Zinc monotherapy increases serum brainderived neurotrophic factor (BDNF) levels and decreases depressive symptoms in overweight or obese subjects: A double-blind, randomized, placebo-controlled trial

Objective: Previous studies have shown a positive effect of zinc as an adjunctive therapy on reducing depressive symptoms. However, to our knowledge, no study has examined the effect of zinc monotherapy on mood. The aim of the present study was to determine the effects of zinc monotherapy on depressive symptoms and serum brain-derived neurotrophic factor (BDNF) levels in overweight or obese subjects. Methods: Fifty overweight or obese subjects were randomly assigned into two groups and received either 30 mg zinc or placebo daily for 12 weeks. At baseline and post-intervention, depression severity was assessed using Beck depression inventory II (BDI II), and serum BDNF and zinc levels were determined by enzyme-linked immunosorbent assay and atomic absorption spectrophotometry, respectively. Results: The trial was completed with 46 subjects. After a 12-week supplementation, serum zinc and BDNF levels increased significantly in the zinc-supplemented group compared with the placebo group. BDI scores declined in both the groups at the end of the study, but reduction in the zinc-supplemented group was significantly higher than the placebo group. More analysis revealed that following supplementation, BDI scores decreased in subgroup of subjects with depressive symptoms (BDI >= 10) (n= 30), but did not change in the subgroup of non-depressed subjects (BDI < 10) (n= 16). Moreover, a significant inverse correlation was observed between serum BDNF levels and depression severity in all participants. Interestingly, a significant positive correlation was found between serum BDNF and zinc levels at baseline. Conclusion: Zinc monotherapy improves mood in overweight or obese subjects most likely through increasing BDNF levels.