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Cold weather may raise the risk of heart attacks, according to a new study.

Air pollution and temperature changes are the most frequently cited environmental triggers for heart attacks. While research has mainly focused on one environmental condition, experts say environmental triggers are related to each other and may attenuate or reinforce the triggering effect of a single environmental factor.

"Better knowledge of the impact of environment on acute myocardial infarction will help medical care providers and policy makers to optimize prevention strategies for a target risk population," lead researcher Professor Claeys said in a news release.

The latest research examined the independent environmental triggers of heart attack.  Researchers looked at the air pollution expressed as particulate matter both less than 10µM (PM10) and less than 2.5µM (PM2.5), black smoke, temperature and relative humidity.

Researchers found a significant positive correlation between heart attack and air pollution and an inverse correlation between heart attack and temperature.

Further analysis revealed a 7 percent increase in heart attack risk for every 10°C decrease in minimal temperature. However, there was no significant effect of air pollution on heart attack risk.

"Additional analysis showed that the triggering effect of low temperature was also present outside the winter period. Apparently, smaller differences in temperature between indoor and outdoor can also precipitate AMI. In addition, below a minimal temperature of 10°C there is no additional effect of temperature decrease on the occurrence of acute myocardial infarction," Claeys said.

Researchers said that cold weather increases the risk of coronary events because low temperatures trigger stimulation of cold receptors in the skin and therefore the sympathetic nervous system, leading to a rise in catecholamine levels.  Furthermore, increased platelet aggregation and blood viscosity during cold exposure can encourage thrombosis and clot formation.

"In a global environmental model, low temperature is by far the most important environmental trigger for AMI, whereas air pollution has a negligible effect. People at risk of AMI (for example elderly patients with diabetes and hypertension) can minimise their risk by avoiding big changes in temperature. This means wearing suitable clothes when going from the warm indoors to the colder outdoors, even beyond winter time," Claeys concluded.