Shih JH, et al. - Researchers performed an electronic search on databases including PubMed, ProQuest, ClinicalKey, Cochrane Library, ClinicalTrials.gov, Embase, Web of Science, and ScienceDirect, with the last search on March 25, 2018, to examine the relationship between peripheral manganese levels and attention-deficit/hyperactivity disorder (ADHD) in children. For this meta-analysis, human observational studies examining peripheral manganese levels in children with ADHD and controls were incorporated. Manganese levels were significantly higher in ADHD children than in controls when studies investigating blood levels and those investigating hair levels were included. However, when only studies investigating blood levels were included, there was no significant difference between ADHD children and controls. Still, our results support higher peripheral manganese levels are found in children diagnosed with ADHD vs those in controls.