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expert reaction to study looking at second hand nicotine vaping in the home and respiratory symptoms in young adults

A  study published in Thorax looks at second hand nicotine vaping at home and respiratory symptoms in young adults.


Prof Lion Shahab, Professor of Health Psychology and Co-Director of the UCL Tobacco and Alcohol Research Group, University College London (UCL), said:

“This paper reports on the potential impact of secondhand nicotine vape exposure in young adults on respiratory symptoms. After controlling for various potential confounders such as young adult’s own use of cigarettes, e-cigarettes or cannabis as well as secondhand exposure to cigarette or cannabis smoke, young adults who were exposed to secondhand nicotine vaping were more likely to report respiratory symptoms than those who were not. While this finding is worrying and deserves further investigation, the results should be seen in context of the limitations of this study.

“First, as a purely observational study, these findings cannot establish a causal association. There may be other important confounders that may have contributed to these results. For instance, the measure of exposure was limited to the household of young adults and did not include exposure that may occur outside the household (e.g., during socialising with friends), neither did the study control for the type of housing or measure socioeconomic position. Because young adults were not randomly selected and essentially self-selected into different exposure groups, these factors may have contributed to differential respiratory symptoms (so called unmeasured confounding). Further, own use of products was not assessed as a lifetime measure but restricted to use in the last 30 days. Respiratory symptoms can persist even after stopping product use for a month, and it would have been preferable to assess own use of products over a longer time horizon. This study also did not verify product use objectively (e.g., measuring metabolites of exposure to nicotine in young adults), which is problematic as self-reported product use in this population may be biased due to social pressure not to admit to use of, e.g., cigarettes. In addition, as acknowledged by the authors, the vast majority of participants with secondhand nicotine vape exposure (up to 93.1%) also reported either past 30-day personal use of tobacco or cannabis products or exposure to combustible products. This high level of collinearity (i.e., co-occurrence of the main variable of interest, secondhand vape exposure, with relevant confounders) can make it difficult to disentangle reliably the individual contribution of secondhand vape exposure from those of other potential causes of respiratory symptoms in statistical analyses. While the authors undertook a number of sensitivity analyses, they did not look separately at the subgroup of participants who experienced only secondhand vape exposure and none of the other types of exposure (either personal or secondhand exposure of tobacco or cannabis products). Such stratified analysis would provide the strongest evidence of a true association. Lastly, numerous air quality studies have shown that particle exposure in households with secondhand smoking is much greater than in households with secondhand vaping, so it is surprising that the observed effect on respiratory symptoms seen in this study was similar in size to that observed for secondhand smoking (suggesting that unmeasured or imperfectly controlled confounding may have contributed to the result).

“This is not to say that there is no effect of secondhand nicotine vape exposure on respiratory symptoms in young adults. However, these findings will need to be replicated using objective measures of exposure, controlling for a more comprehensive list of potential confounders and including a sufficiently large sample of participants who have no exposure to products other than e-cigarettes. It will be important to establish whether these results hold in more stringent analyses as this would have clear implications for policy decisions on restricting exposure to secondhand vaping.”


Prof Peter Hajek, Director of the Tobacco Dependence Research Unit, Queen Mary University of London (QMUL), said:

“The article reports an association between questionnaire answers that respondents experienced cough/phlegm/shortness of breath and that they are living in households where people vape.  One of the problems in considering the association to be causal is that almost all participants smoked or vaped themselves and/or lived with people who also smoke (208 out of 223).  Surprisingly, no data on the association between the respiratory questionnaire and smoking are presented.  Another problem is that a credible explanation of a mechanism is needed if the reported association is to be considered causal.  While health risks of e-cigarettes to vapers themselves have been estimated at up to 5% of health risks of smoking, health risks to bystanders are most likely reduced by a much bigger margin, and most likely altogether.  This is because e-cigarettes release no chemicals into the environment themselves, only what users exhale, and such exhalation has so far not been shown to generate any toxicants at levels that could conceivably affect the health of bystanders.”



‘Secondhand nicotine vaping at home and respiratory symptoms in young adults’ by Talat Islam et al. was published in Thorax at 23:30 UK time on Monday 10 January 2022.

DOI: 10.1136/thoraxjnl-2021-217041



Declared interests

Prof Peter Hajek: “No conflict of interest.”

Prof Lion Shahab: “None.”

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