Tuesday, June 27, 2006

Surgeon General Does Not Conclude that 30 Minutes of Secondhand Smoke Causes Atherosclerosis; Time for Anti-Smoking Groups to Retract their Claims

Despite containing more than 727 pages of extensive review of nearly every possible health manifestation of exposure to secondhand smoke, the Surgeon General's report released today does not conclude that there is any severe or fatal cardiovascular impact of a single acute (i.e. 30 minute) exposure to secondhand smoke, as currently claimed by more than 80 anti-smoking groups.

The report does review the scientific literature regarding the acute cardiovascular effects of secondhand smoke. It reviews studies of the effects of brief secondhand smoke exposures (from 5 minutes to 2 hours) on artery elasticity, endothelial function, platelet activation, lipid metabolism, and heart rate variability. It finds that these brief exposures cause changes in platelet and vascular function that may be as large as those observed in active smokers.

However, it appropriately uses these data to conclude that this scientific literature provides biologic plausibility of a relationship between chronic secondhand smoke exposure and heart disease and to provide a plausible reason why the observed relationship between the dose of tobacco smoke (active vs. passive smoking) and the clinical effect (heart disease) is not linear.

Unlike what a large number of anti-smoking groups are doing, the Surgeon General's report does not use these data to suggest to the public that a short exposure to secondhand smoke can therefore cause atherosclerosis, clogged arteries, blood clots in arteries, narrowed arteries, cardiac arrhythmias, heart attacks, and death.

Instead, the report concludes that: "findings of a wide variety of clinical and experimental studies of various designs demonstrate that the effects of secondhand smoke on the cardiovascular system occur at low doses in nonsmokers, with some of the effects (on platelets and vascular function) similar to those in active smokers. For this reason, it is not appropriate to scale from the effects of active smoking in a linear, dose-dependent approach to estimate the effects of exposure to secondhand smoke based on comparative doses of smoke components (Howard and Thun 1999). Secondhand smoke interferes with the normal functioning of the heart, blood, and vascular systems in ways that increase the risk of a cardiac event. For some of these effects (changes in platelet and vascular function), the immediate effects of even short exposures to secondhand smoke appear to be as large as those seen in association with active smoking of one pack of cigarettes a day. Some evidence indicates lower levels of circulating antioxidants associated with secondhand smoke exposure. The experimental and observational evidence reviewed in this chapter supports the plausibility of the findings of the epidemiologic studies reviewed in Chapter 8 (Cardiovascular Diseases from Exposure to Secondhand Smoke). The large body of evidence documenting that secondhand smoke produces substantial and rapid effects on the cardiovascular system demonstrates that even a brief exposure to secondhand smoke has adverse consequences for the heart, blood, and blood vessels...".

It is important to note that the adverse consequences being referred to here on the heart, blood, and blood vessels include decreased artery elasticity, endothelial dysfunction, platelet activation, impaired lipid metabolism, and decrease in heart rate variability. They do not refer to hardening of the arteries, blood clots, clogged arteries, impaired coronary artery blood flow, heart attacks, catastrophic arrhythmias, or death.

Interestingly, while a large number of anti-smoking groups are claiming that acute exposure to secondhand smoke causes atherosclerosis, the report does not even conclude that chronic exposure to secondhand smoke causes hardening of the arteries (atherosclerosis). Instead, the report concludes that there is suggestive evidence, but that it is premature to draw definitive conclusions: "Studies of secondhand smoke and subclinical vascular disease, particularly carotid arterial wall thickening, are suggestive but not sufficient to infer a causal relationship between exposure to secondhand smoke and atherosclerosis."

The Rest of the Story

I think it is now time for the 80+ anti-smoking groups that have made or are making the fallacious scientific claim that 30 minutes of exposure to secondhand smoke represents a severe and potentially fatal cardiovascular risk for the population of nonsmokers retract or correct their claims.

If a 727-page, comprehensive report that provides an in-depth and exhaustive review of the health effects of secondhand smoke fails to conclude that there is any risk of atherosclerosis, heart disease, heart attacks, or heart disease-related death from a brief exposure to secondhand smoke, then I think these groups do not have a leg to stand on in continuing to disseminate their fallacious claims.

And if the report does not even conclude that chronic exposure to secondhand smoke causes hardening of the arteries, it is hard to justify telling the public that just 30 minutes of exposure to secondhand smoke causes hardening of the arteries.

It has become clear that these claims are not supported by the evidence, and given the high visibility of the Surgeon General's report, the anti-smoking groups are now certainly aware of this. Thus, any prolonged delay in retracting or correcting these claims can only be interpreted as suggesting that the anti-smoking groups have no sincere interest in reporting and communicating the truth.

The Rest of the Story will be following the status of these fallacious claims over the next week, and reporting on any retractions or changes that are made. Given the failure of the Surgeon General's report to provide any support for the claims being made by anti-smoking groups, I think it is not unreasonable to expect that most, if not all, of these fallacious claims should and will be retracted over the course of the next week.

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