Cold weather can raise a person's risk of getting a heart attack, says a study led by an Indian-origin researcher.
Krishnan Bhaskaran and colleagues from London School of Hygiene and Tropical Medicine have found that a drop in the average temperature outside is linked to higher risk of people having heart attacks, the 'British Medical Journal' reported.
In fact, each 1°C reduction in temperature on a single day is associated with around 200 extra heart attacks in UK.
Though the reasons behind the increased risk in cooler temperatures is not yet clear, the researchers think it could be down to changes in blood pressure and even blood thickness in colder weather.
For their study, the researchers analysed data on 84,010 patients admitted to hospital with a heart attack in 2003-2006, compared with daily temperatures in England and Wales at the same time.
The results were adjusted to take into account other risk factors like air pollution and rates of flu at the time.
The researchers found that a 1°C drop in average daily temperature was linked to a 2 per cent increase in the risk of heart attack over the next 28 days. The risk was highest in the following two weeks.
The researchers said while the risk appeared small, there were 146,000 heart attacks every year in the UK so even a small increase in risk translated into 200 extra heart attacks for each 1°C drop on a single day.
The highest risk was within two weeks of exposure, according to a statement of the London School.
The heightened risk may seem small, but Britain alone has an estimated 146,000 heart attacks a year and 11,600 events in a 29 day period.
Even a small increase in risk translates to substantial numbers of extra heart attacks, around 200 for each one degree Celsius reduction in temperature nationwide on a single day.
Older people aged between 75 and 84 years 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.
The researchers found no increase in the risk of heart attacks at higher temperatures, possibly because temperature in Britain is rarely very high in global terms.