Secondhand smoke exposure increases risk for ADHD symptoms among school-aged children

Secondhand smoke exposure between the prenatal period and childhood increased risk for having ADHD symptoms and subtypes among school-aged children, according to results of a cross-sectional study published in JAMA Network Open.

Researchers noted somewhat stronger associations for secondhand smoke exposure during prenatal and early postnatal periods.

“Although most studies addressing [secondhand smoke] and ADHD symptoms have evaluated prenatal exposure, postnatal [secondhand smoke] exposure may also induce ADHD deficits because the human brain continues to develop during the postnatal period,” Li-Zi Lin, PhD, of the Guangdong Provincial Engineering Technology Research Center of Environmental Pollution and Health Risk Assessment at Sun Yat-sen University in China, and colleagues wrote. “Among studies considering both prenatal and postnatal [secondhand smoke] periods, [three] cohort studies and [one] case-control study suggested that [secondhand smoke] exposure from pregnancy to childhood was associated with ADHD symptoms. However, those studies were unable to distinguish between the postnatal exposure during early childhood and later childhood.”

Lin and colleagues aimed to assess potential links between ADHD symptoms/subtypes and prenatal, early postnatal or current secondhand smoke exposure among 45,562 children (50.3% girls; mean age, 11 years; 4.8% with ADHD symptoms) aged 6 to 18 years from elementary and middle schools in a province in China between April 2012 and January 2013. They used questionnaires given to parents or guardians by schoolteachers to collect data on each child’s secondhand smoke exposure and ADHD symptoms and subtypes. They used a validated tool developed via the DSM-4 to measure ADHD symptoms and subtypes, including inattention, hyperactivity-impulsivity and combined. Further, they estimated the link between secondhand smoke exposure and ADHD symptoms and subtypes by conducting an evaluation of generalized linear mixed models.

Results showed increased risk for having ADHD symptoms and subtypes, with ORs ranging from 1.46 (95% CI, 1.31-1.62) to 2.94 (95% CI, 2.09-4.13), among children who were ever exposed (IR = 1.5; 95% CI, 1.36-1.66) or always exposed (OR = 2.88; 95% CI, 2.55-3.25) to secondhand smoke between the prenatal period and childhood compared with their unexposed counterparts. Those with secondhand smoke exposure had increased risk for having ADHD symptoms when exposed in the prenatal period (OR = 2.28; 95% CI, 2.07-2.51), early postnatal period (OR = 1.47; 95% CI, 1.29-1.68) or current period (OR = 1.2; 95% CI, 1.09-1.31) compared with their unexposed counterparts. Those whose fathers smoked at least 10 cigarettes per day on both weekdays and weekends had increased risk for having ADHD symptoms and subtypes, with ORs ranging from 1.48 (95% CI, 1.28-1.7) to 2.25 (95% CI, 1.29-3.93), compared with their unexposed counterparts.

“Our findings highlight the importance of strengthening public health efforts to reduce [secondhand smoke] exposure, which may reduce the health and economic burdens of individuals with ADHD,” Lin and colleagues wrote.