London, Aug 11 (IANS): A fall in temperature even by a degree on a single day can bring on 200 extra heart attacks, a study says.

Researchers from the London School of Hygiene and Tropical Medicine carried out the study 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 during 2003-2006, and daily temperatures from the British Atmospheric Data Centre, reports the journal bmj.com.

Researchers found that a one degree Celsius reduction in average daily temperature was associated with a cumulative two percent increase in risk of heart attack for 28 days.

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.