NEW DELHI: Harsh winters are bad news for heart patients as cold weather triggers heart attacks, particularly in people suffering from high blood pressure.

Cardiologists say the increased rate of attacks seen during winter is because low temperature increases blood pressure and puts more strain on the heart.

A general rise in blood pressure can also prove lethal with colder weather causing the blood to become stickier and more likely to clot.

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

Speaking to TOI , chief cardiologist of Escorts Heart Research Centre Dr R R Kasliwal said: "The occurrence of heart attacks in people with hypertension and high blood pressure is twice as high during winter. Cold causes spasm of arteries causing angina or heart attacks. Also, cold winter mornings cause peripheral arteries to contract, increasing the blood pressure and putting extra load on the heart. This precipitates a stroke. Strokes during early morning in winter are very common."

Cardiologists say patients who walk very early in the morning should avoid the cold. They can suffer accidental hypothermia which means the body temperature falls below normal.

It occurs when the body can't produce enough energy to keep the internal body temperature warm enough. Heart failure causes most deaths in hypothermia.

Dr S K Gupta, head of cardiology at Apollo Hospital, added: "High blood pressure is a well-known risk factor for heart disease and stroke but the risk goes up as the temperature goes down. High BP causes twice as many heart attacks during cold weather as they do on warmer days. The adrenaline level is highest early in the morning. Because the body has to stay warm, it pumps glucose and adrenaline more rapidly which increases the workload on the heart."

A Cardiologist Society of India official said: "As people age, their ability to maintain a normal internal body temperature often decreases. Because elderly people seem to be relatively insensitive to moderately cold conditions, they can suffer hypothermia without knowing they are in danger. People with coronary heart disease often suffer chest pain or discomfort called angina pectoris during cold weather."

Scientists from the University of Burgundy in France recently presented studies which found a higher number of heart attacks among blood pressure patients — in those with pressure higher than 140/90 — when temperatures dropped by more than nine degrees on the day of their heart attack.

The connection stems from the fact that blood vessels constrict in cold weather, making it harder for blood to flow through the body.