The rate of myocardial infarction dropped by one-third after laws prohibiting smoking in public places and workplaces were enacted in Olmsted County, Minnesota, according to a report published online Oct. 29 in Archives of Internal Medicine.
Although this epidemiologic study could not establish causality, no other interventions during the study period could plausibly explain this community-wide reduction in the MI rate. And the only major MI risk factor that declined concurrently was the prevalence of smoking; rates of hypertension and hypercholesterolemia remained steady, and rates of diabetes and obesity increased, said Dr. Richard D. Hurt of the Nicotine Dependence Center and the department of internal medicine at the Mayo Clinic in Rochester, Minn., and his associates.
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Several studies have shown that smoke-free laws lead to a reduction in myocardial infarctions.
"We believe that secondhand smoke should be considered a major risk factor for MI, joining family history, hypertension, hyperlipidemia, diabetes mellitus, and low physical activity. Hence, all clinicians should ascertain secondhand smoke exposure and promote the elimination of secondhand smoke exposure as part of their lifestyle recommendations," they noted.
"All people should avoid secondhand smoke exposure as much as possible, and those with [coronary heart disease] should have no exposure to secondhand smoke," the investigators added.
Several studies have documented declines in hospital admissions for MI after the implementation of smoke-free laws, and the Institute of Medicine has concluded that there is a causal relationship between smoking bans and reductions in acute coronary events. To more closely examine the magnitude of that risk reduction, Dr. Hurt and his colleagues analyzed data from the Rochester Epidemiology Project, in which all cases of MI and sudden cardiac death in a well-defined community were validated using rigorous epidemiologic criteria. This project "has a long track record (more than 50 years) of robust epidemiologic studies," they said.
In Olmsted County, restaurants were required to be smoke free as of Jan. 1, 2002; bars and workplaces were required to follow suit on Oct. 1, 2007. The researchers examined rates of MI and sudden cardiac death during the 18 months before and the 18 months following implementation of each ordinance.
During the entire study period, there were 717 incident MIs and 514 cases of sudden cardiac death.
The age- and sex-adjusted rate of MI dropped from 150.8/100,000 people before the laws were implemented to 100.7/100,000 afterward – a 34% decline, the investigators said (Arch. Intern. Med. 2012 [doi:10.1001/2013.jamainternmed.46]).
Similarly, there was a 17% decline in the incidence of sudden cardiac death during this period, which indicates a trend but does not constitute a statistically significant reduction.
Smoke-free legislation is effective not only because it decreases the amount of secondhand smoke to which nonsmokers are exposed, but also because it reduces the intensity of smoking among smokers, increases quit rates, and reduces the rate of taking up smoking in the first place, Dr. Hurt and his associates said.
Other research has demonstrated that as little as 30 minutes of exposure to secondhand smoke causes an abrupt and dramatic decrease in coronary artery flow velocity reserves and vascular injury that inhibits endothelial function. Exposure also has been associated with low HDL cholesterol levels, increased markers of inflammation, increased serum levels of fibrinogen and homocysteine, decreased antioxidant levels, and increased insulin resistance, they wrote.
Taken together, these findings indicate that physicians should "become advocates for effective tobacco control policies, such as increased taxes, graphic labeling, smoke-free workplaces, and marketing and advertising restrictions," the researchers said.
One limitation of this study was that the population of Olmsted County is predominantly white. Further studies are needed "in communities of more diverse racial and ethnic composition," Dr. Hurt and his colleagues said.
This study was supported by ClearWay Minnesota; the National Heart, Lung, and Blood Institute; and the National Institute on Aging. No financial conflicts of interest were reported.