Prenatal Secondhand Smoke exposure tied to higher odds of ADHD in Children: JAMA

One recent umbrella review suggested that maternal smoking during pregnancy was strongly associated with the development of ADHD symptoms in their children. When mothers inhale smoke from cigarettes, nicotine distilled from the tobacco is rapidly metabolized in the liver to cotinine, which may disrupt the maturation of the central nervous system, resulting in later development of ADHD symptoms in their offspring.

Although most studies addressing SHS (Secondhand smoke) and ADHD symptoms have evaluated prenatal exposure postnatal SHS exposure may also induce ADHD deficits because the human brain continues to develop during the postnatal period.

Children with different ADHD subtypes experience different symptoms, with subtype-specific effects associated with developing distinct cognitive characteristics, trajectories of symptom persistence, and patterns of comorbidity.

Li-Zi Lin and team of researchers conducted a study to examine the associations of SHS exposure with ADHD symptoms and subtypes in school-aged children by considering the timing of the exposure as published in JAMA network. They hypothesized that the associations between SHS exposure and ADHD symptoms may differ with different exposure timing and among the various subtypes of ADHD symptoms.

The study was a cross-sectional study wherein 48,612 children aged 6 to 18 years from elementary and middle schools in Liaoning province, China, between April 2012 and January 2013 were eligible for participation. Data on SHS exposure and ADHD symptoms and subtypes for each child were collected via questionnaires administered to parents or guardians by school teachers. Data were analyzed from September 14 to December 2, 2020.

The ADHD symptoms and subtypes (inattention, hyperactivity-impulsivity, and combined) were measured based on a validated tool developed from the Diagnostic and Statistical Manual of Mental Disorders. Generalized linear mixed models were evaluated to estimate the association of SHS exposure with ADHD symptoms and subtypes.

Results:

• In the fully adjusted model, compared with their unexposed counterparts, children ever exposed to SHS (OR 1.50) or always exposed to SHS (OR 2.88) had higher odds of ADHD symptoms and higher odds of ADHD subtypes (ORs ranged from 1.46 to 2.94).
• Children with SHS exposure had higher odds of having ADHD symptoms if they were exposed during the prenatal period (OR 2.28), early postnatal period (OR 1.47), or current period (OR 1.20).

• Both prenatal SHS exposure and early postnatal SHS exposure were associated with all ADHD subtypes (ORs ranged from 1.38 to 2.32), whereas current SHS exposure was associated only with the ADHD-I subtype
• Further investigation of current paternal cigarette smoking indicated that, children whose fathers smoked 10 or more cigarettes/day on both weekdays and weekends had higher odds of having ADHD symptoms and subtypes except for the association between weekday paternal cigarette smoking and ADHD-HI symptoms.
• Children with fathers who smoked cigarettes had higher odds of ADHD-HI subtype only when their fathers smoked 5 to <10 cigarettes/d on weekdays.
• When grouping the SHS exposure from pregnancy to childhood into more detailed categories, children in all categories had higher odds of having ADHD or ADHD-I symptoms compared with their unexposed counterparts (ORs ranged from 1.21 to 2.90), whereas the associations of ADHD-HI and ADHD-C symptoms attenuated to the null in several categories.

In this large cross-sectional study, the researchers found that SHS exposure from pregnancy to childhood was associated with ADHD symptoms and subtypes in school-aged children. When considering the timing of the SHS exposure, the associations were more pronounced in the prenatal and early postnatal periods. In addition, children with fathers who smoked cigarettes had higher odds of having ADHD symptoms and subtypes.

The study results indicated that SHS exposure from pregnancy to childhood was associated with higher odds of ADHD symptoms and subtypes in school-aged children, with somewhat stronger associations observed for prenatal and early postnatal periods. The findings highlight the importance of strengthening public health efforts to reduce SHS exposure, which may reduce the health and economic burdens of individuals with ADHD.

"It is important to encourage all adults to avoid smoking, and our results indicated that fathers may be one of the most important target populations to reduce SHS exposure. There is still limited evidence of effective interventions for reducing SHS exposure in children. Pregnancy is considered a reasonable time to help parents who smoke cigarettes to quit. However, few studies have targeted expectant fathers, and current evidence suggests that the behavioral interventions for smoking relapse after birth are not effective. Both fathers and mothers need to be informed of the neurotoxic effects associated with SHS exposure throughout the development of children, and more interventions for smoking cessation are needed."

Source: Li-Zi Lin, PhD; Shu-Li Xu, MM; Qi-Zhen Wu, MM et al ; JAMA Network Open. 2021;4(5):e2110931.

doi:10.1001/jamanetworkopen.2021.10931