Does passive smoking kill 600,000 people every year?

Question

While reading David Nutt's book on the harms caused by legal and illegal drugs and how to minimise them (Drugs without the hot air), I came across a claim which reminded me of some previous questions on passive smoking here (for example this question Is secondhand smoke dangerous?).

The claim is that passive smoking kills 600,000 people every year. This specific claim seems to have been widely circulated but the reference in Nutt's book is to a WHO summary report which itself does not reference any studies. But it seems to have been repeated many times.

The general question about passive smoking is fairly well addressed in previous answers. But I'm more interested in this very specific claim. Is is based on some published analysis? Is that specific analysis credible? Or has it gained widespread attention because it fits with the consensus rather than because it is a credible, well argued result?*

Answer 1

The 600,000 figure seems to have come from "Worldwide burden of disease from exposure to second-hand smoke: a retrospective analysis of data from 192 countries" by Mattias Öberg and others published in The Lancet, Volume 377, Issue 9760, Pages 139 - 146, 8 January 2011 and online 26 November 2010, which said "603 000 deaths were attributable to second-hand smoke in 2004." It also said

The calculations were based on disease-specific relative risk estimates and area-specific estimates of the proportion of people exposed to second-hand smoke, by comparative risk assessment methods, with data from 192 countries during 2004.

So if you accept the particular relative risks from exposure to second-hand smoke adopted by the article, and accept the rates of exposure in the different countries considered, then you should accept the total figure as being reasonable.

If you don't accept these relative risks (i.e. the more general question you point to), then you probably will not accept the total figure from this analysis.

Answer 2

According to the literature, cigarette mainstream smoke (MS) essentially increases the risk of two major groups of life threatening diseases: Cancer and Cardiovascular diseases.

The assessment that Environmental Tobacco Smoke (ETS) exposure should cause similar effects is a logic deduction, albeit theoric but epidemiologic data is controversial, at best.

Since Cardiovascular Dieses are multifactorial and poor targets for comparison, most studies use Cancer (Lung Carcinoma specially) for comparison.

From the papers I had the opportunity to review, most are biased or are statistically weak.

Here's some excerpts from Review Articles in the subject with the respective source:

A significant part of an association between lung cancer and exposure to ETS would disappear, if, on the average, 1 patient out of 20 nonsmoking cases had failed to tell the interviewer that he had, in fact, recently stopped smoking.

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The fact that the mutation spectrum of the p53 tumor suppressor gene in lung tumors of ETS-exposed nonsmokers generally differs from that found in tumors of active smokers lends additional support to the notion that the majority of tumors found in ETS-exposed nonsmokers have nothing to do with tobacco smoke.

http://www.ncbi.nlm.nih.gov/pubmed/11726024

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The average intake of toxic and genotoxic compounds due to ETS exposure is that low that it is difficult, if not impossible, to explain the increased risk of lung cancer as found in epidemiological studies. The uncertainty is further increased because the validity of epidemiological studies on passive smoking is limited severely by numerous bias and confounding factors which cannot be controlled for reliability. The question of whether or not ETS exposure is high enough to induce and/or promote the carcinogenic effects observed in epidemiological studies thus remains open, and the assumption of an increased risk of lung cancer due to ETS exposure is, at present, more a matter of opinion than of firm scientific evidence.

http://www.ncbi.nlm.nih.gov/pubmed/11401014

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My point is: If the claim that ETS increases death risk is controversial and no large scale studies could have possibly been conducted, this number is, quite possibly at best, an abusive statistical deduction.

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SIDENOTE: Here's, for comparison, a interesting study regarding Air Pollution exposure:

http://www.ncbi.nlm.nih.gov/pubmed/19554969