Table 2.

Characteristics of systematic reviews on respiratory/pulmonary health risks of e-cigarettes.

Author, Year	Funding/COI Disclosures of Review Authors	Objectives	Date Range of Literature Search	Evidence Type	Health Outcome Measures		Study Designs	Population	Number of Included Studies	Exposure	Vaping Devices
					Acute	Chronic
Glasser et al., 2017 [28]	N/A	Synthesize empirical studies on electronic nicotine delivery systems across a broad range of topics, including the health effects.	Through 31 May 2016	Human	Lung function, changes in COPD/asthma disease symptoms (time of assessment unspecified).		Experimental, quasi-experimental, observational (including case control, cohort and cross-sectional), case reports, case series, qualitative studies, mixed methods.	N/A	116 articles on the impact of vaping on human health.	Exposure to vapor (duration not specified).	N/A
Gualano et al., 2014 [17]	N/A	A systematic review of published studies in order to investigate the efficacy and the adverse effects of the EC.	Through April 2014	Human	Respiratory resistance	N/A	Experimental	N/A	One study	Short-term use of EC (duration not specified).	N/A
Pisinger & Dossing, 2014 [21]	Authors report no conflict of interest.	(1) Systematic and critical review of the existing literature on the health consequences of ECs and discuss the implications of our findings for public health; and (2) to investigate how many of the published articles have a conflict of interest.	Through 24 August 2014	Human, Animal	Acute changes in airway resistance, obstruction, and spirometry-assessed lung function.	N/A	Experimental	Human studies: Generally healthy participants. The results show that three studies included participants with asthma/COPD. Animal: mice.	Six human and one animal studies on pulmonary health effects.	Short-term EC use (minutes) * Intra-tracheal application of a diluted e-liquid solution 2× week for 2 weeks.	N/A
Bozier et al., 2020 [18]	None declared	(1) To provide a comprehensive update of data on the potential health effects of ECs since the NASEM report. (2) To provide a focused discussion of the scientific literature that will help inform the general public, health-care practitioners, and policy makers of the effects of EC use on health.	February 2017 through May 2019	Human, Animal	Changes in lung function in animals and humans. Changes in respiratory symptoms in COPD/asthma patients.		Experimental, observational, and case reports.	Not specified.	14 studies on respiratory/pulmonary health effects.	Short-term and long-term EC use or exposure to EC vapor (no data on the duration).	N/A
Harrell et al., 2014 [19]	The authors report no conflicts of interests. One co-author reports to be receiving research support from a pharmaceutical company, which is also a manufacturer of a stop smoking medication.	To have a summary of the current, relevant literature on EC safety and efficacy.	Through November 2013	Human	Acute changes in respiratory resistance, lung function (no definition of “acute”).	N/A	Case series and case reports.	Not specified. The results show that some studies included smokers and never smokers. No information on their health.	Eight studies on acute physiological effects.	EC use (no data on the duration).	EC devices reported partially in a Table with study characteristic. No summary or discussion provided.
NASEM, 2018 [16]	N/A	To evaluate the available evidence of the health effects related to the use of electronic nicotine delivery systems (ENDS) and identify future federally funded research needs.	1 February 2017–31 August 2017	Human	Intermediate outcomes (measurements of lung function and lung structure, quantification of inflammatory cell numbers from bronchoalveolar lavage (BAL), pro-inflammatory cytokines from bronchial biopsies, and improvement and progression of existing respiratory diseases.	Development of respiratory conditions, such as asthma, pneumonia, and COPD.	Experimental, observational.	Subjects with or without preexisting respiratory disease.	17 human studies.	Acute (minutes to hours) and long-term (not further defined) vaping.
Ioakeimidis et al., 2016 [20]	N/A	To highlight the efficacy for smoking cessation and the potential hazards of EC use.	Through June 2015	Human	Acute effects on pulmonary function (No definition of “acute”).	N/A	Not specified. Original studies as well as review articles and statements.	N/A	20 original studies and 8 review articles and statements	EC use (no data on the duration)	N/A
Bravo-Gutierrez et al., 2021 [27]	Authors declared no conflicts of interest.	To describe the adverse effects on the respiratory system in consumers of ECs.	January 2013–August 2020	Human, animal, in vitro	Acute and sub-acute effects on DNA damage, inflammation mechanisms, and reactive oxygen species (ROS) presence.	Chronic effects on DNA damage, inflammation mechanisms, ROS presence.	Experimental, laboratory.	N/A	N/A	Acute (2 h daily for 3 days), sub-acute (2 h daily, 5 days a week for 30 days), and chronic (no definition) inhalation	N/A
Chand & Hosseinzadeh, 2021 § [31]	Authors declared no conflicts of interest.	To evaluate the most recent studies exploring the association between EC use and asthma worldwide.	2007–March 2021	Human	Self-reported asthma diagnosis.		Observational	Youth and adult current EC users, ever EC users and dual EC and TC users.	13 cross-sectional studies.	Current EC use (past 30 days), ever EC use (ever use but not in past 30 days), dual use (use of EC and TC in past 30 days).	N/A
Larue et al., 2021 § [29]	No competing interests for this work were declared. The review protocol declares that a family member of the lead author works in tobacco industry.	To assess the immediate respiratory effects of acute EC use.	Through 20 May 2021	Human	Augmentation index, fraction of exhaled nitric oxide (FeNO), and spirometry measures.	N/A	Experimental	Mostly healthy participants. Current smokers and non-smokers.	17 cross over and randomized trial studies.	Duration of EC use (with and without nicotine) ranged from 3 to 30 min. Assessment time occurred between 1 and 30 min post use.	Different brands of ECs with varying nicotine content.
Xian & Chen, 2021 § [25]	Authors declared no conflicts of interest.	To explore the relationship between ECs and the risk of asthma.	Through August 2020	Human	Asthma diagnosis		Observational	Adolescents and adults with diagnosed asthma, who are current or former EC users or smokers (comparators).	11 cross-sectional studies.	Current and former EC use (no further definition).	N/A
Goniewicz et al., 2020 [24]	First author received research grant from Pfizer and personal fees from Johnson & Johnson outside of this work. Other authors have nothing to declare.	To conduct a systematic review of epidemiological studies that estimated the odds of key respiratory outcomes among EC users who formerly smoked, compared with current smokers who do not use ECs.	Through September 2020	Human	Respiratory outcomes (COPD, chronic bronchitis, emphysema, asthma, and wheezing).		Observational	Adult former smokers who transitioned to EC use and current exclusive TC smokers (as a comparator).	Two cross-sectional and one prospective.	EC use (no data on the duration).	N/A
Wills et al., 2021 § [23]	Authors declared no conflicts of interest.	To provide a comprehensive review and meta-analysis of evidence from epidemiological studies about the association of EC use with asthma and COPD in human populations.	Through March 2020	Human	Asthma and COPD.		Observational	General population of adolescents and adults.	15 studies on asthma and nine for COPD (seven cross-sectional and two prospective).	EC use (current use, 30-day use, and long-term use).	N/A

§ Meta-analysis. COI = conflict of interest; EC = electronic cigarettes; TC = traditional cigarettes; COPD = chronic obstructive pulmonary disease; ROS = reactive oxygen species; FeNo = fraction of exhaled nitric oxide; and N/A = not available. * Duration of exposure varied according to the followed intervention protocols.