Source: HeartWire
Author: Steve Stiles

London, UK – Tobacco use significantly ups the risk of nonfatal MI independently of its varied methods around the world and whether exposure is direct or through second-hand smoke, according to INTERHEART, a large, broadly international case-control study [1]. The findings sharpen and add a global perspective to the massive epidemiologic evidence implicating smoking and other tobacco uses as causes of heart disease.

The analysis, which appears in the August 19, 2006 issue of the Lancet, suggests that current cigarette smoking confers nearly triple the adjusted MI risk faced by persons who have never smoked and that the hazards can’t be escaped by resorting to other forms of tobacco use. The study looked at the effects of not only smokeless tobacco but also less common modes of smoking, including some that are primarily limited to specific geographic regions such as South and Central Asia.

“Our findings show that tobacco in any form is harmful,” write the authors, Dr Koon K Teo (McMaster University-Hamilton Health Sciences, Hamilton, ON) and associates. Other noteworthy observations include a significant dose-response relationship between the number of cigarettes consumed daily and the likelihood of MI, even at only a few cigarettes per day.

Commenting on the study for heartwire, Dr Ira S Ockene (University of Massachusetts Medical School, Worcester) said that it replicates much earlier work but “adds so much more,” including a global perspective not only geographically but in terms of spanning virtually all forms of tobacco exposure. Its data on the risks of chewing tobacco and second-hand smoke are important, he observed, “and it adds to what we know about the time it takes to derive a benefit from quitting.” Even most cardiologists, he said, don’t appreciate that the cardiovascular benefits of quitting are relatively rapid compared with the many years it takes for an improvement in lung-cancer risk.

In an interview with heartwire, lead author Teo also focused on the dramatic observed benefits of quitting. “Even for heavy smokers, the risk is reduced by about half. It’s never too late to quit, and the benefit comes pretty quickly. This is the message I’m telling my patients now.”

Teo et al studied tobacco-use patterns among 12 133 patients with a first acute MI and 14 435 age- and sex-matched community-based control subjects who had been recruited in 52 countries on virtually every continent. In their analysis of by far the most common use, cigarette smoking, which was adjusted for demographics, geography, and other variables:

  • Overall, the risk (odds ratio) of nonfatal MI among current smokers was 2.95 relative to that of never-smokers (p<0.0001). Risk was higher in younger smokers than in older ones and lower in women than in men.
  • The risk reached only 1.85 among former smokers within three years of quitting, although it persisted at 1.22 even among those cigarette-free for 20 years.
  • The MI risk climbed from 1.63 among persons smoking one to nine cigarettes per day to 4.59 for a rate of >20/day (p<0.0001 for both findings). Every additional daily cigarette corresponded to a 5.6% jump in risk, according to the analysis.
  • Less than half of controls reported no exposure to second-hand smoke. Those exposed only one to seven hours per week showed a significant MI risk of 1.24 relative to those without any exposure. The risk reached 1.62 for those exposed >21 hours per week.

The hazard wasn’t confined to traditional cigarettes. Smoking bidis, which the group described as “a small amount of tobacco wrapped in a dried temburini leaf and tied with a string” and more common than cigarettes in South Asia, showed a risk of 2.89 relative to tobacco nonuse. The risk for shisha smoking, or consuming tobacco through a water pipe, a common method in the Middle East, showed a risk of 2.16, they write.

Use of smokeless tobacco products was most common South-Central Asia. Chewing tobacco by itself more than doubled the MI risk. Persons who both chewed tobacco and smoked cigarettes had four times the MI risk of nonusers.

Such information can help in counseling patients from diverse cultural backgrounds who often don’t perceive alternative smoking methods to be as harmful as cigarettes, according to Teo. “If I tell my patient from say, South Asia, that a North American study showed harm [from smoking], they might say, well, you’re talking about Americans and Canadians, and I’m from a different part of the world.” The current study, he observed, should be more convincing in such cases.

“The overwhelming conclusion from this mass of data is that tobacco exposure—be it cigarettes, pipes, cigars, beedies, sheesha, or smokeless; second-hand or primary; filtered or nonfiltered, even at low levels—causes a large proportion of myocardial infarcts in men and women around the world,” write Drs Sarah A Rosner and Meir J Stampfer (Harvard School of Public Health, Boston, MA) in an accompanying editorial [2]. “The finding that very low levels of active smoking substantially increase risk lends further credence to the plausibility of second-hand smoke also being a major risk factor.”