A global study conducted in 52 countries has confirmed that the risk of acute myocardial infarction (AMI) increases with all tobacco exposure, be it from cigarettes, beedies, sheesha, chewable forms, or even second-hand smoke.
Researchers from the INTERHEART case-control study examined data on 12,461 individuals with AMI and 14,637 age- and gender-matched controls from 262 centres in Asia, Europe, the Middle-East Crescent, Africa, Australia, and North and South America.
The team, led by Koon Teo (McMaster University, Hamilton, Ontario, Canada), found a close link between the level of exposure and risk.
"Among smokers, even low levels of smoking (about 8 to 10 cigarettes per day) increase the risk of AMI two-fold," the investigators report in The Lancet.
Current smoking was associated with a three-fold increase in the odds of nonfatal AMI compared with never smoking (odds ratio [OR]=2.95).
Each cigarette increased AMI risk by 5.6 per cent. However, Teo et al note: "In light smokers (<10 cigarettes a day), the excess risk fell rapidly, with no apparent excess risk 3 years after quitting."
Risk fell more slowly in heavier smokers consuming 20 cigarettes a day, in whom the risk of AMI remained raised 20 years after quitting (OR=1.22), with the largest decrease occurring in the first 3 years.
Smoking beedies alone, which is common in South Asia, was associated with an AMI risk similar to that seen with cigarettes (OR=2.89). Although chewing tobacco was associated with a slightly lower risk (OR=2.23), smokers who also chewed tobacco had the greatest increase in risk (OR=4.09).
The AMI risk with second-hand smoke increased with exposure, from the least exposed at 1-7 hours per week (OR=1.24) to the most exposed at more than 21 hours per week (OR=1.62).
Population attributable risk was highest in young male current smokers, at 58·3 per cent, and was lowest in older women, at 6·2 per cent. Population attributable risk for exposure to second-hand smoke for more than 1 hour per week in never-smokers was 15·4 per cent.
In an editorial accompanying the article, Sarah Rosner and Meir Stampfer (Harvard School of Public Health, Boston, Massachusetts, USA) wrote: "During the present century, about 1 billion people will die of smoking-related conditions if current trends persist; a substantial proportion due to cardiovascular disease."
"The latest findings from INTERHEART should stimulate a redoubling of our efforts to rid the planet of the scourge of smoking," they added.