BIOL PSYC~tqATRY 1990;28:989--996 989 Effects of Bright Light on Resting Metabolic Rate in Patients With Seasonal Affective Disorder and Control Su ects Paul A. Gaist, Eva Obarzanek, Robert G. Skwerer, Connie C. Duncan, Patricia M. Shultz, and Norman E. Rosenthal Many of the symptoms of seasonal affective disorder (SAD) could be construed as having an energy-conserving function. We predicted that SAD patients would have abnormally low resting metabolic rates (RMR), ~vhich would be increased to normal levels by light therapy. To test this hypothesis we measured RMR in 10 patients on and off light treatment and 9 normal controls. Contrary to our prediction we found that SAD patients had significantly higher RMR values compared with the normal population (p < 0.02) and these values were significantly lowered by lig.~t treatment (p < 0.05). The possible implications of these findings are discussed. Introduction To date, several physiological and biochemical abnormalities have been described in seasonal affective disorder (SAD) (Skwerer et al 1988; Depue et al 1990). Bright envi- ronmental light, which has been found to be effective in treating the depressive symptoms of SAD (Lewy et al 1982; Rosenthal et al 1984, 1988), has also been shown to induce changes in a variety of physiological systems (Lewy et al 1980; Skwerer et al 1988). Those systems involved in energy regulation would appear to be of particular relevance in this group of patients, g'~ven the widespread seasonal variation in energy-regulating behaviors described in animals (Dark and Zucker 1985; Mrosovsky 1988; Zucker 1988) and the seasonal variations in energy-regulating physiological functions observed in human subjects (Lacoste and Wirz-Justice 1989). The characteristic torpor of depression has long been compared with hibernation in animals (Lange 1928; K_ripke et al 1978). Indeed, many of the behavioral disturbances typically found in depressed SAD patients, for example, oversleeping, overeating, carbohydrate craving, weight gain, and behavioral withdrawal, could be construed as having an energy conserving function (Rosenthal et al 1986). There have been few studies directed toward examining energy-regulation in nonsea- sonal depressives. Fernstrom et al (1985) found that successful antidepressant treatment From the Clinical Psychobiology Branch (PAG, RGS, PMS, NER), Section on Biomedical Psychiatry (EO), and Laboratory of Psychology and Psychopathology (CCD), NIMH, Bethesda MD. Address reprint requests to Paul A. Gaist, Clinical Psychobiology Branch, NIMH, Bldg. I0/4S-239, 9000 RockviIIe Pike, Bethesda, MD 20892. Received May 12, 1989; revised May 17, 1990. © 1990 Society of Biological Psychiatry 0006-3223/90/$03.50