Has it really been a whole year? The longer I blog, the faster time seems to fly. Or maybe it’s just because I’m getting older. Whatever the case, you may (or may not) recall that about a year ago I got into a little tussle with a certain Libertarian comic and some smoking cranks over the issue of whether secondhand smoke is a health threat. The discussion escalated a bit, and some serious smoking cranks entered the fray, complete with quote-mining. I ended up discussing a couple of studies that claimed to have found a decrease in hospital admissions for acute coronary syndrome (colloquially known as heart attacks) in the months after the enactment of smoke-free workplace laws, one in Helena, MT in particular. These studies all had a lot of shortcomings, so much so that they made it too easy for those opposed to smoke free workplace laws to dismiss them.
And, so, after a flurry of posts about this topic that ended, ironically enough, exactly one year ago today, I more or less let the topic drop.
What should I find in the latest, crispy issue of the New England Journal of Medicine but a large study from Scotland looking at the very same issue that avoids most of the flaws in the previous studies. The study, from the University of Glasgow and the University of Edinburgh, comes to the same conclusion: that the implementation of a smoke free workplace law resulted in a rapid and significant decrease in admissions for acute coronary syndrome, 17% to be precise.
One of the biggest (and most valid) criticisms of the Helena, MT and Pueblo, CO studies before, which are the two studies that I’m familiar with that showed a drop in such admissions after the implementation of smoke free workplace laws was that they were retrospective studies and thus prone to all the numerous possible confounding factors. Another valid criticism is that these studies often didn’t cover a large enough geographic area or include enough patients to minimize the effect of having their cachement area include communities that did not have similar smoking bans.
The present Scottish study is the largest and most rigorous study thus far done examining the hypothesis that the enactment of workplace smoking bans, including restaurants and bars, results in a decrease in admissions for acute coronary syndrome (ACS). Scotland has a population of 5.1 million, and there were nine hospitals studied, which made up 63% of the admissions for cardiac disease during the time period studied. Most importantly, the authors prospectively studied hospital admissions for acute coronary syndrome. I can’t emphasize how important this is. Prospective studies may be prone to confounders, but the number of potential confounders increases exponentially for a retrospective study to the point where it’s impossible to control for them all. Also, the criteria for case ascertainment used to define whether a patient had an admitting diagnosis of acute coronary syndrome were rigorously defined. In addition, smokers and nonsmokers were stratified, and it was verified that nonsmokers’ reports of secondhand smoke exposure correlated with serum cotinine levels. (Cotinine is a metabolite of nicotine that is often used to evaluate and quantify exposure to tobacco smoke.)
Investigators then examined hospital admissions for acute coronary syndrome for the ten months before the enactment of a smoke free workplace law at the end of March 2006 and the ten months after. Month-by-month comparisons were made in order to control for seasonal variations in the number of admissions for acute coronary syndrome. Finally, to account for unrelated changes in lifestyle or treatment changes,the historical trend in admissions in Scotland was compared with contemporaneous data from England. The reason for this was to make sure, as much as possible, that a preexisting downward trend in such admissions didn’t confound the results.
Once the data were collected and the numbers crunched, the result showed that admissions for acute coronary syndrome decreased by 17% in the period after enactment of the law. Even more striking, there was a decrease each month that tended to be more pronounced as time when on, as demonstrated in this graph:
Patients admitted for acute coronary syndrome were prospectively questioned and blood samples taken from them for cotinine levels, allowing investigators to determine that two-thirds of the decline in admissions was attributable to nonsmokers or former smokers, strongly suggesting that decreased exposure to secondhand smoke was responsible for the decline. Because of its size and rigorous design, this study represents some of the strongest evidence yet supporting the hypothesis that enacting workplace smoking bans results in decreased numbers of admissions for ACS. It also is consistent with the results of the much-maligned Helena and Pueblo studies, which, despite their retrospective nature and many flaws, appear to have been mostly confirmed and supported by the Scottish study. A Medpage Today story summarizes additional results quite well; so I’m going to quote from it, rather than reinventing the wheel and summarizing myself:
Remarkably, Dr. Pell and colleagues found that non-smokers appeared to benefit significantly more than current smokers.
Among the latter, admissions fell 14% (95% CI 12% to 16%) after the ban, whereas among those who had never smoked, they declined 21% (95% CI 18% to 24%).
The decline in admissions was also greater among former smokers (down 19%, 95% CI 17% to 21%).
The researchers found significant differences along age and gender lines.
Women appeared to have benefited from the ban more than men. For example, among those who never smoked, the decline in admissions reached 28% in women (95% CI 23% to 33%), whereas for men the decline was only 13% (95% CI 9% to 17%).
The researchers said this result may reflect the increased risk from smoking to women relative to men. When they reduce exposure to smoke, women may therefore benefit disproportionately as well.
Likewise, older people — men over 55 and women over 65 — appeared to benefit more than younger individuals. For non-smoking men 55 or younger, admissions for acute coronary syndrome did not decrease significantly at all.
Dr. Pell and colleagues noted that in England, which did not implement a smoking ban during the same period, hospital admissions for acute coronary syndrome declined by 4% and there was a mean annual decrease of 3% in Scotland during the decade preceding the study.
Another excellent summary of this trial can be found here.
The obvious caveat about this study is, of course, that correlation does not necessarily equal causation. However, when a study is done rigorously enough and with adequate controls for confounding factors, correlation can be highly suggestive of causation, and this is the case here. There is a close temporal correlation between the drop in hospital admissions and a single change in public policy. No other major change that could account for such a dramatic drop occurred during the same time period, and a very similar population on the same island demonstrated no such decrease, which was dramatically more pronounced than the 3-4% per year trend in decreases. Add to that the methodologically rigorous manner in which smoking history, exposure to secondhand smoke, and serum cotinine levels were measured, ant this study is very persuasive evidence suggesting that smoking bans of this sort have a rapid and dramatic effect on public health.
Indeed, by any measure, this is amazing stuff. Even I was skeptical that results this striking could result from such a simple public health measure, given the sometimes difficult to quantify health risks due to secondhand smoke. Moreover, this study demonstrated that, among nonsmokers and former smokers, cotinine levels fell significantly, and the percentage of people who had never smoked who reported no exposure to second-hand smoke increased from 57% to 78%, an increase largely attributable to reduced exposure to smoke in bars, restaurants, clubs, and pubs. There was a component of decreased smoking among current smokers, as well. In the three months leading up to the ban, there was a 67% increase in calls to smoking cessation hotlines. Clearly some people were using the ban as an impetus at least to try to quit smoking, and even if they failed they generally did cut back for a while at least.
Of course, I have no illusions that the resistance to such smoking bans in the workplace will go away after this study. Such resistance is primarily based on ideology rather than science, and I can to some extent understand and partially sympathize with the view that restaurant and bar owners should be free to allow or ban smoking as they please. On the other hand, the libertarian argument that restaurants or bars should be free of such regulation is in marked contrast to the acceptance of routine public health laws. Restaurants and bars are heavily regulated to begin with because of their very nature and how easily slackness in food handling and preparation can endanger public health, and no one would argue against such regulations. Now evidence is now mounting that allowing smoking in public restaurants and bars is similarly a health hazard; it is not unreasonable to consider regulating it as well to prevent health problems attributable to secondhand smoke.
It is also true that there is the tendency to go too far with such bans. For example, smoking bans at outdoor venues have nothing that I can tell to do with protecting public health and lots to do moralizing or “setting an example.” Indeed, my campus recently went smoke-free everywhere–including outdoors–and that was almost explicitly part of the rationale. It’s one of the dumbest things I’ve seen; smoking is banned anywhere on university property. However, evidence is accumulating that indoor workplace smoking bans have beneficial effects. The current Scottish study represents the latest and the strongest current evidence suggesting significant public health benefits in communities in which indoor smoking in public places is banned. It represents yet one more nail in the coffin of the argument that secondhand smoke is harmless or that there is not a tradeoff for permitting it. Given that, I expect that it won’t take long at all for a a concerted attack on these investigators and their study to be launched, if one hasn’t been launched already.
Pell, J.P., Haw, S., Cobbe, S., Newby, D.E., Pell, A.C., Fischbacher, C., McConnachie, A., Pringle, S., Murdoch, D., et al. (2008). Smoke-free Legislation and Hospitalizations for Acute Coronary Syndrome. New England Journal of Medicine, 359(5), 482-491.