Our study demonstrated that there was no significant difference in serum zinc between depressed and non-depressed subjects, but ORs (95% CI) of depression were 1.35(1.077–1.692) and 1.016(1.005–1.027) in lowest serum copper quartile versus quartiles 2, 3 combined and for serum hs-CRP respectively. The association between zinc to copper ratio, PAB, SOD and depression was not statistically significant.
Similar to our study, in a case control study of 88 depressive patients and 88 volunteers, median serum zinc concentration in depressive patients did not differ from control group(Irmisch, Schlaefke, & Richter, 2010). Our findings were in a good agreement with other studies. Gronli et al. showed that in different psychiatric diagnoses, patients who were not depressed had a higher prevalence of zinc deficiency (Grønli et al., 2013).
Narang et al. illustrated that the mean plasma zinc levels in controls and depressed patients were not significantly different(Narang, Gupta, Narang, & Singh, 1991).
In a placebo-controlled, double blind study, sixty patients, 18-55-year old, received antidepressant and either placebo or zinc supplementation. This study obtained no significant difference in the BDI scores between case and control groups(Siwek et al., 2009).
Several studies have shown an association between zinc deficiency and depression (Maes et al., 1997; Marcellini et al., 2006; Siwek et al., 2010).
In contrast to our study, such inconsistencies may be due to the fact that we studied people with depressive symptoms, rather than a clinical diagnosis of depressive disorder.
Therefore, there is still some ambiguity in the role of serum zinc in depression (Styczeń et al., 2017).
Our study also showed that the mean depression score for those with lowest quartile of copper was significantly higher than highest quartile. In a population based study of 14834 American adults, the daily intake of copper in participants with depression were significantly lower than those without depression. The roles of copper in depression are not well established and future researches are needed to explore the underlying mechanisms(Li, Wang, Xin, Song, & Zhang, 2018).
A case-control study in Korean adolescent girls illustrated an inverse relationship between copper intake and depression(Kim, Choi, Lee, & Park, 2015). It is also shown that Copper supplement may reduce anxiety and depression during pregnancy(Kashanian et al., 2018).
In contrast to our study, some researches showed that patients with depression have higher levels of blood copper, even after antidepressant treatment(Russo, 2011; Schlegel-Zawadzka et al., 1999).
However the roles of copper in depression are not well established and further research is needed to explore the underlying mechanisms(Li et al., 2018). The association between SOD and depression was not statistically significant in the present study. Some studies showed raising of SOD activity in schizophrenia, bipolar mood disorder and major depression(Kodydková et al., 2009; Kunz et al., 2008), while in one study the activity of SOD was low in bipolar depressive episode(Selek et al., 2008).
Studies have showed a possible pathophysiological role of oxidative and antioxidative molecules in many neuropsychiatric disorders(Bilici et al., 2001; Selek et al., 2008). In some studies serum SOD activity were reported to be raised in schizophrenia, bipolar mood disorder and major depression; in contrast in another study the activity of SOD was low in bipolar depressing episode(Selek et al., 2008).
CRP levels were associated with symptoms of depression in our participants which is consistent with previous findings (Elovainio et al., 2009; Liukkonen et al., 2006; Wium-Andersen & Nielsen, 2013). Studies have suggested link between oxidative stress and serval mental disorders such as depression, anxiety disorders, schizophrenia and bipolar disorder(Ng, Berk, Dean, & Bush, 2008; Salim, 2014). In our depressed participants, serum PAB was higher in comparison to the non-depressed, but after multivariate-adjusted analysis this value was no longer significant.
A major strength of this study was a large sample size. Since, our study has a cross-sectional design, it is difficult to make causal inference, and our sample was limited to male subjects only.
In conclusion, our results indicated that there was no significant difference in serum zinc content between depressed and non-depressed subjects. Lowest copper quartile versus highest quartile and hs-CRP, were positively associated with depression. The association between zinc to copper ratio, PAB, SOD and depression was not statistically significant. However due to cross-sectional design, we could not prove causality relationship. Future studies are needed to confirm these findings.