Smoke-Free Workplace Laws and Incidence of MI

Previous studies have documented an association between declines in hospital admissions for myocardial infarction (MI) and implementation of smoke-free legislation. A meta-analysis of 17 published studies found a 10% reduction in admissions for MI in areas where smoke-free workplace laws have been implemented.

According to a committee from the Institute of Medicine, “There is a causal relationship between smoking bans and decreases in coronary events.” However, the committee did not comment on the magnitude of the decrease in relative risk.

In 2002, a smoke-free restaurant ordinance (Ordinance 1) was implemented in Olmsted County, Minnesota, and in 2007, all workplaces, including bars, became smoke-free (Ordinance 2). To evaluate the population effect of implementation of smoke-free laws on cardiovascular events, researchers recently conducted an analysis of data from the Rochester Epidemiology Project, including individual patient data for MI cases validated using epidemiologic criteria and sudden cardiac death (SCD) in Olmsted County before and after the smoke-free laws were implemented.

The researchers reported results of their analysis in Archives of Internal Medicine [2012;172(21):1635-1641].

Potential cases of MI included patients admitted to Olmsted County hospitals with an International Classification of Diseases, Ninth Revision code 410 (acute MI). Validation criteria of infarction included manual data collection of information and use of algorithms combining cardiac pain and electrocardiographic and biomarker data. SCD was defined as out-of-hospital death with the primary cause of death classified as coronary heart disease on the death certificate.

During the 18 months before and after implementation of each smoke-free ordinance, there were 717 incident cases of MI and 514 people who experienced SCD. Characteristics were similar before and after the ordinance periods, with the exception of hyperlipidemia in persons experiencing SCD before and after Ordinance 1 (36.4% vs 54.0%, respectively; P=.004).

For the 18 months before Ordinance 1, the age- and sex-adjusted rate of MI was 150.8 per 100,000 (95% confidence interval [CI], 129.0-172.6). For the 18 months after Ordinance 1, the rate was 144.6 per 100,000 (95% CI, 123.6-165.5); there was no significant decline in the incidence of MI during this period.

For the period before and after Ordinance 2, the incidence of MI adjusted for age and sex declined from 152.3 per 100,000 (95% CI, 131.4-173.3) to 100.7 per 100,000 (95% CI, 83.8-117.5), equating to a 34% decline over the 18 months before and after implementation of the ordinance (adjusted relative risk [RR], 0.66; 95% CI, 0.53-0.82; P<.001). Over the entire study period (comparing 18 months before Ordinance 1 and 18 months after Ordinance 2), there was a 33% decline in the incidence of MI (adjusted RR, 0.67; 95% CI, 0.53-0.83; P<.001).

For the 18 months before and 18 months after implementation of Ordinance 1, there was no significant decline in SCD. In addition, there was no significant change in the rates of SCD 18 months before Ordinance 2 compared with 18 months after Ordinance 2. For the overall study period (18 months before Ordinance 1 through 18 months after Ordinance 2), there was a 17% decline in the incidence of SCD, a nonsignificant change.

The researchers noted that during the overall study period, there was a decline in the prevalence of smoking. The prevalence of hypertension, diabetes mellitus, hypercholesterolemia, and obesity either remained constant or increased during the same time period.

In conclusion, the researchers said, “A substantial decline in the incidence of MI was observed after smoke-free laws were implemented…As trends in other risk factors do not appear explanatory, smoke-free workplace laws seem to be ecologically related to these favorable trends. Secondhand smoke exposure should be considered a modifiable risk factor for MI. All people should avoid secondhand smoke to the extent possible, and people with coronary heart disease should have no exposure to secondhand smoke.”