Heart Attacks and the Massachusetts Smoking Ban

Last week the Massachusetts Department of Public Health claimed a new study shows the state's smoking ban has resulted in 577 fewer heart attack deaths per year since it took effect in July 2004. The department, perhaps hoping its spin will be accepted before critics have a chance to examine the basis for it in detail, does not plan to release the study until next year. All we have to go on is a press release, a "fact sheet" (PDF), and a story in The Boston Globe. But several things are clear:

1) Heart attack deaths were already declining before the statewide ban; the researchers claim the trend accelerated after the law took effect.

2) Judging from the graph on the fact sheet, heart attack deaths (as a percentage of all deaths) fell sharply after the ban even in municipalities that were already subject to local smoking bans, including those that had "strong" laws. That's not what you'd expect if restrictions on smoking caused the decline.

3) The reduction in heart attack deaths reported by the Globe—30 percent over three years—is much smaller than  the effects attributed to smoking bans in other studies. The report on Helena, Montana, for example, initially claimed a 60 percent reduction in heart attacks within six months, which was later downgraded to 40 percent.

4) Although Massachusetts Public Health Commissioner John Auerbach says "we believe the single most compelling reason [for the decline in heart attacks after the ban] was reduced exposure to secondhand smoke in workplaces," it's not clear what biological mechanism would account for such a quick effect. It can't be that fewer people are developing heart disease, since that takes years. Presumably what Auerbach has in mind is that less secondhand smoke means heart attacks are less likely to be triggered in people with pre-existing heart disease. Is there any evidence that, prior to the ban, nonsmokers with heart disease were keeling over dead as a result of heart attacks triggered by exposure to secondhand smoke?

Michael Siegel, who seems to have had a look at the raw data, has more (emphasis added):

In the first year after the smoking ban was implemented, there was no significant decline in heart attack deaths in the state. Moreover, there was no decline in heart attack deaths even among just those residents living in towns that did not previously have smoking bans. Thus, this study refutes the conclusions from Helena, Pueblo, Bowling Green, etc. that smoking bans immediately reduce heart attacks by decreasing secondhand smoke exposure.

The study did find a decline in heart attack rates from the first to second year after the statewide smoke-free law was implemented, but it turns out that the magnitude of this decline was not significantly different in towns with or without smoking bans prior to the state law. Thus, the study provides no evidence that the statewide smoking ban was associated with any significant decline in heart attacks, even up to two years after its implementation.

Siegel adds that cities with smoking bans did see significant reductions in heart attack deaths compared to cities without such laws in the seven-year period from 1999 through 2006. They also had lower smoking rates, which suggests they may be seeing the results of improving health in former smokers who quit as a result of the ordinances. Case-control studies indicate that the heart disease rate among former smokers falls by about 50 percent within four years of quitting.

In short, even if secondhand smoke has no measurable impact on death rates, over the long term smoking bans can be expected to reduce the incidence of heart disease (and other smoking-related illnesses) by pressuring smokers to quit. From a "public health" perspective, in fact, that is the main benefit of smoking bans. But whether we're talking about smokers or nonsmokers, immediate, sharp reductions (within the first six months to a year) are not biologically plausible, and they're not what the Massachusetts study found.