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%.'"/>