All forms of tobacco exposure--smoking, chewing or inhaling second hand smoke--increase the risk of heart attack up to three times, according to an Article in this week's issue of The Lancet.
Previous studies have shown that tobacco smoking increases the risk of heart disease. However, to date most of these studies have been in developed countries and few large studies have been done to examine the effects of tobacco in other geographical regions.
In the INTERHEART study, Salim Yusuf and Koon Teo (McMaster University, Ontario, Canada) and colleagues calculated the risk of heart attack for various forms of active tobacco use (both smoking and non-smoking) and second hand smoking (SHS) in all areas of the world. The study included data from over 27 000 people in 52 countries. The investigators adjusted their calculations to exclude the effect of other lifestyle factors that could affect 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 (8-10 cigarettes a day) doubled their risk of heart attack. However, the researchers did find that the risk of heart attack decreased with time after stopping smoking; among light smokers (<10 cigarettes a day) there was no excess risk 3-5 years after quitting. By contrast, moderate and heavy (20> cigarettes a day) smokers still had an excess risk of around 22%, 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 SHS (22 hours or more per week) may increase their risk of heart attack by around 45%.