PEOPLE exposed to cigarette smoke for as little as an hour a day increase their risk of a heart attack by almost a quarter, a study indicates.

Those exposed to three hours of passive smoke daily were found to increase their risk by more than 60 per cent.

The findings of the Interheart study, which looked at the experience of 27,000 people in 52 countries, will reinforce efforts to reduce smoking in public places. It looked at all tobacco exposure, active and passive, and found that all increase the risk of cardiac arrest.

Heart attacks were three times as common in smokers than in people who had never smoked.

Every cigarette smoked per day added 5.6 per cent to the risk, but quitting does bring benefits. Within three years the extra risk for 20-a-day smokers falls from almost 300 per cent to 87 per cent. If they remain ex-smokers for 20 years, their extra risk drops to 22 per cent.

In the case of people who smoked fewer than ten cigarettes a day, there was no excess risk three to five years after quitting. Chewing tobacco more than doubled the risk, as did smoking eight to ten cigarettes a day.

Professor Salim Yusuf, of McMaster University in Ontario, Canada, led the study, which was published in The Lancet. He said: “Since the risks of heart attack associated with smoking dissipate substantially after smoking cessation, public health efforts to prevent people from starting the habit and to promote quitting in current smokers will have a large impact in the prevention of heart attacks worldwide.”

Heart attack risk was directly linked to the number of cigarettes a person smoked, the study suggested.

The risk rose 1.63 times for people smoking one to nine cigarettes a day, increasing to 9.16 times for those who smoked 40 or more. Similar trends were seen for men and women. The impact of smoking was much greater in younger than in older individuals.

During the 20th century about 100 million people around the world died from tobacco-related diseases, the researchers said. The number is expected to increase to one billion during this century.

Amanda Sandford, research manager of ASH (Action on Smoking and Health) said: “This important study shows that even small amounts of tobacco use can have a devastating health impact. ”

Ruairi O’Connor, of the British Heart Foundation, said: “The good news is that much of the added risk of a heart attack recedes after quitting — a great reason to kick the habit.”

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