Impact of E-cigarettes on Respiratory Symptoms: A Literature Review

This literature review investigates the impact of e-cigarettes on respiratory symptoms. The study found that e-cigarettes can lead to adverse effects on the airways, but can also be used as a means to quit or cut down smoking. The review suggests the need for more research in this area.

Introduction
Electronic cigarettes, commonly called as e-cigarettes, are the electronic gadget that generate a
smoke‐like spray known as vapour. The consumer inhales the vapour. This vapour produced by
the e-cigarettes characteristically has nicotine content but majority of the other chemicals that
people are exposed to with conventional cigarette smoking. E-cigarettes are popularized among
the people who smoke nut want to cut down on the hazards of smoking. It is reported through
several studies that e-cigarettes use may enhance the vulnerability to respiratory infections. But
the data on the issue of respiratory health of e-cigarettes users is limited. The given study is done
to investigate the alterations in respiratory manifestations in individuals who smoke traditional
cigarette and swapped to vaping for minimum of two month period. An on-line survey was
conducted to examine the subjective changes. The research found that 29% participants claimed
no alterations in respiratory manifestations, 5% claimed deterioration, and 66% claimed
improved condition. So, the study concluded that the shift from smoking to vaping is related to a
decreased occurrence of self-reported respiratory symptoms and identified the need of more
research which can use objective measures in randomly selected samples. However, this study
has several limitations. The reporting was subjective and it could be possible that the e-
cigarette’s users attempted portraying vaping in a positive light to reduce the anti-vaping ideation
of public health and media reporting of vaping. Another limitation is that vapers who faced
negative impacts while vaping may have left using e-cigarettes and were not part of the sample.
Findings of this study were in contrast with the findings of cell culture and animal studies, but
those studies also had various limitations. Moreover, human studies have not found any negative
impacts of vaping.
One of the major preventable causes of death and disability, and social disparity in health in the
UK is smoking (Tobacco Advisory Group of the Royal College of Physicians , 2016). If nicotine
is provided to the addicted smokers devoid of the damaging elements of tobacco smoke, majority
of the damage from smoking can be prevented. E-cigarettes provide nicotine without the burning
of chemicals and for this reason, regarded as a safer option than traditional cigarettes. However,
some cell and animal researches have indicated the possibility of risks proposing that vaping may
enhance the vulnerability to respiratory infections. Cigarette-smokers who have attempted to quit

using other methods and failed can be motivated to try e-cigarettes to quit smoking and the stop
smoking services need to assist e-cigarette smokers in quitting by providing behavioral support
to them. There is a lack of evidence regarding the usefulness of e-cigarettes in undermining the
long-term reduction in cigarette smoking among young adults, and may actually be playing a
part in promoting it. An overall shift has been observed towards the incorrect perception of e-
cigarettes having as adverse effects as the conventional cigarettes in the past year as opposed to
the current estimation that using e-cigarette is approximately 95% safer than traditional cigarette
smoking (Preston, 2015). Further investigation is required in this area. This literature review is
conducted to find evidence in favour and against the use of e-cigarettes in causing respiratory
symptoms.
Method
Literature was reviewed systematically. Relevant articles were found through the databases of
MEDLINE, ScienceDirect, PubMed, CINAHIL and many more. The studies published in last 10
years and in English language were selected. Studies which examined the link between e-
cigarette use and respiratory infections were considered. Several long and short terms were
included to search for the topic. Keywords used for primary search were “e-cigarettes” and
“vaping” “respiratory symptoms”, “respiratory infections”, “vapers”, “nicotine”. Boolean
operators (AND, OR) were used to make the search more focused and productive. Another
search was undertaken using medical subheading (MeSH). In addition, Google Scholar was used
for search. Lastly, all the retrieved articles were checked for their reference list manually and any
relevant article were included. Abstracts of the selected articles were screened to determine if
they were specifically relevant for the research topic. After that, the articles were analyzed for
presentation of data regarding the association between vaping and any measure of respiratory
symptoms. 46 studies were found, out of which 12, articles are eventually included in the
literature review. Two major themes were identified, Adverse effects on the airways and E-
cigarette used an aid to quit or cut down smoking. One denoted the positive aspect effect of
vaping while other indicated towards the negative aspect.
Inclusion criteria
1. Pertaining to the research topic

2. Published within 2009-2019
3. English language
Exclusion criteria
1. Older studies
2. Non-English
Discussion
Adverse effects on the airways
It can be said that e-cigarettes have gained huge increases in popularity in last five years because
of excessive marketing, enhanced constraints on the usage of on traditional cigarettes, and a due
to the perception that e-cigarettes are safer substitutes to conventional cigarettes. Current studies
have established that e-cigarettes can aid smokers in quitting smoking and lower their cigarette
use. Evidence is also found that e-cigarettes can inspire quitting or cigarette use decline even
among the people who don’t intend to quit or reject the support. The consumption of e-cigarettes
is increasing rapidly particularly among youth as e-cigarettes are perceived as a safer option as
compared to the traditional cigarettes. But, the evidence considering the impact of e-cigarettes on
the lung is very scarce. A study was conducted is to ascertain if use of e-cigarette changes the
subject airway epithelial functions against respiratory viral infection. The study revealed that
nicotine-free e-liquid promoted IL-6 generation and HRV infection. Including nicotine into e-
liquid enhanced the impact of nicotine-free e-liquid. Result of this study provided a strong
evidence for the adverse effects on the airways of young individuals by the e-cigarettes
particularly the airway epithelial inflammation and innate immunity. Moreover, this study can
guide future research to assess the effect of e-cigarettes on lungs of human, particularly the youth
so that public can be informed regarding the potential health risks of e-cigarettes (Wu, et al.,
2014). However, this study has several limitations. Several e-cigarette components such as
propylene glycol have received approval from the FDA to be consumed by humans as liquid,
however their safety in the form of vapor for inhalation is not researched. A recent study
revealed well-distinguished young hTBE cells at the air-liquid interface culture to tobacco-
flavored e-cigarette vapour with the use of a cell exposure chamber as indicated in past tobacco
cigarette smoke study (Wu, et al., 2012) (Zhang, et al., 2011). Second limitation is that this study

emphasised on the acute exposure impact of e-liquid on airway epithelial functions. Therefore,
study with chronic to e-liquid or e-cigarette vapor with or without HRV
infection in vitro and in vivo needs to be undertaken to assess the chronic impact of e-cigarette
consumption on airway epithelial functions. Lastly, the study did not investigate the molecular
mechanism underlying IL-6 up-regulation by e-liquid treatment.
Literature suggested that the research on the issue of deleterious impact of e-cigarettes is at the
initial stages. A range of recent researches made a comparison between the cytotoxic impact of
e-cigarettes and traditional tobacco cigarettes. Those studies found that exposing to e-cigarette
vapor with nicotine causes much less cytotoxic impact as compared to traditional tobacco
cigarette smoke (Farsalinos, et al., 2013) (Cervellati, et al., 2014).
The findings of this study was supported by another study that was done to ascertain if exposure
to e-cigarette has effect on respiratory immune defenses against microorganisms that are usually
linked with acute exacerbations of COPD. Substantial damage in bacterial clearance in lungs of
mice which had exposure to e-cigarette for 14 days was observed. Weak poor bactericidal
activity was also observed partially because of the malfunctioning bacterial phagocytic activity
by alveolar macrophages harvested from mice exposed to e-cigarettes as compared to air
controls. It was shown previously that mice that were exposed to cigarette smoke for 7 days
demonstrated defective bacterial phagocytosis (Harvey, et al., 2011), which is in line with the
impact of this study after exposure to e-cigarette vapor. It has been demonstrated previously that
cigarette smoke changes surface expression of scavenger receptors which play a significant role
in bacterial detection and uptake, but exposure to e-cigarette did not change surface expression
of macrophage scavenger receptors, MARCO or CD36. So the study concluded that exposure to
e-cigarettes leads to immunomodulatory impact which are similar to those found after exposure
to conventional cigarette smoke. Advancement of COPD disorder can be majorly driven by the
bacterial and viral exacerbations, so this study alarms that people with COPD who shift from
cigarette smoking to e-cigarette smoking may not get considerable improvement in their disease
course. The study has several limitations. The exposure was planned to model the nicotine
strengths of e-cigarette consumers but, reports of serum nicotine strengths are hugely variable,
and many accounts show that nicotine strength in e-cigarettes is usually less than in traditional
cigarettes. The choice of menthol e-cigarettes in this study may not accurately represent other

flavors. E-liquids which are menthol are moderately cytotoxic compared to other flavours (Bahl,
et al., 2012), and there is little evidence to demonstrate that menthol-flavoured cigarettes are
more or less toxic than other cigarettes. But, menthol controls nicotine metabolism, and
therefore, may have health effects which are not seen with other flavours. This limitation of the
study was partially addressed by giving exposure to the group of mice to conventional e-cigarette
vapour, and similar effect was seen on inflammatory cell number and ex vivo bacterial clearance
as opposed to menthol e-cigarette vapour (Sussan, et al., 2015).
E-cigarette used a meansto quit or cut down smoking
It is remarkable that e-cigarettes gained popularity because they were perceived as safer
alternative or were used to quit smoking. A review was done to reveal if e-cigarettes assist the
smokers in quitting or cutting down smoking, and whether it was safe to consume e-cigarettes to
do this. Trials published in and before July 2014 were searched for this review and 13 trials were
found relevant. The review found that consuming an e-cigarette with nicotine amplified the risk
of quitting smoking long‐term as opposed to consuming an e-cigarette devoid of nicotine.
Consuming an e-cigarette with nicotine also assisted more smokers decrease the quantity they
smoke by minimum 50% as compared to consuming an e-cigarette devoid of nicotine. However,
the study was not able to find out if e-cigarette was an improved choice than a nicotine patch to
people in quitting smoking as the sample size of the study was low. The review also
demonstrated that people who consumed e-cigarette had increased chances of reducing the
cigarette quantity they smoked by minimum 50% of the people using a patch. Various other
studies supported this finding but their quality of evidence was lower. No evidence was found to
show that consuming e-cigarette along with using conventional cigarettes rendered people less
prone to stop smoking. No study found that smokers who consumed e-cigarette for 2 years or
less had an enhanced health risk than to the smokers who did not consume e-cigarette. But this
review has limitation. The total evidence quality is low as very number of studies were used to in
the review to derive inference (McRobbie, et al., 2014).
Another study was conducted to report for the impact of e-cigarettes on subjective and objective
asthma criteria for the first time and the tolerability in smokers who have asthma and who
stopped or cut down their tobacco intake by adopting these products. The study reviewed the
changes retrospectively in spirometry data, airway hyper-responsiveness (AHR), exacerbations

of asthma and subjective asthma regulation in people with asthma who adopted regular e-
cigarette use. In the study, 18 people with asthma who smoked were identified. The study
revealed significant overall improvements in spirometry data, asthma regulation and AHR.
Single as well as dual users both demonstrated these positive outcomes. Insignificant decline in
exacerbation rates was noted. There was no report of any severe adverse events. The study
indicated that frequent usage of e-cigarettes as an alternative to smoking is related to objective
and subjective improvements in asthma consequences. So, the study concluded that since e-
cigarette have shown less harm than conventional cigarettes and can result in decreased cigarette
intake with consequent improvements in asthma consequences, e-cigarettes are potential valid
substitute for patients of asthma who are unable to quit smoking by other techniques (Polosa, et
al., 2014).
The evidence of efficacy of e-cigarettes as an means to quit smoking is limited as compared to
the nicotine products which have approval as smoking quitting aids. The adults going to National
stop-smoking services in the UK to either nicotine-replacement products of their preference were
randomly assigned, including product combinations, given for up to 3 months, or an e-cigarette
starter pack, with a suggestion to buy further e-liquids of the flavour and concentration of their
preference. Treatment involved behavioral support once in a week for minimum 4 weeks. 886
participants went through randomization. e-cigarette group demonstrated the 1-year abstinence
rate of 18%, while the nicotine-replacement group showed 9.9% rate. Participants with 1-year
abstinence and were in the e-cigarette group were had increased chances of using their allocated
product at 52 weeks as compared to the nicotine-replacement group. In addition, e-cigarette
group more frequently reported in throat or mouth irritation and nausea as compared to the
nicotine-replacement group. The e-cigarette group also reported higher reduction in the episodes
of cough and phlegm formation from baseline to 52 weeks as compared to the nicotine-
replacement group. No substantial difference was found between the two group in occurrence of
wheezing or shortness of breath. Therefore, the concluded that e-cigarettes had higher chances of
being successful in quitting smoking than nicotine-replacement therapy, when both the groups
were complemented with behavioral assistance (Hajek, et al., 2019).
A study identified the features and consumption patterns of e-cigarette users by focusing the
buyers from one specific vape shop website in Netherlands. The participants were asked about

their smoking history, existing smoking and vaping status, motives for vaping, alleged danger,
and possible health alterations because of vaping. The study revealed that majority of the people
were smoking before they began vaping. Major number of participants had an agreement that as
opposed to the other smoking-quitting aids, they were able to quit smoking because of vaping.
Almost every customer were vaped regularly who used hi-tech open system equipment without
alterations and e-liquid with an average 10 mg/mL nicotine. Vapers also reported about using e-
cigarettes to quit smoking, as these are healthier option, and cost-effective. Majority of the
vaping population perceived vaping as ‘not that harmful’ to ‘not harmful’ at all, but 20% thought
that vaping is harmful. Over 50% stated that vaping is more pleasing than smoking. A significant
section of population reported improvement in their health since they began vaping. So, the
findings of the study were in line with other vape shop studies (Gucht, et al., 2017).
Conclusion
Consumption of e-cigarette use has grown tremendously in short period of time, particularly
among youth, in spite of scarcity of short-term and long-term safety data. A shift is observed in
the use of patterns of use which included never smokers and several dual consumers of e-
cigarettes and combustible tobacco cigarettes. A growing interest is seen in last few several years
on the issue of potential toxicities of e-cigarettes aerosols (Chun, et al., 2017). Substantial COPD
morbidity and mortality due to conventional cigarette smoking is established. But the efforts on
quitting smoking in people with COPD are weak and there is an alarming requirement to have
more effective approaches of quitting smoking in people with COPD. E-cigarettes are perceived
as safer option due to their reduced chances of developing respiratory infections and they may
also enable effective quitting efforts. It can be said that not much is known about the health
impact of e-cigarettes use among the people COPD who smoke and whether their frequent use
has any impact on subjective and objective COPD consequences (Morjaria, et al., 2017). After
reviewing the literature, the evidence supporting the scenario was moderate. In fact, several
studies concluded against the scenario. Certain studies identified the adverse consequences of e-
cigarette smoking on the youth and mice populations. Studies also affirmed that e-cigarette may
help in quitting or reducing their smoking frequency. One study indicated that regular use of e-
cigarette as alternative smoking is linked with objective and subjective improvements in asthma
outcomes. However, all the studies had various limitations, therefore, more research is required

with strong and validated studies are required. More research is required to scrutinise the
contribution of various e-cigarette extracts, flavors, nicotine concentrations, propylene
glycol/glycerin mixtures, vapor delivery devices, on respiratory system. Studies must focus on
long exposure. Studies are also required to investigate the mechanism by which exposure to e-
cigarette affects microbial infection. E-cigarettes are becoming immensely popular especially
among youth population, which can cause a budding threat to public health in context of
recurring microbial infections. So, it can be concluded that in spite of the common perception
regarding the safety of e-cigarettes, literature provides evidence of its negative effects to
respiratory health as well therefore, e-cigarettes need to be investigated more thoroughly,
particularly in vulnerable groups.
References
Bahl, et al., 2012. Comparison of electronic cigarette refill fluid cytotoxicity using embryonic
and adult models. Reprod Toxicol, Volume 34, p. 529–537.
Cervellati, et al., 2014. Comparative effects between electronic and cigarette smoke in human
keratinocytes and epithelial lung cells. Toxicol In Vitro, Volume 28, p. 999=1005.
Chun, L. F. et al., 2017. Pulmonary toxicity of e-cigarettes. Am J Physiol Lung Cell Mol
Physiol., 313(2), pp. 193-206.
Farsalinos, et al., 2013. Comparison of the cytotoxic potential of cigarette smoke and electronic
cigarette vapour extract on cultured myocardial cells. Int J Environ Res Public Health, Volume
10, pp. 5146-5162.
Gucht, D. V., Adriaens, K. & Baeyens, F., 2017. Online Vape Shop Customers Who Use E-
Cigarettes Report Abstinence from Smoking and Improved Quality of Life, But a Substantial
Minority Still Have Vaping-Related Health Concerns. Int J Environ Res Public Health, 14(7).
Hajek, P. et al., 2019. A Randomized Trial of E-Cigarettes. The New England Journal of
Medicine .
Harvey, et al., 2011. Targeting Nrf2 signaling improves bacterial clearance by alveolar
macrophages in patients with COPD and in a mouse model. Sci Transl Med, Volume 3.

McRobbie, H., Bullen, C., Hartmann‐Boyce, J. & Hajek, P., 2014. Electronic cigarettes for
smoking cessation and reduction. Cochrane Systematic Review.
Morjaria, J., Mondati, E. & Polosa, R., 2017. E-cigarettes in patients with COPD: current
perspectives. Int J Chron Obstruct Pulmon Dis, Volume 12, pp. 3203-3210.
Polosa, R. et al., 2014. Effect of Smoking Abstinence and Reduction in Asthmatic Smokers
Switching to Electronic Cigarettes: Evidence for Harm Reversal. Int. J. Environ. Res. Public
Health, 11(5), pp. 4965-4977.
Preston, W., 2015. E-cigarettes: An evidence update. A report commissioned by Public Health
England., London: PHE.
Sussan, et al., 2015. Exposure to Electronic Cigarettes Impairs Pulmonary Anti-Bacterial and
Anti-Viral Defenses in a Mouse Model. PLoS ONE, 10(2).
Tobacco Advisory Group of the Royal College of Physicians , 2016. Nicotine without smoke-
tobacco harm reduction, s.l.: Royal College of Physicians.
Wu, Jiang & Chu, 2012. Cigarette smoke induces growth differentiation factor 15 production in
human lung epithelial cells: implication in mucin over-expression. Innate Immun, Volume 18, p.
617–626.
Wu, Jiang, Minor & Chu, 2014. Electronic Cigarette Liquid Increases Inflammation and Virus
Infection in Primary Human Airway Epithelial Cells. PLoS ONE , 9(9).
Zhang, et al., 2011. igarette smoke modulates PGE(2) and host defence against Moraxella
catarrhalis infection in human airway epithelial cells. Respirology , Volume 16, pp. 508-526.