather. They called for "actions to reduce greenhouse gases based on lifestyle changes at the population and individual level."
Bhaskaran et al analyzed the rate of MI hospital admissions in England and Wales during 2003 to 2006, and compared them with daily temperatures in the same areas.
Over the 3-year period, 84,010 MI admissions occurred at a median rate of 57 MIs per day.
After adjustment for confounding factors such as influenza activity and air pollution, the team found an inverse linear relationship between local temperature and MI rate, with each 1°C reduction in daily mean temperature associated with a cumulative increase in MI risk for that day and the subsequent 28 days, of 2%.
The greatest risk for MI occurred 2-7 and 8-14 days after a reduction in temperature, with 0.6% and 0.7% increases in MI risk per 1°C reduction in temperature, respectively (p=0.054 and p=0.006, respectively).
Of note, aspirin appeared to have some protective effect, with patients taking aspirin having a 1.6% increase in MI risk per 1oC temperature reduction, whereas those not taking the drug had a 2.2% risk increase (p for interaction=0.007).
In contrast, older patients aged 75 to 84 years, and patients with a history of CHD were found to have the greatest risk for MI during cold temperatures, with 2.7% and 2.5% increases in MI risk per 1°C reduction in temperature, respectively (p<0.001).
Bhaskaran et al conclude: "International studies with consistent methods will be required to clarify the dependence of these effects on local climate."
They add that individual studies on the role of preventive measures such as home heating are also required.
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By Lauretta Ihonor