TPO and major depressive disorder: Ittermann et al. in 2015 conducted a study on 2142 individuals who followed the Study of Health in Pomerania (SHIP-1) and the Life Events and Gene-Environment Interaction in Depression study (LEGEND) to investigate the association between diagnosed thyroid disorders, serum TSH levels, and anti-thyroid-peroxidase antibodies (TPOAbs) with depression and anxiety.