updated 8/10/2010 8:46:26 PM ET 2010-08-11T00:46:26

Enjoy the heat this summer. Cold weather brings more than a chill to your bones, a new study suggests. It could also raise your risk of having a heart attack.

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The results show that each 1.8 degree Fahrenheit reduction in temperature on a single day is associated with around 200 additional heart attacks.

The results are published online today in the British Medical Journal.

In the light of global climate change, the relations between weather and health are of increasing interest. Previous studies have shown that outdoor temperature is linked to mortality risk in the short term, with both hot and cold days having an effect, but the effect of temperature on the risk of heart attacks (called myocardial infarctions) is unclear.

Researchers from the United Kingdom analyzed data on 84,010 hospital admissions for heart attacks recorded in 2003-2006. They also looked at the daily temperatures from the British Atmospheric Data Center, focusing on 15 geographical areas in England and Wales.

The results were adjusted to take into account factors that might influence the heart attack rate, including air pollution and influenza activity.

The researchers found that a 1 degree-Celsius reduction in average daily temperature was associated with a cumulative 2 percent increase in risk of heart attack over a 28-day period. The highest risk was within two weeks of exposure to cold weather.

The heightened risk may seem small, but the U.K. 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 a few hundred extra heart attacks on a single day.

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.

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There was no link between higher temperatures and increased risk of heart attack, but this might be because temperatures in the U.K. are rarely very high compared with other regions in the world.

The researchers aren't sure exactly what's behind the link, but evidence from laboratory studies on cold exposure suggests clues. Cold temperatures are known to raise blood pressure and also increase levels of certain proteins that could increase the risk for blood clots.  

Certain activities more commonly performed during cold weather, such as snow shoveling, might also contribute to the risk, the researchers say.

Studies performed in different parts of the world will be needed to determine how dependent this link is on the local climate, the researchers say. Future investigations could also shed light on which groups are most vulnerable to heart attacks linked with the cold as well as ways to prevent the risk, such as advising patients, particularly the elderly, to wear suitable clothing and to heat their homes sufficiently.

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