CONFERENCE PROCEEDING
Impact of secondhand tobacco smoke on lung function and respiratory symptoms in never-smokers: A systematic review and meta-analysis
1
Preventive Medicine and Public Health, University of Santiago de Compostela, Santiago de Compostela, Spain
2
Respiratory Department, Hospital Universitario Álvaro Cunqueiro, Vigo, Spain
3
CICS-UBI Health Sciences Research Center, University of Beira Interior and CHCB University Hospital, Covilhã, Portugal
4
Respiratory Department, Complexo Hospitalario Universitario de A Coruña, A Coruña, Spain.
Tob. Prev. Cessation 2026;12(Supplement 1):A46
ABSTRACT
BACKGROUND-AIM:
Secondhand tobacco smoke (SHS) contains multiple carcinogens and is a recognized cause of respiratory disease. Although the prevalence of SHS exposure is declining globally, several population groups remain exposed. Evidence on the respiratory effects of SHS exposure in never-smokers is inconsistent and often with methodological limitations. This study aimed to summarise the available evidence on the association between SHS exposure and lung function and respiratory symptoms in adults who have never smoked.
METHODS:
A systematic review with meta-analysis was conducted following PRISMA 2020 guidelines. A bibliographic search was performed in PubMed, EMBASE and Web of Science (November 2024; updated July 2025). Observational studies evaluating SHS exposure in adult never-smokers and reporting lung function parameters or respiratory symptoms were included. Data extraction and quality assessment were performed by peers. Random-effects meta-analyses were conducted when there were at least 3 studies were available. Heterogeneity was assessed using I², and sensitivity analyses and publication bias tests were performed.
RESULTS:
Twenty-seven studies (n=135363 participants; 67.4% never-smokers) conducted in 17 countries met inclusion criteria. SHS exposure was significantly associated with impaired lung function. Meta-analyses showed a decreased predicted FEF25–75 (mean difference −5.92%; 95%CI −10.49 to −1.35; I² = 0.00%, p=0.76) and FEV1/FVC ratio (−2.52%; 95%CI −4.32 to −0.73; I2 = 58.97%, p= 0.09) in exposed individuals. No significant pooled differences were observed for other spirometric parameters. Sensitivity analyses indicated that the results were influenced by studies with high-intensity occupational exposure. SHS exposure was associated with an increased risk of respiratory symptoms, such as cough (OR 1.44; 95%CI 1.19–1.73; I² = 24.58%, p = 0.27) and dyspnea (OR 1.41; 95%CI 1.17–1.70; I² = 16.19%, p = <0.01). The association with wheezing was borderline significant (OR 1.75; 95%CI 1.01–3.04; I² = 90.29%, p = <0.01), with high heterogeneity. No significant association was found for sputum. Overall studies quality was low to moderate, mainly due to limited exposure characterization. Publication bias test does not suggest publication bias for any of the analyses.
CONCLUSIONS:
Exposure to SHS is associated with reduced lung function, particularly with regard to markers of small airway dysfunction (FEF25–75 and FEV1/FVC), and increased risk of respiratory symptoms in never-smoking adults. These findings highlight the need to support the strengthening of public health policies aimed at reducing involuntary exposure to
Secondhand tobacco smoke (SHS) contains multiple carcinogens and is a recognized cause of respiratory disease. Although the prevalence of SHS exposure is declining globally, several population groups remain exposed. Evidence on the respiratory effects of SHS exposure in never-smokers is inconsistent and often with methodological limitations. This study aimed to summarise the available evidence on the association between SHS exposure and lung function and respiratory symptoms in adults who have never smoked.
METHODS:
A systematic review with meta-analysis was conducted following PRISMA 2020 guidelines. A bibliographic search was performed in PubMed, EMBASE and Web of Science (November 2024; updated July 2025). Observational studies evaluating SHS exposure in adult never-smokers and reporting lung function parameters or respiratory symptoms were included. Data extraction and quality assessment were performed by peers. Random-effects meta-analyses were conducted when there were at least 3 studies were available. Heterogeneity was assessed using I², and sensitivity analyses and publication bias tests were performed.
RESULTS:
Twenty-seven studies (n=135363 participants; 67.4% never-smokers) conducted in 17 countries met inclusion criteria. SHS exposure was significantly associated with impaired lung function. Meta-analyses showed a decreased predicted FEF25–75 (mean difference −5.92%; 95%CI −10.49 to −1.35; I² = 0.00%, p=0.76) and FEV1/FVC ratio (−2.52%; 95%CI −4.32 to −0.73; I2 = 58.97%, p= 0.09) in exposed individuals. No significant pooled differences were observed for other spirometric parameters. Sensitivity analyses indicated that the results were influenced by studies with high-intensity occupational exposure. SHS exposure was associated with an increased risk of respiratory symptoms, such as cough (OR 1.44; 95%CI 1.19–1.73; I² = 24.58%, p = 0.27) and dyspnea (OR 1.41; 95%CI 1.17–1.70; I² = 16.19%, p = <0.01). The association with wheezing was borderline significant (OR 1.75; 95%CI 1.01–3.04; I² = 90.29%, p = <0.01), with high heterogeneity. No significant association was found for sputum. Overall studies quality was low to moderate, mainly due to limited exposure characterization. Publication bias test does not suggest publication bias for any of the analyses.
CONCLUSIONS:
Exposure to SHS is associated with reduced lung function, particularly with regard to markers of small airway dysfunction (FEF25–75 and FEV1/FVC), and increased risk of respiratory symptoms in never-smoking adults. These findings highlight the need to support the strengthening of public health policies aimed at reducing involuntary exposure to
| eISSN: | 2459-3087 |
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