Meta-analysis of before and after studies shows a 10% reduction in acute coronary events after introduction of comprehensive smoke-free legislation
- 1The Cardiovascular Unit of Guatemala, Guatemala
- 2Washington University School of Medicine, St Louis, Missouri, USA
- Correspondence to Joaquin Barnoya
Campus Box 8100, 660 S. Euclid Avenue, St Louis, MO 63110, USA;
That tobacco (active and passive smoking) is the leading cause of cardiovascular disease (CVD) is no longer subject to debate. However, as opposed to some other CVD risk factors, we do know what works for tobacco control. From an individual and societal perspective, smoke-free environments have proven to be one of the most effective measures to prevent CVD (and other chronic diseases). Smoke-free environments decrease smoking prevalence, heart disease mortality and lung cancer incidence.1 Globally, as of November 2010, 169 nations had signed the World Health Organization Framework Convention on Tobacco Control and, partially stimulated by it, as of January 2011, 55 countries had some sort of smoke-free law, 37 of which include both bars and restaurants.2 A comprehensive smoke-free law is one that mandates all workplaces (regardless of size, alcohol sales and location) to ban smoking indoors. Among workplaces, bars and restaurants have the highest levels of second-hand smoke (SHS) exposure3 4 and so often see the greatest reductions in exposure when these laws are implemented.
The rigorous meta-analysis by Mackay and colleagues adds to the body of literature confirming that a comprehensive smoke-free law leads to a reduction in acute coronary events. Combining data from 17 studies that provided 35 estimates, the authors report a significant overall 10% reduction in incidence of acute coronary events following introduction of smoke-free legislation. They note significant heterogeneity in results; although earlier small studies showed larger effects, the small study bias was not significant. In five of the subgroup analyses (individuals 50 years of age and older and in New Zealand) the risk of acute coronary syndrome was not reduced. However, after adjustment for other study characteristics, age category and study location were no longer significant predictors of risk reduction. Only ‘months of follow-up after legislation’ is a significant predictor in the model; the longer the follow-up, the larger the risk reduction. For each year of follow-up after legislation there was a significant 6% reduction in acute coronary events.
The authors used state-of-the-art methods, a clearly defined question, search of the literature (including numerous databases) and defined eligibility criteria for inclusion of studies. Two of the authors conducted an independent systematic review to reduce potential bias and error; however, there is no mention of abstractor agreement and how disagreements were resolved. For those studies that did not provide population denominators, these were obtained from official government censuses. The authors then conducted analyses using random effects models that accounted for within-study and between-study variability (more conservative than a fixed-effects model). Appropriate assessments of heterogeneity (funnel plot and test of Egger) were conducted, and p values were adjusted for multiple testing.
This meta-analysis is in agreement with two earlier reports based on a smaller set of studies. The current review yields a 10% reduction compared to the 17% previously reported after the implementation of this legislation.5 6 Data from New Zealand, England, Canada and Arizona have been added in Mackay's review. Several reasons might account for the difference observed in the magnitude of risk reduction. Length of follow-up, population characteristics, smoking prevalence, SHS exposure before the ban, end points, confounders considered and law enforcement are all to be considered (and also account for study heterogeneity 6).
Regardless of, and supporting, the 2010 Institute of Medicine report on SHS and cardiovascular effects,1 it is now reasonable to conclude that there is a causal relationship between smoking bans and a decrease in acute coronary events. The longer the ban is in place, the larger the decrease in risk. Furthermore, implementing a smoke-free workplace law is more cost-effective than a free nicotine replacement programme at promoting smoking cessation ($799 and $7020 per quitter, respectively8). Why then is 93% of the world population still exposed to SHS? The answer lies in the well-orchestrated lobbying and misinformation campaign lead by the tobacco industry.7 Given the relentless efforts by manufacturers to promote smoking, nurses and healthcare professionals should actively and routinely advocate through their professional organisations for the implementation of smoke-free environments (at work and at home). From a clinical standpoint, all patients (adults, children and parents) should be advised to avoid SHS exposure and to demand a smoke-free environment. Millions of unnecessary health events could be prevented annually.
Competing interests JB is partially supported by an unrestricted grant from the American Cancer Society. GAC is supported by an American Cancer Society Clinical Research Professorship.