INTRODUCTION: In this review, we aimed to explore whether nicotine e-cigarette or vaping product use impact respiratory health.

METHODS: We searched CINAHL, Embase, MEDLINE, PsycINFO, PubMed and Cochrane library databases initially in January 2023 and updated the search in January 2024. We included peer-reviewed human, animal, cell/ original studies published between July 2021 and December 2023 but excluded qualitative studies. Three types of e-cigarette exposure were examined: acute, short-to-medium term, and long-term.

RESULTS: We included 119 studies in the main analysis, and 5 in meta-analysis. Over half of the studies had low risk of bias. Non-smoker current vapers had higher incident risk of respiratory symptoms (relative risk, RR=1.90; 95% CI: 1.28-2.83) but statistically non-significant risk of chronic obstructive pulmonary disease (COPD) (RR=2.53; 95% CI: 0.96-6.67) compared to never users. They also had lower incident risk of respiratory symptoms compared to non-vaper current smokers (RR=0.75; 95% CI: 0.64-0.89) and dual users (dual use vs vaping, RR=1.26; 95% CI: 1.03-1.55). Dual users had higher risk of incidence of respiratory symptoms and prevalence of COPD compared to never users (RR=2.53; 95% CI: 1.44-4.45 and RR=3.86; 95% CI: 1.49-10.02, respectively), and the risk was statistically similar to non-vaper current smokers (RR=0.97; 95% CI: 0.84-1.14 and RR=1.15; 95% CI: 1.00-1.33, respectively). All meta-analysis findings were of 'very low' to 'low' certainty evidence. Of the studies not included in meta-analysis, we found 'moderate' certainty evidence of higher risk of respiratory symptoms, COPD, asthma, lung inflammation and damage in non-smoker current vapers compared to non-users, inconsistent findings on the risk of COVID-19 and other respiratory infections, and no significant association with e-cigarette associated lung injury.

CONCLUSIONS: E-cigarettes are associated with harms to the respiratory system. Further longitudinal research with special attention to measuring effects in different e-cigarette user populations are warranted.