The colder it is outside, the higher the risk of suffering a heart attack, the results of a new study indicate.
UK researchers found that each one degree Celsius reduction in temperature on a single day was associated with a significant number of extra heart attacks.
The team from the London School of Hygiene and Tropical Medicine set out to examine the short-term relation between ambient temperature and risk of heart attack.
They analysed data on 84,010 hospital admissions for heart attack recorded in 15 geographical areas in England and Wales between 2003 and 2006. The results were adjusted to take into account factors such as air pollution and influenza activity.
The study found that a one degree Celsius reduction in average daily temperature was associated with a cumulative 2% increase in risk of heart attack for 28 days. The highest risk was within two weeks of exposure.
The heightened risk may seem small, but the researchers pointed out that the UK has an estimated 146,000 heart attacks a year and 11,600 events in a 29 day period, so even a small increase in risk translates to substantial numbers of extra heart attacks - around 200 for each one degree Celsius reduction in temperature on a single day.
The study noted that older people between the ages of 75 and 84 and those with previous coronary heart disease seemed to be more vulnerable to the effects of temperature reductions, while people who had been taking aspirin long-term were less vulnerable.
"Our study shows a convincing short-term increase in risk of myocardial infarction (heart attack) associated with lower ambient temperature, predominantly operating in the two weeks after exposure," the researchers concluded.
They called for further studies to help shed light on the role of adaptive measures such as clothing and home heating, and further clarify which groups are likely to be the most vulnerable.
Details of these findings are published in the British Medical Journal. In an accompanying editorial, Dr Paola Michelozzi and Manuela De Sario, of the Lazio Region Department of Epidemiology in Rome, commented that heat and cold exposure affect people with cardiovascular diseases ‘and increase the incidence of coronary events with high impact on short-term mortality'.
"Moreover, while the effect of cold on myocardial infarction is well documented, the short-term effect of heat is still contradictory but cannot be disregarded.
"This is even more relevant under climate change scenarios that predict a decrease of cold related mortality that will be outweighed by an increase in cardiovascular mortality and morbidity associated with increased frequency and intensity of heat waves," they said.
They added that doctors should be aware that exposure to environmental heat and cold is a risk factor for cardiovascular disease ‘and should consider this in risk prevention and management'.
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