Melatonin sensitivity to dim white light in affective disorders

Both dim and bright light has been shown to suppress the nocturnal secretio n of the pineal hormone melatonin. Early reports suggests that an abnormal response to light occurs in patients with bipolar affective disorder, where as patients with major depressive disorder respond similarly to controls. It has been suggested that this abnormal sensitivity of the melatonin respo nse to light could be a trait marker of bipolar affective disorder. However reports lack consistency. Hence, we investigated the melatonin suppression by dim light (200 lux) in patients with bipolar affective disorder, season al affective disorder and major depressive disorder. Results suggest that a supersensitive melatonin suppression to light in bipolar affective disorde r (p < .005), and seasonal affective disorder (p < .05), whereas patients w ith major depressive disorder display similar suppression to controls. The supersensitivity may be a mechanism where by phase-delayed rhythms, are re- synchronised to a new circadian position. Conversely, an abnormality may ex ist in the pathway from the retina to the suprachiamatic nucleus. (C) 1999 American College of Neuropsychopharmacology. Published by Elsevier Science Inc.