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Maternal smoking indirectly influences offspring mental illness
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Recent findings failed to show a causal association between maternal smoking and severe mental illness in offspring, but indicated it may be attributed to factors shared by siblings.
“Maternal smoking during pregnancy is associated with a breadth of adverse offspring outcomes, including pregnancy-related, neurodevelopmental, and behavioral problems. In particular, recent studies have provided novel evidence of associations between [smoking during pregnancy] and offspring bipolar disorder, schizophrenia, and related outcomes,” Patrick D. Quinn, PhD, of Indiana University, Bloomington, and colleagues wrote. “These associations raise the possibility that [smoking during pregnancy] exposure has causal teratogenic effects on the risk of severe mental illness.”
To determine associations between smoking during pregnancy and severe mental illness in offspring, researchers analyzed population register data for 1,680,219 individuals born in Sweden from 1983 through 2001.
Rates of severe mental illness were higher among offspring exposed to moderate (HR = 1.25; 95% CI, 1.19-1.3) and high (HR = 1.51; 95% CI, 1.44-1.59) levels of smoking during pregnancy compared with unexposed offspring.
Strength of these associations decreased with increasing statistical and methodologic controls for familial confounding, according to researchers.
Sibling comparisons with within-family covariates indicated notably weaker and nonsignificant associations for moderate (HR = 1.09; 95% CI, 0.94-1.26) and high levels (HR = 1.14; 95% CI, 0.96-1.35) of smoking during pregnancy.
This pattern was consistent across subsets of severe mental illness disorders and supported by further sensitivity analyses.
“The Quinn et al results are relatively convincing. The [smoking during pregnancy]-[severe mental illness] association is substantially attenuated with measured confounders and discordant cousin pairs. The attenuation is even greater in sibling pairs and loses statistical significance,” Kenneth S. Kendler, MD, of Virginia Commonwealth University, wrote in an accompanying editorial. “In a lovely move, they used the co-relative design to show that the impact of [smoking during pregnancy] on two obstetric outcomes (small for gestational age and preterm birth) attenuates much less in relative pairs than [severe mental illness] and so is likely a true consequence of [smoking during pregnancy].”
However, Kendler warned “we can never be certain about causal processes” based on observational data. Thus, these findings should be taken with that consideration in mind. – by Amanda Oldt
Disclosure: Quinn reports no relevant financial disclosures. Please see the study for a full list of relevant financial disclosures.