After thinking some more about the Iceland smoking ban/heart attack study, I feel obligated to comment further on the poor quality of the science of this study, not only because it invalidates the conclusion of this particular study, but because it demonstrates a striking bias that is present in all of the studies of this type and therefore has implications for evaluating the entire field of research in this area.
It turns out that the Iceland study was the topic of a poster presentation at the NBCC conference in June (see abstract P053). Here are the details of the study:
"Introduction: Possible effects of a smoking ban in public places on the incidence of acute coronary syndrome (ACS) are unknown. We hypothesised that such a ban would decrease the incidence of ACS among non-smokers in Iceland.
Material and methods: Nationwide data was gathered prospectively on all patients that underwent coronary angiography for ACS during the 5 months prior to and following the smoking ban. Current smokers were excluded. ACS was defined as: clinical symptoms of unstable coronary artery disease (chest pain at rest) as well as at least one of the following 1) elevated cardiac enzymes, 2) ischemic changes on the EKG at rest, or 3) an abnormal exercise stress test during the same unstable episode.
Results: Totally 378 patients were included in the study. Males were 281 and females 97 (p<0.01). Women were 24% vs. 28%, hypertensive’s 54% vs. 65%, former smokers 65% vs. 67%, 57% vs. 56% were on statin therapy, and 16% vs. 16% had diabetes before and after the ban, respectively (p=ns for all). Among men a 21% reduction of the ACS incidence was seen during the 5 months following (n=124), compared to the 5 months prior to (n=157) the ban (p<0.05). In the total population a trend was seen towards a 17% reduction in ACS (p=0.08). No effect was seen among women (0.5%, p=ns).
Conclusions: A significant 21% reduction in the incidence of ACS was seen among non-smoking men, but not among women, after a smoking ban in public places became effective in Iceland."
The Rest of the Story
Like the abstract presented at the European Society of Cardiology conference earlier this month, this abstract does not mention the date (month and year) in which the smoking ban was implemented in Iceland. Given that this study examined only five months prior to and five months after the smoking ban, it seems quite important for the abstract to reveal the specific months that were included in the study.
Why? Because there is a well-recognized seasonal variation in acute coronary syndrome, with peak incidence during the winter months, high incidence during the spring and the lowest incidence during the summer. This is recognized in the literature as a universal phenomenon (see Cheng TO. Seasonal variation in acute myocardial infarction. International Journal of Cardiology 2009; 135:277-279).
Cheng explains the reasons for this observation: "Cold temperature in the winter can cause increased cardiac workload, higher coronary and vascular resistance, higher blood pressure and higher fibrinogen levels, all of which are conducive to acute myocardial infarction. That it is the colder environmental temperature in the winter in most parts of the world rather than the winter season per se that is the principal reason for increased hospital admissions for acute myocardial infarction is evidenced by the observation that the peak month of acute myocardial infarction admitted to hospitals in Melbourne, Australia was July, which is the coldest month of the year."
Given this seasonal variation in heart attacks, I was surprised to find out that the smoking ban in Iceland went into effect on June 1, 2007. This means that the pre-ban period included the months of January, February, March, April, and May. And the post-ban period included the months of June, July, August, September, and October.
The average temperatures (degrees Centigrade) during the pre-ban months in Reykjavik are: 1.9, 2.8, 3.2, 5.7, and 9.4. The average temperatures during the post-ban months are: 11.7, 13.3, 13.0, 10.1, and 6.8.
Thus, based on seasonal variation alone, one would expect to observe a much lower incidence of acute coronary syndrome in Iceland during the period of June through October compared with the period of January through May. One would expect acute coronary syndrome incidence to peak in the winter (the pre-ban period), remain high in the spring (also pre-ban period), and to wane in the summer (the post-ban period).
Thus, the study methodology is basically a set-up to detect a reduction in the incidence of acute coronary syndrome. The fact that the abstract reports finding an overall 17% reduction is not at all surprising given the months during which these data were collected. One would expect a 17% reduction based on the seasonal variation alone.
In fact, one of the most comprehensive studies of seasonal variation in acute myocardial infarctions found that there is a 40% reduction in the incidence of heart attacks in the summer compared to the winter and spring (see: Rumana et al. Seasonal pattern of incidence and case fatality of acute myocardial infarction in a Japanese population [from the Takashima AMI Registry, 1988 to 2003]. American Journal of Cardiology 2008; 102: 1307-1311).
Therefore, the study results, as taken from the information provided in the study abstract, do not support a conclusion that the smoking ban had any effect on reducing acute coronary syndrome incidence in Iceland.
But what strikes me, after thinking about this for a few days, is just how bad this science is. I just don't see how any objective scientific study of this issue would fail to account for the seasonal variation in acute coronary syndrome, especially when the post-ban months are precisely those in which one would expect the incidence to go down.
If the same study were conducted by the tobacco industry, we would be blasting the companies for intentionally rigging the study to find their pre-determined conclusion.
I tried to give the study a chance by searching to see whether perhaps it did adjust for seasonal variation but that the adjustment was not apparent. However, when you look at the actual numbers reported, you'll see that there was no adjustment.
The study reports a decline of acute coronary syndrome cases among men from 157 to 124. This is a 21% reduction, which is what the study reports. Thus, the study is simply reporting the percentage decline in the number of cases. There is no adjustment for seasonal variation in acute coronary syndrome incidence.
While I'm not arguing here that the study was intentionally rigged to try to make it look like the smoking ban had an effect, the fact that the study appears to have completely ignored the well-recognized seasonal variation - which in this case is a fatal flaw of the study, completely invalidating the study conclusion - suggests that a very strong bias is present. Unfortunately, I find this to be the case with nearly all of the studies that have been published on this topic of the immediate effects of smoking bans on heart attack incidence.
I understand that researchers in tobacco control very much want there to be an immediate effect of smoking bans on heart attacks. Of course we want to be able to say that our efforts have resulted in an immediate reduction in severe morbidity and mortality. But we cannot and should not abandon rigorous scientific standards to try to show that there is such an effect.