The analysis pooled 13 studies from regions in North America, Italy, Scotland and Ireland and, despite their geographical range, found a consistent reduced risk of hospitalisation for acute myocardial infarction (AMI) of 17% (i.e. a relative risk for AMI of 0.83) at 12 months following implementation of the law. The investigators added that this benefit ‘grows with time’, reaching a gain of about 36% in three years.
The study was designed to determine the ‘consistent’ effect of smoking bans on AMI rates in communities, and was therefore concerned with both the direct and second-hand effects of smoking. Several studies have shown that the effects of second-hand smoke on many biological mediators associated with AMI risk occur rapidly and are nearly as large as those from direct smoking. For example, a study reported last year, in the Journal of American Cardiology, showed that passive exposure to second-hand smoke in as short a time as 24 hours led to ‘sustained vascular injury’ characterised by reduced endothelial function and activity of endothelial progenitor cells. According to the American Heart Association's Heart Disease and Stroke Statistics 2009 Update, non-smokers exposed to second-hand smoke at home, or at work, have a 25-30% increased risk of developing heart disease.
Since the first smoking bans were introduced (the first in Europe was in 2004 in Ireland) there have been many reports showing a decline in hospital admissions for AMI following implementation. Indeed, such laws are the best current examples of a clear association between prevention policies and cardiovascular disease. In Europe reduced AMI rates following smoking bans have been reported from France (15% decrease), Italy (11.2%), and Ireland (11%).
There have been several studies from Scotland, where smoking has been prohibited by law in all enclosed public places since March 2006. A prospective study (pub: New England Journal of Medicine) of all patients admitted to nine Scottish hospitals with acute coronary syndromes (ACS) found that the number of ACS admissions decreased from 3,235 to 2,684 following the smoking ban - a 17% reduction. This figure (the same as now found in the present meta-analysis) compared with a 4% reduction seen in England over the same study period (where no such legislation was in place at the time), and a mean annual decrease of 3% in Scotland during the decade preceding the study.
More recently, results from two other studies have been made public:
Research commissioned by the UK's Department of Health found a sharp reduction in the number of hospital admissions for AMI in England in the year following the introduction of the public smoking ban in July 2007. The research was reported as ‘incomplete’, with no precise figures given.
Icelandic research, presented at the ESC Congress 2009, showed that a nationwide smoking ban in public places resulted in a 21% reduction in ACS admissions among non-smoking men in the five months after the ban was introduced in June 2007. (No such effect was seen in women). The study population comprised 378 patients (281 men, 97 women) who underwent coronary angiography for ACS during the five months immediately before or after the ban was enacted.
Commenting on the Circulation meta-analysis for the European Society of Cardiology, spokesperson Professor Joep Perk (Oskarshamn District Hospital, Sweden) said: ‘This is an exciting and important study, with implications for both basic scientists and for politicians. First, what the analysis shows is that the harmful effect of second-hand smoke is much greater than we first imagined. It also shows that the benefits derived from the anti-smoking legislation continue over time in a linear direction. The findings, however - although impressive - still pose a challenge to our basic scientists to explain the biology of such benefits and the mechanisms that lie behind them.
‘At the public health level the results strengthen the case for anti-smoking legislation in all jurisdictions. There are still many countries in Europe without nationwide legislation, and this study should now provide the tool for wider implementation and the encouragement for braver political decisions. There seems no reason why the EU should not now advocate strong legislation in all member states. Studies like these strengthen the case for preventive cardiology.’
Prof. Perk noted that all 13 studies contributing to the meta-analysis were observational in methodology; implementation of any new anti-smoking legislation, he proposed, would also provide the framework for a large-scale prospective study to confirm the observational findings unequivocally.