Diurnal profiles of thyroid hormones are altered in depression.

Free thyroxine index (FT4I), serum thyroxine (T4) and thyrotrophin concentrations were measured in 45 depressed subjects and 23 controls. The FT4I am/pm ratio was significantly higher in depressed subjects than in controls. This elevated diurnal ratio of thyroid hormones in depression adds to the literature on the chronobiology of affective disorders, and may help to explain differences in thyroid hormone levels in depressed patients in other studies, where time of sampling has seldom been reported.