A major Canadian-led global study has found all forms of tobacco exposure, whether that be smoking, chewing or inhaling second hand smoke, increase the risk of heart attack.
The study by professors Salim Yusuf and Koon Teo of the Michael G. DeGroote School of Medicine at McMaster University and Hamilton Health Sciences in Hamilton, is published in this week's issue of The Lancet.
In collaboration with colleagues from 52 countries, they calculated the risk of heart attack for various forms of active tobacco use (both smoking and non-smoking) and second hand smoking in all areas of the world. The INTERHEART study included data from more than 27,000 people in 52 countries. In their calculations, the investigators accounted for other lifestyle factors that could affect the heart attack risk, such as diet and age.
They found that tobacco use in any form, including sheesha smoking popular in the Middle East and beedie smoking common in South Asia, was harmful. Compared to people who had never smoked, smokers had a three-fold increased risk of a heart attack. Even those with relatively low levels of exposure of eight to 10 cigarettes a day doubled their risk of heart attack. Each cigarette smoked per day, increased the risk by 5.6 per cent.
However, the researchers did find that the risk of heart attack decreased with time after stopping smoking. Light smokers, those who consume fewer than 10 cigarettes a day, benefit the most. They have no excess risk three to five years after quitting. By contrast, moderate and heavy smokers of 20 or more cigarettes a day still had an excess risk of around 22 per cent, 20 years after quitting.
The team also found that exposure to second hand smoke increased the risk of heart attack in both former and non-smokers. The findings suggest that individuals with the highest levels of exposure to second hand smoke of 22 hours or more per week may increase their risk of heart attack by around 45%.
"Chewing tobacco also increased the risk of a heart attack two fold, indicating that all forms of tobacco use or exposure are harmful," said Dr. Koon Teo.
Dr. Yusuf 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 promote quitting in current smokers, will have a large impact in prevention of heart attack worldwide."
The number of smokers worldwide is currently estimated to be 1.3 billion, of which 82% are in developing countries. However, most large studies on smoking and heart disease to date have focused on developed countries.
"Smoking is the leading preventable cause of death, killing 47,000 Canadians each year through direct smoking and exposure to second-hand smoke," said Rocco Rossi, CEO, Heart and Stroke Foundation of Ontario. "We have been a successful advocate for a smoke free Ontario and have achieved one of the strongest pieces of anti-tobacco legislation in North America. This study provides more evidence why it's critical for everyone to become and remain smoke free, and will encourage governments to take effective action to protect their people from the dangers of tobacco."
"People around the world should pay attention to the message that it's never too late to quit. This is an important study documenting the powerful and persistent dangers of tobacco use worldwide," said Dr. Peter Liu, scientific director for CIHR's Institute of Circulatory and Respiratory Health (ICRH). "Canadians can be proud that we lead the world in efforts to prevent and reverse the trend in smoking. But we cannot rest on our laurels, and must do better still to protect our citizens."
"Data like this bolsters anti-smoking efforts worldwide," said Dr. Jennifer Everson, a family physician and vice president, medical at Hamilton Health Sciences. "It's important, additional evidence that we can share with our patients to help them make choices that could save their lives."
The INTERHEART study was funded by the Canadian Institutes of Health Research (CIHR), the Heart and Stroke Foundation of Ontario and 37 funding sources, including unrestricted support from several pharmaceutical companies.
The study was endorsed by the World Health Organization, the World Heart Federation and the International Clinical Epidemiology Network.