A new study published online ahead of print in the journal Chest demonstrated that in contrast to both tobacco cigarette smoking and secondhand smoke exposure, which have been shown to cause acute impairment of lung function, electronic cigarettes have no acute effect on pulmonary function as measured by spirometry testing.
See: Constantine I. Vardavas, Nektarios Anagnostopoulos, Marios Kougias, Vassiliki Evangelopoulou, Gregory N. Connolly, Panagiotis K. Behrakis. Acute pulmonary effects of using an e-cigarette: impact on respiratory flow resistance, impedance and exhaled nitric oxide. Chest 2011.
Active smoking is known to impair lung function, as measured by pulmonary function testing of lung air flow rates (also called spirometry). For example, short-term active smoke exposure has been shown to reduce forced expiratory flow rates.
Secondhand smoke exposure has also been shown to impair lung function, as evidenced by decreased FEV1 and FEV1/FVC ratios in tobacco smoke-exposed nonsmokers.
In this study, 30 smokers used an electronic cigarette for for 5 minutes, with lung function tested before and after use. A control group of smokers used an electronic cigarette with the cartridge removed.
The study found "no differences between basic pulmonary measurements" between the two groups, demonstrating that acute exposure to electronic cigarette vapor did not affect FEV1, FVC, PEF or MEF50 and MEF75.
However, the study did find that acute electronic cigarette vapor exposure decreased exhaled nitric oxide and increased peripheral airway resistance.
The study concludes: "E-cigarettes assessed in the context of this study were found to have immediate adverse physiologic effects after short term use that are similar to some of the effects seen with tobacco smoking, however the long term health effects of e-cigarette use are unknown but potentially adverse and worthy of further investigation."
The Rest of the Story
It is first interesting to note that although the study's declared purpose was to "assess whether using an e-cigarette for five minutes has an impact on pulmonary function tests and exhaled nitric oxide," the study's abstract only reported the observed reduction in exhaled nitric oxide, not the lack of any effect on pulmonary function tests.
Moreover, the study failed to compare the acute respiratory effects of electronic cigarette exposure with those of active smoking, which is the most important comparison that needs to be made.
In contrast to what some are reporting, the study found no effect of e-cigarettes on lung function, as measured by spirometry. This is in contrast to tobacco smoking, which does have effects on lung function that can be measured using spirometric testing.
While previous research indicates that active smoking and even secondhand smoke exposure can affect acute lung function as measured by spirometry, the study demonstrated that electronic cigarette use led to no impairment of lung function detectable via spirometric testing.
What the study did show was subclinical evidence of impaired lung function, meaning that the observed (measurable) lung function was unchanged, but that there was evidence of physiologic effects consistent with some bronchial inflammation. What is not known is whether this acute bronchial inflammation has any significance in the long-term. The presence of bronchial inflammation may be a result of propylene glycol having a respiratory irritant effect. But this does not necessarily mean that long-term exposure would lead to any adverse effect on lung function. More research is necessary to clarify that point.
The authors acknowledge this: "We must state though that while the differences within our study are of statistical significance, the clinical changes may be too small to be of major clinical importance."
While this is only conjecture, I suspect that the study is detecting a respiratory irritant effect of propylene glycol. It will be interesting to see if the same effect is present or not with glycerin-based products.
The study does not change my overall assessment, which is that e-cigarettes are much safer than smoking. But it does suggest that e-cigarettes are not “safe” in any absolute sense (which we knew already because they contain nicotine). The real question is whether there are effects of long-term exposure to propylene glycol. Whether there are or not, I don’t think it will change the conclusion that e-cigarettes are much safer than smoking. However, it may have implications for the composition of e-cigarette liquid, as it may be that glycerin-based juice is safer than propylene glycol-based juice. It may be, for example, that a glycerin-based liquid fails to produce the airways inflammation that is being observed with a propylene-glycol based electronic cigarette.
In news coverage of the study, one of the authors was quoted as recommending: "If you're trying to quit, stick to the methods that are known to work." (i.e., nicotine replacement therapy and pharmacotherapy like Chantix and Buproprion).
I find this to be irresponsible advice, because these methods that are "known to work" actually are quite ineffective, with dismal results in terms of long-term cessation. Advising smokers to stick with the FDA-approved medications is tantamount to advising the overwhelming majority of smokers to continue smoking.
More importantly, since thousands of ex-smokers are remaining smoke-free with the help of electronic cigarettes, the study author's advice is essentially telling these ex-smokers that they are better off returning to active smoking than continuing to vape. Clearly, if these vapers switch to NRT or Chantix, they are very unlikely to be successful and will most likely return to cigarette smoking.
The American Council on Science and Health made the same point in its Facts and Fears column yesterday, writing: "The study’s lead researcher recommends that, instead of trying e-cigarettes as a reduced-risk method to quit smoking, smokers should “stick to the methods that are known to work.” But Dr. Ross criticizes this recommendation. 'He would have more accurately said, ‘stick to the methods that are known to not work,’ since those currently approved have a ‘success’ rate of only 5 to 10 percent. It’s the old ‘quit or die,’ abstinence-only agenda.'".
The rest of the story is that a propylene-based electronic cigarette system has been shown to produce airways inflammation in users, resulting in subclinical evidence of increased airway resistance. Whether long-term use of electronic cigarettes would lead to clinical manifestations due to actual airway obstruction is unclear, and more research is necessary to make such a determination. What we do know, however, is that long-term continuation of cigarette smoking will almost certainly lead to clinically significant airway obstruction.
The bottom line: if a smoker is choosing between active smoking and electronic cigarette use, the use of the electronic cigarette is clearly the wiser choice. And in fact, this is the choice that most electronic users are facing. The idea that any substantial proportion of electronic cigarette users will quit smoking if they take the article's advice and stick to approved NRT or pharmacotherapy products is unsupported by the scientific evidence.