Phase of melatonin rhythm in winter depression.

Abstract

Seasonal affective disorder (SAD), winter type, is a relatively recently described syndrome of recurrent episodes of fall-winter depression, fatigue, social withdrawal, oversleeping, overeating, carbohydrate craving and weight gain. Bright light treatment (LT) reverses these symptoms, else they disappear in spring (47). Association of winter depression with reduced day length may suggest that photoperiodic time measurement plays a role in etiology of this disease. LT of the first patient with winter depression (25) was inspired by the facts that, in animals, the day length response is mediated by the circadian rhythm of melatonin (MLT) (14) and, in humans, the exposure to bright light is necessary to suppress MLT secretion (24). However, most investigations argue against the involvement of this hormone in SAD and LT. The reports of the efficacy of midday light (66) were considered to lend no support for the involvement of day length response in SAD pathogenesis and the mechanism by which LT works. MLT administered orally in the morning and early evening did not completely reverse the effects of LT, although it did reproduce the atypical depressive symptoms of SAD (social withdrawal, hyperphagia, appetite and weight increase, carbohydrate craving, hypersomnia, fatigability and reverse diurnal variations) (49). In another study (73), MLT given to SAD patients either in the morning or in the evening had no effect on depressive symptoms, while bright light did.