Krisha Reddy and colleagues just published “ Respiratory Symptom Incidence Among People Using Electronic Cigarettes, Combustible Tobacco, or Both” in American Journal of Respiratory and Critical Care Medicine that showed that dual use of e-cigarettes and cigarettes doubled the odds of developing respiratory symptoms (aOR 2.22, 95% CI 1.79-2.75). This was a statistically significantly bigger increase in risk than the effects of smoking alone (1OR 1.24, 95% CI 1.00-1.55).
This finding is consistent with the existing literature on respiratory effects of e-cigarettes. It is also particularly important because they found that dual use was twice as prevalent as people solely using e-cigarettes (2.7% vs 1.4%). In other words, most people who are using e-cigarettes are not “switching completely” from cigarettes, but simply adding e-cigarettes to their cigarette smoking.
While the study does not address why most people are dual users, it is likely that the youth in the sample started with e-cigarettes and then added cigarettes (the gateway effect) and the adults were smokers who tried e-cigarettes an unsuccessful smoking cessation device and ended up dual users.
Reddy and colleagues used the FDA/NIH PATH longitudinal dataset which followed people forward in time, the strongest kind of epidemiological study. They started with people without respiratory symptoms and saw who developed them the following year based on e-cigarette and cigarette use. The primary analysis included both youth and adults; a subsidiary analysis limited to adults found similar results.
Interestingly these risks are about the same that Dharma Bhatta and I estimated in our longitudinal study of the association between e-cigarette and lung disease, controlling for any current or former smoking of 1.29 (1.03-1.61). In that study we concluded that the effects of e-cigarette and cigarette use were independent; the similar results in the Bircan paper of nonsmokers only supports our earlier conclusions.
The point estimate for the effect of e-cigarettes alone on the odds of developing respiratory symptoms was elevated (aOR 1.17, 95% CI 0.79-1.74 for everyone and 1.19, 95% CI 0.62-2.26 for adults), but the effect was not statistically significant. The estimate for adults is, however, within the 95% confidence interval for the risk respiratory disease that that Dharma Bhatta and I found in in our longitudinal study of the association between e-cigarette and lung disease using PATH of 1.29 (95% CI 1.03-1.61).
The fact that dual use is more dangerous than smoking also is consistent with biological evidence that e-cigarettes have some different biological effects than cigarettes. Older thinking was that an e-cigarette was sort of a cigarette with less bad stuff (because there are no combustion products), but it is now clear that, while some of the toxins in e-cigarettes are similar to cigarettes — like the ultrafine particles — there are also toxins that have different effects. Thus, a dual user is exposing himself or herself to the toxins in the cigarette plus other toxins that are unique to e-cigarettes.
As the FDA and other regulatory bodies consider if e-cigarettes are “appropriate for the protection of public health” they need to keep in mind that the most common e-cigarette behavior is dual use, which increases risk compared to just smoking. These agencies also need to consider the unique toxic risks generated by e-cigarettes rather than simply assuming that they are not dangerous because there is no combustion. The added risks of dual use, combined with expanding youth nicotine addiction and deterring quitting smoking by diverting smokers away from approved FDA therapies for smoking cessation, suggest that e-cigarettes as they are actually used are harm enhancing.
The full citation is: Reddy KP, Schwamm E, Kalkhoran S, Noubary F, Walensky RP, Rigotti NA. Respiratory Symptom Incidence Among People Using Electronic Cigarettes, Combustible Tobacco, or Both. Am J Respir Crit Care Med. 2021 Apr 15. doi: 10.1164/rccm.202012-4441LE. Epub ahead of print. PMID: 33857396. It is available here.