Since it has been found that changes in glucose metabolism occurring in depression are normalized by clinically effective adjunctive therapy with levothyroxine (L-T4) or T3, it is therefore possible that one of the causes of depression may be a weakening of the metabolic effects of thyroid hormones in the brain (Iosifescu et al., 2008; Bauer et al., 2010, 2016). Here, TG is linked to major depressive disorder.