Cardiac Health of Nonsmokers Improved By Smoke-Free Laws

Diedtra Henderson

October 30, 2012

People around the world living in communities that have enacted smoke-free legislation have lower risks of suffering smoking-related cardiac, cerebrovascular, and respiratory diseases. Furthermore, the tougher the new laws, the more dramatic the risk reduction, according to a meta-analysis by Crystal E. Tan, MS, from the Center for Tobacco Control Research and Education at the University of California, San Francisco, and Sharon A. Glantz, PhD, from the Department of Medicine, University of California, San Francisco.

A second study, led by Richard D. Hurt, MD, from the Nicotine Dependence Center and the Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota, found a 33% decline in myocardial infarction (MI) after all workplaces in Olmsted County Minnesota became smoke-free.

The analysis by Tan and Dr. Glantz was reported in an article published in the October 30 issue of Circulation. The research led by Dr. Hurt was reported in an article published online October 29 in the Archives of Internal Medicine.

Secondhand smoke causes cardiovascular and respiratory disease in adults, impairs reproductive outcomes for women, and delays children's growth, Tan and Dr. Glantz found. In addition, the health effects of secondhand smoke can be more severe for nonsmokers, Dr. Hurt and coauthors found, with cardiovascular harm nearly as significant as that suffered by active smokers. An estimated 46,000 Americans who are nonsmokers die each year from cardiovascular events related to secondhand smoke, Dr. Hurt and colleagues write.

Wave of Legislation

In recent years a wave of legislation has swept across the United States and other countries imposing limits on smoking in workplaces, restaurants, and bars reducing nonsmokers' exposure to secondhand smoke. Decreases in hospitalizations and deaths from cardiovascular and respiratory disease followed.

In the first study, Tan and Dr. Glantz sought to determine the relationship between smoke-free legislation and hospital admission or death from cardiac, cerebrovascular, and respiratory diseases. They searched for studies published before November 30, 2011, and included 45 studies of 33 smoke-free laws with a median follow-up of 24 months. The excluded studies included a single tobacco industry–supported paper that was underpowered and failed to fully factor in the effect of legislation in California and New York.

"Comprehensive smokefree legislation was associated with significantly lower rates of hospital admissions (or deaths) for all 4 diagnostic groups: coronary events (RR [relative risk] .848, 95% CI [confidence interval] .816-.881), other heart disease (RR .610, 95% CI, .440-.847), cerebrovascular accidents (RR .840, 95% CI .753-.936), and respiratory disease (RR .760, 95% CI .682-.846)," the authors write.

"There was an overall pattern of more comprehensive laws being associated with greater reductions in hospital admissions (p=.001 for individual outcomes...and p=.002 for disease groups)," they continue.

The researchers also found that comprehensive smoke-free laws were associated with a 15% reduction in hospitalizations for acute MIs (AMIs), mirroring the significant decreases in AMI found in earlier meta-analyses. However, unlike in earlier studies, the researchers did not find that reductions in risk increased with longer follow-up.

Tan and Dr. Glantz caution that the legislation itself does not produce the observed effects and, instead, credit the reduction in exposure to secondhand smoke and the increases in smoking cessation that accompany such laws.

Causal Link?

The authors acknowledge that the interrupted time series observational studies included in their meta-analysis do not establish causation. However, in Helena, Montana, hospitalizations for AMI rebounded after its smoke-free law was suspended, supporting a causal link, the authors write. Other limitations include the fact that few studies in the group actually measured tobacco smoke exposure or individual smoking status.

"This study provides evidence that smokefree laws are followed by fewer hospitalizations and lower health care expenditures for a wide range of diseases and that comprehensive laws ending smoking in workplaces, restaurants, and bars are associated with greater effects," the authors conclude. "The general public, public health professionals, and policy makers should consider these positive associations as they develop smokefree legislation and decide whether or not to include exceptions to these laws."

In the second study, Dr. Hurt and coauthors sought to tease out the effect of smoke-free legislation on population health in Olmsted County in Minnesota. In 2002, the county implemented an ordinance that made restaurants smoke-free. In 2007, the smoke-free mandate was expanded to all workplaces, including bars.

The researchers relied on the Rochester Epidemiology Project to measure the incidence of MI and sudden cardiac death (SCD), defined as an out-of-hospital death associated with coronary disease, 18 months before and after implementation of each smoke-free ordinance. They adjusted for age and sex in their multivariable analysis.

"Over the entire study period comparing 18 months before Ordinance 1 and 18 months after Ordinance 2, we observed a 33% decline in the incidence of MI (adjusted RR, 0.67; 95% CI, 0.53-0.83; P = .001)," the researchers report. "There was a 17% decline in the incidence of SCD for the overall study period comparing the 18 months before Ordinance 1 with the 18 months after Ordinance 2 (adjusted RR, 0.83; 95% CI, 0.65-1.06; P = .13)."

Although misclassification of death can occur in death certificates, the authors say the temporal trends they studied were unlikely to be confounded by death classifications. The Minnesota study reflects the experience of a primarily white study population; the authors suggest further studies in communities that are more racially and ethnically diverse. They point to the rigor of the Rochester Epidemiology Project and their validation of all MI and SCD cases using rigorous epidemiologic criteria as among the study's strengths.

"The implementation of smoke-free workplace ordinances was associated with a substantial decrease in MI, the magnitude of which is not explained by concomitant community interventions or changes in cardiovascular risk factors, with the exception of smoking prevalence," the authors conclude. "Exposure to [secondhand smoke] should be considered a modifiable risk factor for MI."

The National Cancer Institute provided funding for Tan's study. ClearWay Minnesota provided funding for Dr. Hurt; the National Heart, Lung, and Blood Institute/National Institutes of Health provided funding for one coauthor; and the National Institute on Aging/National Institutes of Health provided funding for the Rochester Epidemiology Project. The other authors have disclosed no relevant financial relationships.

Circulation. 2012;126:2177-2183. Full text

Arch Intern Med. Published online October 29, 2012. Abstract