TG and major depressive disorder: Statistical analysis revealed a significant difference in the proportion of subjects with normal levels of thyroid hormones (TSH, FT3, FT4) between the two groups (χ2 = 14.41, df = 1, p < 0.0001), with 75.38% (n = 395) of the MDD patients and 83.47% (n = 833) of the HCs having normal levels of thyroid hormones.