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A six-month ban on smoking in public areas in one US town led to a drop in the number of heart attacks - and the numbers rose again when the ban was lifted. Local politics in Montana have allowed a natural experiment on the effects of passive smoking. In 2002, the isolated town of Helena decided to ban smoking in public areas and workplaces. But six months later, pro-tobacco people overturned the law. So for a half-year window, passive smoking outside the home was regulated. Since several of the effects of smoking on the heart are short-acting, researchers concluded that was long enough to see results with heart attacks. In addition, Helena only had one hospital for heart problems so it was possible to get a fairly accurate idea of what was going on. The results showed that compared to the same six-month period before the smoking ban, admissions to the hospital of people with proven heart attacks fell significantly. And in the same six months the year after the ban was lifted, the numbers bounced back. Not perfect evidence, but strongly suggestive of an effect. But why should low-dose tobacco smoke have an influence? Well, the risk attached to smoking seems to rise very rapidly with small numbers of cigarettes then evens out. Anyway it's more reason to expect healthy air when you go out for a drink or meal.
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