Estimating causal and time-varying effects of maternal smoking on youth smoking

Abstract

Introduction: Maternal smoking is a well-known risk factor for youth smoking, yet whether this relationship is causal remains unresolved. This study utilizes propensity score methods for causal inference to robustly account for shared risk factors between maternal and offspring smoking.

Methods: An 8-year longitudinal cohort of 900 adolescents in the Chicago area were followed starting from approximately age 15.6. The effects of maternal lifetime smoking (MLS) and prenatal tobacco exposure (PTE) (among participants reporting MLS) on offspring's past 30-day smoking, daily smoking status and smoking frequency were examined using logistic regression and Poisson regression after nearest-neighbor propensity matching. Age dependency of this relationship was then examined across the age range of 15-25 using time-varying effect modeling.

Results: Propensity matching yielded 438 and 132 pairs for MLS and PTE study samples, respectively. MLS demonstrated significant associations with past 30-day smoking (RR 1.09; 95% CI 1.04-1.14), daily smoking (RR 1.08; 95% CI 1.05-1.12), and smoking frequency of offspring (RR 1.32; 95% CI 1.15-1.52), with stable effects across age. Among participants reporting MLS, having PTE showed significant additional effects on daily smoking (RR 1.09; 95% CI 1.02-1.17) and age-dependency that showed significance during young adulthood but not adolescence.

Conclusion: The relationship between maternal and offspring smoking was not fully accounted for by shared risk factors, suggesting possible causation with PTE having a delayed effect across age. Targeted prevention efforts should be made on maternal smoking-exposed adolescents to mitigate their risks of developing heavy smoking habits in adulthood.

Keywords: Adolescent; Maternal smoking; Offspring; Prenatal tobacco exposure; Smoking.

Figure 1.

Flowchart of the sample by analytic stages

Figure 2.

Age-varying effects of maternal lifetime smoking on offspring’s smoking status Note: The y-axis represents the strength (risk ratio) of the association between maternal lifetime smoking and current (Figure 1a) or daily (Figure 1b) smoking status of offspring. The central solid line indicates the point estimate of the risk ratio, and the gray ribbon with dashed borders shows the 95% confidence interval. The horizontal line shows the risk ratio of 1 (no predictive validity).

Figure 3.

Age-varying effects of prenatal tobacco exposure on offspring’s smoking status, in participants with positive maternal lifetime smoking history Note: The y-axis represents the strength (risk ratio) of the association between prenatal tobacco exposure and current (Figure 2a) or daily (Figure 2b) smoking status of offspring. The central solid line indicates the point estimate of the risk ratio, and the gray ribbon with dashed borders shows the 95% confidence interval. The horizontal line shows the risk ratio of 1 (no predictive validity).