Many studies have examined the association between parental age and psychiatric illness in the children, including autism and schizophrenia. In a recent case-control study from Finland, the authors identified 10,409 individuals with ADHD born between 1991 and 2005 from nationwide population-based registers. Logistic regression was used to examine the association between parental age and ADHD in the offspring, adjusting for potential confounding factors including parental psychiatric history, maternal socioeconomic status, marital status, maternal smoking during pregnancy, number of previous births, and birth weight.
The researchers found that fathers younger than 20 years had a 1.5-fold (OR=1.55, 95% CI: 1.11-2.18, p=.01) increased risk of having offspring with ADHD as compared to fathers aged 25-29 years. Similarly mothers younger than 20 years had a 1.4-fold (OR= 1.41, 95% CI: 1.15-1.72, p =.0009) increased risk. Advanced maternal age was inversely associated with ADHD (OR=0.79, 95% CI: 0.64-0.97, P=.02). When both parents were younger than 20 years, the risk of having a child with ADHD was nearly doubled (OR=1.94).
While this finding has statistical significance, we must be careful in interpreting its results. Parents who have children at a younger age may be more likely to have ADHD themselves than older parents; thus, this finding may be driven by genetic factors more than parental age. In addition, younger parents face many stressors, including poverty and lack of social supports, which may modulate risk for ADHD in the children.
In an earlier study, researchers analyzed data from Swedish national registers of all children born between 1988 and 2003, including 30,674 children with ADHD. This study used sibling- and cousin-comparisons to control for unmeasured genetic and environmental confounding. Maternal age of <20 years) associated with 78% increased risk of ADHD; however, the association attenuated in cousin-comparison, suggesting unmeasured familial confounding. The analysis of siblings indicated that the association between maternal age and ADHD was mainly explained by genetic confounding.
Whatever is behind this finding, this study argues that the children of younger parents may benefit from certain interventions to decrease their risk of ADHD.
Ruta Nonacs, MD PhD
Chang Z, Lichtenstein P, D’Onofrio BM, et al. Maternal age at childbirth and risk for ADHD in offspring: a population-based cohort study. Int J Epidemiol. 2014 Dec;43(6):1815-24.
Chudal R, Joelsson P, Gyllenberg D, et al. Parental Age and the Risk of Attention-Deficit/Hyperactivity Disorder: A Nationwide, Population-Based Cohort Study. J Am Acad Child Adolesc Psychiatry 2015.