Cold weather snaps can trigger heart attacks, particularly in people suffering from high blood pressure, researchers said on Monday.

The increased rate of attacks seen during wintertime lows is probably due to the fact that cold temperatures increase blood pressure and put more strain on the heart.

A 2-year study of 700 people admitted to hospital in France found the occurrence of heart attacks in people with hypertension, or high blood pressure, was twice as high when the mean temperature was lower than minus 4 Celsius (24.8 Fahrenheit).

They also had a 62 percent greater risk of heart attack when the temperature difference between the day before and the day of the attack was more than 5 degrees Celsius.

Yves Cottin and Marianne Zeller of the University of Dijon told the annual meeting of the European Society of Cardiology that susceptible people should be careful about activities in cold weather or when temperatures change suddenly.

Their study also found a link with low barometric pressure, with more heart attacks occurring during a cold weather front.

In addition to a general rise in blood pressure, colder weather can cause blood to become stickier and more likely to clot.

Cholesterol levels also tend to be higher during the winter and an increase in respiratory infections may lead to inflammation that contributes of the rupture of artery-clogging plaques.