The association between thyroid hormone levels and psychiatric symptoms in patients with mania or depression

Thyroid hormones play a crucial role in regulating mood and cognitive function. However, the effect of thyroid function on psychiatric symptoms remains unclear. In this study, we investigated the association between psychiatric symptoms and thyroid hormone levels in patients with depression and mania. In this retrospective cross-sectional study, we enrolled patients with depression or mania admitted to the Department of Psychiatry of the National Kohnodai Medical Center from April 2014 to March 2023. We examined the association between thyroid function at admission and psychiatric symptoms using the Global Assessment of Functioning (GAF) score. A total of 309 patients with depression (199 females, mean age = 62 ± 15 years) and 91 patients with mania (60 females, mean age = 50 ± 16 years) were included. In the depression group, the median TSH level was 1.05 μIU/mL, the median free T3 level was 2.76 pg/mL, and the median free T4 level was 0.95 ng/dL. In the mania group, the median TSH level was 1.09 μIU/mL, the median free T3 level was 3.28 pg/mL, and the median free T4 level was 1.06 ng/dL. In patients with depression, the GAF score showed a weak but significant negative correlation with the free T4 level (r = -0.212, p < 0.001) and with the free T3 level (r = -0.253, p = 0.008). In patients with mania, the GAF score was negatively correlated with the free T4 level (r = -0.225, p = 0.033) and positively correlated with the TSH level (r = 0.226, p = 0.031). These findings suggest that higher thyroid hormone levels may be associated with more severe psychiatric symptoms. Our study presents possible associations between thyroid hormone levels and psychiatric symptoms.