Iron and attention deficit/hyperactivity disorder: What is the empirical evidence so far? A systematic review of the literature.

The authors systematically reviewed evidence on iron status, as well as studies of iron supplementation, in individuals with attention deficit/hyperactivity disorder (ADHD). PubMed, Ovid, EMBASE and Web of Knowledge were searched on 4 July 2012. Quantitative appraisal of trials was performed using Jadad's score. Most (n = 20) of the retrieved studies assessed an index of peripheral iron status (i.e., serum ferritin), with overall mixed results - that is, both significant and nonsignificant association between ADHD symptoms and serum ferritin levels. One MRI study reported significantly lower indices of thalamic iron in ADHD versus comparison subjects. Two trials, an open-label and a pilot randomized placebo-controlled study with high Jaded score (4), showed improvement in some but not all measures of ADHD symptoms. Three studies showed that children with ADHD plus sleep disorders, in particular restless legs syndrome, are at risk of iron deficiency. Finally, two studies suggested that iron deficiency might decrease the effectiveness of psychostimulant treatment. The authors discussed how the field could move from initial research mainly focused on serum ferritin towards a more comprehensive and translational investigation of iron in ADHD, with the potential to inform clinical practice in terms of screening and treating iron deficiency in individuals with ADHD.