Smoke free legislation linked to drop in second-hand smoke exposure among adults
Levels of second-hand smoke exposure among non-smoking adults fell by almost 30 per cent after smoke free legislation was introduced in England in 2007, researchers in the Department for Health have found.
...Professor Anna Gilmore, who directed the study, said: “The importance of this study is that it examines the impacts of smoke free policies on adults’ exposure using a specific biological-marker of smoke exposure (rather than self-reported exposure) while simultaneously controlling for underlying declines in exposure.
“To our knowledge it is the first study to do this. The fact it shows marked declines in adult exposure provides further evidence of the important public health benefits of smoke-free policies.”
What, if any, are these "public health benefits"? The study looked at cotinine readings in nonsmokers before and after the English smoking ban and found that they fell by 27%. Cotinine itself is perfectly harmless, but it is a bio-marker for nicotine which is, in turn, is a proxy for "secondhand smoke exposure". Nothing wrong with that, nor is there anything surprising about cotinine readings falling as a result of a total smoking ban in 'public' places.*
The graph below (which comes from the study) shows saliva cotinine levels in nonsmokers before and after the ban (click, as ever, to enlarge).
'SFL' indicates the start of the 'SmokeFree Legislation'. What is most striking about this graph is how much cotinine and, it must be assumed, secondhand smoke exposure declined before the smoking ban. After the ban, cotinine levels did not change for people living in smoking households and Gilmore found that people in social classes IV and V experienced no reduction in secondhand smoke exposure at all (inevitably, this leads to her calling for "further efforts to reduce SHS exposure to benefit those who remain most exposed.")
Only nonsmokers from social classes I to III who live in nonsmoking households saw a decline in their saliva cotinine levels. Gilmore claims that this decline was greater than would be expected from the long-term trend, although none of her graphs appear to support this.
Gilmore's track record gives us no particular reason to trust her assertion that the smoking ban accelerated the existing trend towards less secondhand smoke exposure. However, it is obviously very plausible that a smoking ban would have this effect so, for the sake of argument, let us agree that there was a 27% drop in saliva cotinine readings as a result of the ban.
Her data show that before the ban (1998 to 2007), average cotinine levels in nonsmokers' saliva fell from 0.36 ng/ml to 0.14 ng/ml. After the ban, this declined continued and, by the end of 2008, cotinine levels were at 0.071 ng/ml.
The question is: so what? Is this decline—which sounds impressive when described as a 30% fall in secondhand smoke exposure—of any practical significance? How do these levels compare with actually smoking?
A systematic review of cotinine readings found that the average smoker has a saliva cotinine reading of 318 ng/ml. This is more than 2,250 times greater than levels found in nonsmokers before the ban.
This difference is so vast that it is difficult to show it visually. The graph below shows cotinine levels of nonsmokers in 1998, 2007 (pre-ban) and 2008 (post-ban) compared with a typical cotinine reading from a smoker. If you click to enlarge, you may just be able to see the nonsmokers' data.
While smokers have average cotinine readings of 318 ng/ml, the smoking ban reduced the average nonsmokers' levels by 0.0019 ng/ml. This is beyond negligible. Whether before or after the ban, we are talking about truly homeopathic levels of exposure. It takes a leap of faith to believe that reducing 'exposure' levels from 0.03% of a smoker's level to 0.02% of a smoker's level really constitutes "the most significant and beneficial public health intervention for a generation". Far from showing us how effective the smokefree legislation has been in tackling the passive smoking peril, this study reminds us how overhyped the peril was in the first place.
* However, it is wrong of the press release to describe a 27% fall in nonsmokers' cotinine levels as meaning that "second-hand smoke exposure among non-smoking adults fell by almost 30 per cent". This suggests that if all secondhand smoke was eliminated, cotinine levels would fall to zero. This would never happen because nicotine, and therefore cotinine, exists at low levels in various nightshade vegetables.
