Blood and hair zinc levels in children with attention deficit hyperactivity disorder: A meta-analysis

We summarized the observational studies on the correlation between zinc and attention deficit hyperactivity disorder (ADHD) since 1986, extracted relevant data for meta-analysis to determine the relationship between zinc and ADHD. We searched PubMed, Scopus, Cochrane Library, EMBASE (included EMBASE and Medline), Web of Science and Clinical Trials.gov databases from inception to April 8, 2019. We assessed the blood zinc, hair zinc and ADHD by combined the standardized mean difference (SMD) and 95% confidence interval (CI). Statistical analysis was performed using Stata 14.0. We included 11 studies for meta-analysis. Of these, 8 studies comprising 1311 participants reported blood zinc and 3 studies comprising 206 participants reported hair zinc. The zinc levels in blood (SMD: -0.91, 95% CI: -1.88-0.07, P(SMD) < 0.068), and hair (SMD: 1.42, 95% CI: -4.49-7.33, P(SMD) = 0.638) not significantly compare ADHD with controls. Nevertheless, high heterogeneity (I2 > 97.3%) emerged among the included studies. The subgroup analysis showed that the heterogeneity of samples >100 group was significantly reduced. The sensitivity analysis found that the results changed significantly after excluding the only cross-sectional study. In conclusion, our meta-analysis showed that there was no statistically significant difference in blood zinc and hair zinc levels between ADHD children and adolescents compared with healthy children and adolescents.