Copper in depressive disorder: A systematic review and meta-analysis of observational studies.

Copper (Cu) has been associated with mental disorders such as autism and epilepsy. So far, publications evaluating copper levels in patients with depressive disorder showed conflicted results. To derive a comprehensive estimation of the relationship between body burden of copper and depressive disorder and explore the possible role of copper in mental health, we performed a systematic review and meta-analysis. Relevant published data were obtained by searching PubMed, Web of Science, Chinese National Knowledge Infrastructure (CNKI) and Chinese Biomedical Database (CBM) before October 10, 2017. Weighted mean difference (WMD) with a 95% confidence interval (95%CI) was calculated using STATA 12.0. A total of 21 studies with 1487 patients and 943 controls were collected in this meta-analysis. Pooled analysis found that patients with depression had higher blood levels of copper than the controls without depression, while there was no difference of copper content in hair between the two groups. Subgroup analysis suggested that age had influence on the relationship between copper and depression. No evidence of publication bias was observed. This meta-analysis suggests that increased levels of blood copper might be associated with depressive disorder and therefore the possible role of copper as a biomarker of depression.