In a large international study Canadian researchers have found that all tobacco use affects heart attack risk.
The INTERHEART study included data from more than 27,000 people in 52 countries and in their calculations, the investigators accounted for other lifestyle factors that could affect the heart attack risk, such as diet and age.
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, involved collaboration with colleagues from 52 countries.
The research team examined data for evidence that tobacco use contributes to heart attack risks and found that globally tobacco use is one of the most important causes of heart attack, especially in men.
They say all forms of tobacco use, including including "Sheesha" smoking, popular in the Middle East and "Beedie" smoking common in South Asia, was harmful and all different types of smoking and chewing tobacco and inhalation of second-hand smoke, should be discouraged.
Their results show that people who smoke triple their risk of heart attack, and increase that risk by 5.6% for every daily cigarette.
Light smokers who quit have little extra risk of heart attack three to five years after quitting.
Heavy smokers who quit see a rapid decrease in heart attack risk, but still have some extra risk even 20 years after quitting.
Chewing tobacco more than doubles heart attack risk and chewing and smoking ups the risk more than fourfold.
Just one to seven hours of secondhand-smoke exposure per week ups heart attack risk by 24 percent and more than 21 hours a week of secondhand smoke exposure ups heart attack risk by 62 percent and switching to a water pipe is no help as the risk of heart attack is still high.
The research team say no level of tobacco use was found to be safe and secondhand smoke may be even more dangerous than previously thought.
An accompanying editorial by Harvard researchers notes that smoking is predicted to kill a billion people this century and they say the study "should stimulate a redoubling of efforts to rid the planet of the scourge of smoking".
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.
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, and was also endorsed by the World Health Organization, the World Heart Federation and the International Clinical Epidemiology Network.
The study is published in the Aug. 19 issue of The Lancet.