According to a study published this month in the Journal of Drug Education, the smoking ban enacted in Monroe County, Indiana in August 2003 has led to a 70% decline in heart attacks among nonsmokers with no previous history of cardiac disease (see: Seo D-C, Torabi MR. Reduced admissions for acute myocardial infarction associated with a public smoking ban: Matched controlled study. Journal of Drug Education 2007; 37:217-226).
The study compared the number of heart attacks among patients without prior cardiac disease or major cardiac risk factors in Monroe County with the number of heart attacks among similar patients in Delaware County, a county in Indiana with similar demographics but no smoking ban. The data were compared for a 22 month period prior to the ban (August 2001 through May 2003) and a 22 month period following the ban (August 2003 through May 2005). The smoking ban was implemented in August 2003 and included all workplaces and restaurants. Bars were initially exempt, but became smoke-free in January 2005. Analysis was stratified by smoking status of the heart attack patients.
The paper reports a 70% decline in heart attacks among nonsmoking patients in Monroe County, compared to only an 11% decline in heart attacks among nonsmoking patients in Delaware County. There was no significant change in heart attacks among smoking patients in either county.
The authors conclude that the substantial reduction in observed heart attacks in Monroe County was attributable to the smoking ban.
In a press release issued by Indiana University to accompany the publication of the study, the authors claim that: "Exposure to second-hand smoke for just 30 minutes can rapidly increase a person's risk for heart attack, even if they have no risk factors. The smoke, which contains carbon monoxide, causes blood vessels to constrict and reduces the amount of oxygen that can be transported in the blood."
The Rest of the Story
To be blunt, this study is crappy and its conclusions are completely invalid. This study would never have passed scrutiny with me had I been asked to review it.
In fact, the results of the study fail to support the paper's conclusion.
While the press release sounds quite impressive, if you take the time to read the actual study, you'll find that the sweeping conclusion that a smoking ban reduced heart attacks among nonsmokers by 70% is based on a total of only 22 heart attacks. That's right. There were only 22 heart attacks among nonsmoking patients in Monroe County in this study between August 2001 and May 2005. And there were only 15 heart attacks among smoking patients in Monroe county during the study period.
The sample size of the study is so small that it is ridiculous to conclude that the observed decline from 17 heart attacks (2001-2003) to 5 heart attacks (2003-2005) was attributable to the smoking ban. With sample sizes this small, the variation in the number of annual heart attacks is expected to be enormous. There is no way that the study can determine that the observed decline was due to the smoking ban, rather than simply to random variation in the number of heart attacks in this small geographic area (only one hospital was included in the study).
More importantly perhaps, if you look at the results, you'll see that there is no significant difference between the change in heart attacks in Monroe versus Delaware counties over the study period. The confidence intervals around the estimates of the change in heart attacks in the two counties overlap widely. Based on the reported confidence intervals, the decline in heart attacks in Monroe County could be as low as 3, and the decline in heart attacks in Delaware County could be as high as 13. In other words, it is entirely plausible, based on the study findings, that the decline in heart attacks in Delaware County was greater than that in Monroe County.
These results make it clear that there is no significant difference in the change in heart attacks between the two counties over the study period, thus nullifying the study conclusion.
I honestly have no idea how something like this managed to get through the peer review process and into publication. But it really doesn't matter. The point is -- the study clearly does not provide support for the conclusion that the smoking ban in Delaware County resulted in a 70% decline in heart attacks among nonsmokers.
There are two other severe problems with the study which deserve mention (as if the above weren't enough).
First, only one hospital was included in the study. It was assumed that all heart attacks suffered by patients living in Monroe County would be picked up at Bloomington Hospital. This is not a fair assumption, however. People travel and if a heart attack occurred while traveling, a person would not present at Bloomington Hospital. Normally, this would not be a problem. But with so small a number of total heart attacks, even if one or two people had heart attacks while away from Bloomington, this would render the study results invalid.
Second, the study excluded patients with a prior history of cardiac disease and those with risk factors for heart disease (such as high cholesterol and hypertension). However, these would be the precise patients among whom a decline in heart attacks attributable to a smoking ban might be expected. This exclusion makes no sense.
The rest of the story is that this study is another example of the junk science that passes muster these days in tobacco control research. It seems that studies which report a decline in heart attacks associated with smoking bans have an automatic green light, regardless of their scientific merit.
But the most unfortunate part of this story is that the press release contains the same fallacious statement that is being made by more than 100 anti-smoking groups. Without any evidence to support it, the press release claims that 30 minutes of secondhand smoke exposure rapidly increases a person's risk of a heart attack even if that person is otherwise healthy (they have no risk factors for heart disease). In fact, the press release offers an explanation for the increased risk -- as if it has already been proven to be the case. The explanation is that the carbon monoxide causes blood vessels to constrict and reduces the amount of oxygen that can be transported in the blood.
Well the truth is that hypoxia (reduced oxygen delivery) alone is not a cause of most heart attacks. You need to have restricted blood flow through the coronary arteries.
More importantly, the truth is that 30 minutes of secondhand smoke has been demonstrated not to cause constriction of the blood vessels supplying blood to the heart. Coronary blood flow was not decreased in subjects who were exposed to secondhand smoke for 30 minutes (see: Otsuka R, Watanabe H, Hirata K, et al. Acute effects of passive smoking on the coronary circulation in healthy young adults. JAMA 2001; 286:436-441).
The press release basically seems to be making this all up as it goes along, all in an apparent effort to support findings that are neither valid nor plausible.