Meta-Analysis of the Association Between Secondhand Smoke Exposure and Physician-Diagnosed Childhood Asthma

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Studies suggest an association between secondhand smoke exposure and the development of childhood asthma. Several countries are considering legislation to protect children from exposure.


A systematic review was conducted using MEDLINE, Embase, PubMed, and Web of Knowledge databases and a random effects meta-analysis was undertaken. Heterogeneity was assessed using the I2 test. Publication and small study biases were examined visually using a funnel plot and tested formally using Egger test. Univariate and multivariate meta-regression analyses were undertaken, including a subgroup analysis of cohort studies to examine the effect of duration of follow-up.


Twenty relevant studies were identified (14 cross-sectional, 4 cohort, and 2 case–control) and provided 31 estimates of effect size. The pooled odds ratio was 1.32 (95% CI: 1.23, 1.42, p < .001). There was moderate heterogeneity (I2 = 74.2%, p < .001). On multivariate meta-regression analysis, effect size estimates were significantly higher for case–control studies (p = .042) and those using self-reported exposure to secondhand smoke (p = .050). There was no evidence of significant publication or small study bias (Egger test, p = .121).


There is now consistent evidence of a modest association between secondhand smoke and physician-diagnosed childhood asthma. These results lend support to continued efforts to reduce childhood exposure to secondhand smoke.

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