Prenatal nicotine exposure increases the risk for children developing attention-deficit/hyperactivity disorder (ADHD) later in life, according to study results published in Pediatrics. Higher levels of nicotine were associated with a greater risk for ADHD, investigators reported.

The study included data from 1079 children born in Finland between 1998 and 1999 and diagnosed with ADHD and 1079 age- and gender-matched controls who did not have ADHD. The average age at ADHD diagnosis was 7.3.

Using quantitative immunoassays, investigators measured maternal serum cotinine levels collected from the Finnish Maternity Cohort during the first and early second trimester of pregnancy. Investigators first classified cotinine levels into 3 categories of nicotine exposure: heavy (>50 ng/mL), moderate (20 to 50 ng/mL), and reference (<20 ng/mL). Then investigators distributed cotinine levels into 10 groups by case-control status.

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There was a significant association between increasing maternal cotinine levels and ADHD in offspring. The odds ratio (OR) was 1.09 when adjusting for maternal socioeconomic status, maternal and paternal age, maternal and paternal psychopathology, and child’s birth weight for gestational age. Heavy nicotine exposure was associated with ADHD in offspring in both the unadjusted and adjusted analyses (odds ratio [OR], 2.95 vs OR, 2.21). The strongest association with the risk for ADHD was also in the highest decile (≥90%) in the unadjusted (OR, 4.90) and adjusted analyses (OR, 3.34).

A key question the researchers noted was whether smoking during pregnancy is causally associated with ADHD or is a proxy of another risk factor (eg, familial confounders). However, they concluded, “Even if most of the effect is due to familial or genetic confounding, the current study reveals that the association between smoking and ADHD has a dose-response effect.”

Future research could examine the interplay between maternal smoking and environmental, genetic, and epigenetic factors.

References

Sourander A, Sucksdorff M, Chudal R, et al. Prenatal cotinine levels and ADHD among offspring. Pediatrics. 2019;143(3):e20183144.