Serum ferritin and ADHD in children: a case-control study accounting for inflammation

Abstract

To evaluate the association between serum ferritin (SF) and attention-deficit/hyperactivity disorder (ADHD) in children while accounting for C-reactive protein (CRP). This retrospective case-control study included 156 children with DSM-5 ADHD and 164 healthy controls aged 6–12 years identified from hospital records. Iron indices, CRP, and hematologic parameters were extracted. Iron deficiency was defined as SF < 30 µg/L. Logistic regression, restricted cubic splines, and population attributable risk fraction were used. Median SF was lower in ADHD than controls (24.6 vs. 35.8 µg/L; P < 0.001), and iron deficiency was more common (42.3% vs. 18.9%; P < 0.001). After adjustment for age, sex, BMI, CRP, parental education, ADHD family history, picky eating, and meat intake, iron deficiency remained associated with ADHD (adjusted OR = 2.45, 95% CI: 1.58–3.80). After excluding children with CRP ≥ 10 mg/L, the association remained (adjusted OR = 2.78, 95% CI: 1.74–4.44). Spline analysis showed increased ADHD odds below SF 30 µg/L; the fully adjusted model-based attributable risk fraction was 19.7%. Lower SF levels show a correlational association with ADHD after accounting for inflammatory status. Due to the case-control design, whether iron deficiency precedes ADHD or results from ADHD-related dietary behaviors cannot be determined. Ferritin interpreted alongside CRP may help characterize iron status in children evaluated for ADHD, although prospective longitudinal and interventional studies are needed to clarify directionality and clinical relevance.