ADHD Risk Increases for Firstborn Children with Siblings

Nicole Wolff, PhD

Firstborn children may be at a higher risk of attention deficit hyperactivity disorder (ADHD) if younger siblings are born during the developmental stage of ADHD, according to research published in the Journal of Attention Disorders. The study found that reduction of parental resources and increased levels of personal responsibility among older siblings during the developmental period may play a role in this risk.

“This may be the first study examining the association between birth order and number of siblings with ADHD,” according to leading researcher Nicole Wolff, PhD, of TU Dresden in Dresden, Germany. “Other studies have shown similar findings, but these made broader statements, included additional family structure components, and did not adjust for common ADHD risk factors that we included in our study.”

The German cross-sectional National Health Interview and Examination Survey for Children and Adolescents (KiGGS) study was used to obtain patient data for this sub-study analysis. A total of 13,488 pediatric subjects were chosen from the KiGGS, of whom 660 had an ADHD diagnosis. The researchers collected information on the birth order of participants, correlating these data with ADHD diagnoses during the vulnerable stage of ADHD development.

In the cohort, male participants had a higher chance of receiving an ADHD diagnosis compared with females (χ2 = 246.45, df = 1, P <.001). Firstborn children with siblings were significantly more likely to have received an ADHD diagnosis compared with children with no siblings (single child; odds ratio [OR] 1.31, 95% CI 1.03-1.68]). This association persisted when researchers compared firstborn children with youngest-born participants with siblings (>1 child; OR 1.31, 95% CI 1.09, 1.58).

The regression analysis, which controlled for confounders such as age and sex, socioeconomic status, maternal age at childbirth, duration of breastfeeding, and low birth weight/premature birth, found that the association between firstborns with siblings and higher ADHD risk compared with children without siblings remained stable (OR 1.55; 95% CI 1.09-2.21). Firstborns also had higher rates of ADHD compared with youngest children with siblings (OR 1.37, 95% CI 1.06-1.76).

Researchers also observed that ADHD risk was significantly higher among firstborn children with ≥2 younger siblings vs children with no siblings (OR 1.71; 95% CI 1.08-2.69). Additionally, there was a 1.52 times higher risk for ADHD among children with only 1 younger sibling vs children with no siblings (95% CI 1.05-2.19).

Considering identification of ADHD was based primarily on self-report rather than standard clinical diagnostic criteria, it’s likely that some participants in the non-ADHD group may have met these clinical criteria. The lack of ADHD subtype analyses also precludes the ability to know whether these findings are consistent when applied to specific disorders within the ADHD spectrum.

“Professionals might benefit from focusing more intensively on the subjective meaning of having younger siblings, for example, regarding individual etiology models when treating ADHD,” the researchers wrote. “Moreover, a focus on specific family interactions between siblings and establishing, for example, specific play time for the affected child, may be promising treatment targets and focus of further research.”

The study, “Siblings and Birth Order—Are They Important for the Occurrence of ADHD?” was published in the Journal of Attention Disorders.