Kim JS, et al. - A prospective cohort study was conducted to investigate the prospective association between subclinical hypothyroidism and incident depressive symptoms. Between 1 January 2011 and 31 December 2014, 220,545 middle-age adults without depression who had undergone at least two comprehensive health examinations were enrolled. Using an electrochemiluminescent immunoassay, thyroid-stimulating hormone, free triiodothyronine (FT3), and free thyroxine (FT4) levels were measured. In a large prospective cohort of middle-age men and women, no apparent association was found between subclinical hypothyroidism and incident depressive symptoms.