Background: In this research the symptom improvement of attention-deficit hyperactivity disorder (ADHD) of children was assessed by oral vitamin D administration in Tabriz, Iran.

Methods: In this double-blind, randomized clinical trials, 96 children (2-18 years) were enrolled to placebo and vitamin D groups. Children took vitamin D pearl (50,000 IU/week) or placebo for 6 weeks. Children, who had the change in methylphenidate dosage and received any anticonvulsants and corticosteroids were excluded from the research. ADHD symptoms were diagnosed by Conners parent rating scale (CPRS) test at baseline and after intervention. ADHD Conners divided into inattention (IA), hyperactivity/impulsivity (H/I) and combination type (C) subscales. Vitamin D serum level was assessed at baseline and after 8 weeks in both groups.

Results: The differences between CPRS and its subscales were not significant at baseline (P > 0.05). The Conners IA score was decreased in vitamin D group (P < 0.05; adjusted with age and baseline values). ADHD Conners and all subscale scores reduced remarkably after intervention in patients with insufficient level of vitamin D compared to placebo (P < 0.05).