Differences in respiratory wheezing between current exclusive e-cigarette users, current exclusive cigarette smokers, and never users of either product: findings from a population-based study

Background E-cigarettes have emerged as an alternative to combustible cigarettes, yet their comparative impact on respiratory symptoms remains uncertain. We investigated cross-sectional differences in self-reported wheezing between current exclusive e-cigarette users, current exclusive cigarette smokers, and never-users of either product. Methods We analysed data from 9000 adults aged ≥ 16 years in the 2017–2019 Scottish Health Survey. The exposure was current nicotine use status (exclusive cigarette smoking, exclusive e-cigarette use, or never-use), and the outcome was self-reported wheezing in the past 12 months. Binary multivariable logistic regression estimated adjusted odds ratios (ORs) with 95% confidence intervals (CIs), controlling for age, sex, area-level socioeconomic deprivation, longstanding illness, doctor-diagnosed asthma and COPD, self-rated general health, alcohol consumption, age of smoking initiation, and exposure to second-hand smoke. Results Compared to exclusive e-cigarette users, exclusive cigarette smokers had significantly higher odds of wheezing (adjusted OR = 1.80, 95% CI: 1.33–2.42, p < 0.001). Never-users had lower odds of wheezing than exclusive e-cigarette users, though the difference was not significant (adjusted OR = 0.66, 95% CI: 0.31–1.40, p = 0.275). Among exclusive cigarette smokers, the odds of wheezing increased with smoking intensity relative to exclusive e-cigarette users, indicating a dose-response relationship (χ² = 5.91, p = 0.018). Specifically, light smokers (< 10 cigarettes/day) had elevated but not significant odds (adjusted OR = 1.32, 95% CI: 0.92–1.89, p = 0.133), while moderate smokers (10–19 cigarettes/day) showed higher odds (adjusted OR = 1.85, 95% CI: 1.33–2.59, p < 0.001), and heavy smokers (≥ 20 cigarettes/day) had the greatest odds (adjusted OR = 2.27, 95% CI: 1.57–3.28, p < 0.001). Adjusted predicted probabilities of wheezing mirrored this pattern: compared with exclusive e-cigarette users, probabilities weresignificantly higher for moderate smokers (+ 7.2%, p = 0.002) and heavy smokers (+ 10.0%, p < 0.001), but not for light smokers (+ 3.0%, p = 0.152) or never-users (–3.9%, p = 0.306). Conclusions Exclusive e-cigarette use was not associated with higher odds of wheezing compared with never-use, and it was linked to substantially lower odds than exclusive cigarette smoking. These findings suggest that, while complete abstinence remains the lowest-risk option, e-cigarette use may pose fewer respiratory symptoms than smoking, particularly for moderate-to-heavy smokers.