Tuesday, 23 November 2010

Second-hand smoke

While some worry about third-hand smoke, we can't even be sure that second hand smoke has detrimental effects. From BMC Cancer (DOI):
ETS exposure was not found to significantly increase risk among never smokers in this study, however, several potential explanations are possible. ETS exposure either as a child or an adult in the home or the workplace has been evaluated in numerous studies [53]. The results, however, have been inconsistent as to the significance and magnitude of the effects among never smokers. When estimates were pooled in a meta-analysis of 34 case-control studies of non-smokers, a pooled relative risk of 1.2 (95% CI 1.1-1.4) was observed, although only seven out of 34 studies reporting significantly elevated risk [6]. It was suggested that the inconsistency in the significance of findings across studies could be due to issues of sample size, measurement error, recall bias and confounding [54]. Despite our efforts to minimize misclassification bias by collecting data on involuntary tobacco smoke exposure data for home, work and other exposure locations during both childhood and adulthood, the possibility of these issues cannot be excluded.
They do find exposure to welding equipment, solvents & paints, and soot/woodsmoke are associated with increased risk of lung cancer. But not environmental tobacco smoke. There doesn't seem to be nearly as much handwringing about any of the other findings as there is about the failure to find an effect of ETS.

To the extent that we really really care about the harms to which workers expose themselves in the workplace, we should have moved to ban workplace exposure to welding equipment and paints before banning smoking in bars and restaurants. Or require that welding shops and panelbeaters have air ventilation systems more powerful than those that were required in restaurants back when they were allowed to have non-smoking sections.

Surprisingly, playing in the shop with the welder when I was a kid has increased my chances of lung cancer by more than did my parents' smoking. Not that I regret having played with the welder. Few things are more worthwhile for a boy than messing about with welders....

Update: Do read Church of Rationality on this one - very nice analysis.


  1. "Not that I regret having played with the welder. Few things are more worthwhile for a boy than messing about with welders"

    Oooh, matron. ;)

  2. Once a lobby group gets a foothold, it is pretty hard to argue against even in the face of solid evidence.

    Great blog by the way

  3. No doubt the MOH will dismiss this as some tobacco industry plot and completely ignore the facts because it doesn't support their efforts.

    God leaving public health up to the officials in the MOH leaves me cold and feeling ill.

  4. Sure, this study chalks one against ETS being a significant cancer risk, but a) it doesn't mean this study is any *more* conclusive than any of the other studies that came before it, and b) the policy consequences isn't based on health risks alone.

    For example, the number of workers in hospitality vs the number of workers in environments involving these industrial processes/chemicals, the viability and cost of eliminating these harmful substances (no smoking vs no welding), etc.

    Out of interest, would your position change at all if the next study comes out claiming that ETS is a significant risk factor? Can you imagine what it would take to change your mind?

    I've been pondering that a lot lately - how, if at all, statistical evidence can change someone's firmly-held position.

  5. @Keith: check the metastudy analysis LemmusLemmus links above.

    Tobacco smoke is carcinogenic. It could be the case that second hand smoke exposure provides sufficient dose to raise the relative risk of cancer. One nice thing in the method above is that it separates never smokers from former smokers: it's harder to disentangle the effects of second hand smoke when nonsmokers and former smokers are lumped together. On the other hand, it's a design protocol with which I'm less familiar: they basically match a bunch of cancer patients with non-cancer folks on a bunch of factors other than smoking.

    My very cursory review of the second hand smoke lit has me worried about a lot of the same kinds of things that worried the J-curve skeptics in the early 1990s: confounding of the comparison sample by mixing never and former smokers; failure to adjust for other health-related behaviours that correlate with smoking status. Those things have been sorted out in the alcohol literature, but I can't see that they have been in the second hand smoke literature. And that makes me less confident in the results of metastudies in that area than I am in the J-curve.

    I've no ideological or other commitments to that there's no effect of second hand smoke, if that's the question. As far as optimal policy goes, I reckon it's invariant to whether second hand smoke is mildly carcinogenic or not: property rights allowing bar, restaurant, or workplace owners to make the decision is sufficient. I'm confident that there isn't a positive effect of second hand smoke; I'm not confident about whether there's zero or a mild negative effect.