Seasonal Influence on the Dexamethasone Suppression Test Results in Unipolar Depression

To the Editor.—  In the "contemporary confusion" of the psychiatric use of the dexamethasone suppression test (DST),¹ in addition to the numerous confounding factors (eg, acute hospitalization, weight loss, age, severity, etc), one further possible source of controversy should be considered. Seasonal influence has been reported not only for the incidence of affective disorders,² but also for neurochemical and neuroendocrine parameters that are related to the pathophysiology of affective disorders.^3,4 Recent findings —the inverse correlation between cortisol and melatonin secretion⁵ and more frequent occurrence of depression during the summer in DST nonsuppressors with low melatonin syndrome⁶—suggest a seasonal variation in the DST results.The DST was performed on 216 depressed inpatients who met the Research Diagnostic Criteria for the recurrent unipolar major depressive disorder. A single oral dose of 1 mg of dexamethasone was given at 10 PM. Blood samples were taken on the