There is evidence from epidemiological studies that low levels of zinc are associated with depression, but good quality clinical trials that explore the link between zinc supplementation and depression are few and far between.
This systematic review conducted by a research team from the University of Newcastle in New South Wales, Australia, aimed to synthesise results from all published randomised controlled trials (RCT) on the efficacy of zinc supplementation for reducing or preventing depressive symptoms.
The authors searched a range of databases, looking for RCTs with a comparison group, that examined zinc supplementation as the intervention and depressive symptoms as the primary outcome. They found just 4 trials that met their inclusion criteria and were not able to pool the results of these studies because there was substantial heterogeneity (i.e. the trials were too different from one another to be grouped together in a meta-analysis).
However, the research team did find that in the studies that investigated treating depression with zinc supplementation and antidepressants, zinc significantly lowered depressive symptom scores of depressed patients.
The authors went on to report that there was less clear evidence on the effectiveness of zinc supplementation alone on depressive symptoms of non-depressed healthy subjects.
The authors concluded:
Evidence suggests potential benefits of zinc supplementation as a stand-alone intervention or as an adjunct to conventional antidepressant drug therapy for depression. However, there are methodological limitations in existing studies and so further well-designed, adequately powered research is required.
Lai J, Moxey A, Nowak G, Vashum K, Bailey K, McEvoy M. The efficacy of zinc supplementation in depression: Systematic review of randomised controlled trials. J Affect Disord. 2011 Jul 26. [Epub ahead of print] [PubMed abstract]