A new study published in the American Journal of Preventive Medicine purports to show that the use of e-cigarettes causes long-term lung damage. The study found that adults who used e-cigarettes at baseline and had never been diagnosed with lung disease were more likely than non-vapers at baseline to be told that they have lung disease after three years of follow-up. The study controlled for whether or not a person reported smoking at baseline, but not for their lifetime history of cigarette consumption.
Based on these findings, the authors concluded that: "Use of e-cigarettes is an independent risk factor for respiratory disease in addition to combustible tobacco smoking. Dual use, the most common use pattern, is riskier than using either product alone."
National and international media headlines reported that e-cigarettes have now been recognized as causing long-term lung damage, including chronic lung disease (COPD).
The Rest of the Story
This study is deeply flawed because it fails to consider the most likely explanation for the study findings: that people who use e-cigarettes more likely have a history of more intense smoking than people who do not use e-cigarettes. For example, one study found that while only 21% of adult smokers who did not vape were heavy smokers, 68% of adult smokers who did vape were heavy smokers (or had been heavy smokers).
This is critical because it shows that in order to control for smoking history properly in a study such as this one, you cannot merely control for whether or not someone was a current or ever smoker at baseline. You have to actually control for the person's overall smoking history including whether they were a heavy smoker and how many years they smoked.
Importantly, this study did not control for a person's smoking history.
Because smoking history is such a strong predictor of the development of chronic lung disease, the failure to control for smoking history invalidates the results of this study. In my view, it does not provide any evidence that e-cigarette use causes lung disease. What it does show, in contrast, is that smoking is a strong predictor of lung disease and that heavier intensity of smoking increases the risk.
It is not even plausible that e-cigarette use could cause COPD within three years. Even with heavy smoking, it takes decades before a person develops COPD. If you walk into a respiratory intensive care unit, you're not going to find a lot of COPD patients in their 30s or even 40s. So if it takes at least three decades of smoking to develop COPD, how is a person supposed to develop COPD from e-cigarettes in only three years?
The most telling aspect of the study is that it failed to report the risk of COPD associated with the use of e-cigarettes among people who never smoked. If e-cigarettes can cause lung disease within just three years, then one would expect to see many never smokers who started vaping to develop COPD within three years. This is simply not happening and this study doesn't even bother to test for it.
Moreover, the study fails to examine the risk of COPD development among smokers who exclusively used e-cigarettes at baseline and those who continued to smoke. Such an analysis would show that switching to e-cigarettes actually reduces the risk of COPD among smokers. But if you don't test for such a relationship, you can't possibly find it. That's why you won't find these authors conducting any such analysis any time soon.
Fortunately, numerous other studies have examined the risk of lung function and respiratory symptoms among smokers who switch to e-cigarettes compared to smokers who continue to smoke. These studies have reported dramatic improvements in lung function--both objectively and subjectively--among smokers who quit by switching completely to e-cigarettes.
This evidence demonstrates that the truth is the opposite of what is being reported here. E-cigarette use is not a cause of chronic lung disease. On the contrary, it helps improve respiratory health among smokers who are able to quit completely using these products.