Pueblo, CO - The reduction in MI hospitalizations observed after a smoke-free law takes effect appears to be sustained over an extended period, according to a new study from Pueblo, CO [1].

The study, reported in the January 2, 2009 issue of the Center for Disease Control and Prevention's (CDC's) Morbidity and Mortality Weekly Report, examined MI hospitalization rates before and after the implementation of a municipal law in the city of Pueblo making workplaces and public places smoke-free.

Results showed that MI hospitalizations for city residents decreased by 27% in the initial 18-month period (phase 1) after the smoke-free law came into effect on July 1, 2003. In addition, MI hospitalizations decreased by a further 19% during the following 18 months—through to June 30, 2006 (the phase 2 period).

No significant changes in MI hospitalizations were observed in two nearby comparison areas that did not have smoke-free laws in place before or during the study periods. "These findings suggest that smoke-free policies can result in reductions in AMI hospitalizations that are sustained over a three-year period and that these policies are important in preventing morbidity and mortality associated with heart disease," the CDC researchers write. "This effect likely is mediated through reduced second-hand-smoke exposure among nonsmokers and reduced smoking, with the former making the larger contribution," they add.

Data on MI hospitalizations were drawn from electronic Colorado Hospital Association administrative data. These data included admission date, primary diagnosis code, sex, age, residential zip code, and hospital name. No other patient-level data, including smoking status, were available. To examine whether the MI-rate change could be attributable to preexisting secular trends, the researchers looked at MI rates for all three sites for three 18-month periods preceding the preimplementation phase and found no statistically significant secular trend.

To ensure that the rate change was not attributable to undercounting fatal MIs postimplementation, the researchers obtained the number of MI deaths for the city. After accounting for MI deaths by assuming that all fatal MIs occurred in patients who failed to reach the hospital and adding these numbers to the hospital MI admission data, the researchers found that the relative risk for the city of Pueblo was still statistically significant, at 0.82 from the phase 2 to phase 1 postimplementation periods and at 0.66 from phase 2 postimplementation to the preimplementation period.

An editorial note points out that in addition to reducing smoking in public places, smoke-free laws are associated with increased adoption of no-smoking rules in private homes and have also been found to prompt some smokers to quit smoking. It suggests that the continued decrease in MI hospitalizations observed in this study might be a result of a combination of the reduction in second-hand-smoke exposure among nonsmokers in public places, further reductions in second-hand-smoke exposure from more smoke-free homes over time, and more smokers quitting as a result of the smoke-free law and associated changes in social acceptance.

The authors note that in addition to this study, eight other published studies have reported that smoke-free laws were associated with rapid, considerable reductions in hospitalizations for MI. But they add, "The current study adds to the previous evidence by documenting this effect in a relatively large population and by demonstrating that the effect was sustained over an extended period." A meta-analysis of seven of the previous eight studies and one unpublished study yielded a collective estimate of a 19% reduction in MI hospitalization rates after implementation of smoke-free laws, and three studies have suggested that these reductions are more pronounced among nonsmokers than among smokers, they report.

"These findings provide support for considering smoke-free policies an important component of interventions to prevent heart-disease morbidity and mortality," the authors conclude.