Delivered by Publishing Technology to: Oulun Yliopisto (University of Oulu) IP: 130.231.240.27 On: Thu, 22 May 2014 07:21:22 Copyright: Aerospace Medical Association Aviation, Space, and Environmental Medicine x Vol. 79, No. 7 x July 2008 695 SHORT COMMUNICATION Seasonal Levels of Melatonin, Thyroid Hormones, Mood, and Cognition Near the Arctic Circle Tiina Pääkkönen, Juhani Leppäluoto, Tiina M. Mäkinen, Hannu Rintamäki, Aimo Ruokonen, Juhani Hassi, and Lawrence A. Palinkas P ÄÄKKÖNEN T, L EPPÄLUOTO J, M ÄKINEN TM, R INTAMÄKI H, R UOKONEN A, H ASSI J, P ALINKAS LA. Seasonal levels of melatonin, thyroid hormones, mood, and cognition near the Arctic Circle. Aviat Space Environ Med 2008; 79:695–9. Introduction: The associations between melatonin and thyroid hor- mones and changes in mood and cognitive performance caused by ex- posure to cold and darkness were examined in 12 circumpolar residents during winter and summer. Methods: Each participant was exposed to three different experimental conditions in random order: 1) 22°C and bright light; 2) 10°C and bright light; and 3) 10°C and dim light. The du- ration of each exposure was 24 h. Results: Increased serum melatonin and thyrotropin were associated with decreased rectal temperature (r 5 -0.446 – -0.580) and increased mean skin temperature (r 5 0.204– 0.519). Higher serum melatonin was associated with increased vigor (r 5 0.330) and decreased accuracy on simple cognitive tasks (r 5 -0.332 – -0.430). Increased serum free triiodothyronine (fT 3 ) was associated with decreased negative mood scores (r 5 -0.365 – -0.483), decreased response time (RT) on the simple reaction time (SRT) task (r 5 -0.606), and decreased accuracy on the addition/subtraction task (r 5 -0.372). Higher serum free thyroxine was associated with decreased fatigue and anger (r 5 -0.409 – -0.522). Increased serum thyrotropin was associ- ated with decreased accuracy and RT on the SRT task and decreased RT on the grammatical reasoning task (r 5 -0.315 – -0.415). Conclusions: Associations between serum melatonin and thyroid hormones with mood were consistent with the psychological changes associated with the polar triiodothyronine syndrome. Also, serum melatonin and thyro- tropin were associated with impaired and fT 3 with improved cognitive performance, supporting the decrements in cognitive performance asso- ciated with the polar triiodothyronine syndrome. Keywords: thyrotropin, triiodothyronine, thyroxine, mental performance, cognitive performance. C IRCUMPOLAR environments are characterized by remarkable seasonal changes in photoperiod and temperature, which have considerable effects on human mood and cognitive performance. Studies of polar expe- ditions and personnel in Antarctic research stations have reported increases in depressive symptoms and a decline in cognitive performance in clinically normal individuals during the winter months (15). Referred to as the “winter- over syndrome” (15), these symptoms exhibit some simi- larities to subsyndromal seasonal affective disorder (8). However, the mechanism by which light may affect mood and cognitive performance remains the subject of debate. Light intensity has been associated with suppression of melatonin (MLT). The MLT secretion appears to be con- siderably higher in winter than in summer in Arctic resi- dents (6). The MLT rhythm is a major transducer of pho- toperiod information for the timing of multiple diurnal and seasonal physiologic rhythms, including the rhythms of energetic arousal, mood, and cognitive performance. Reed and colleagues (12) have reported decreased to- tal triiodothyronine (tT 3 , 9%) and free triiodothyronine (fT 3 , 18%) concentrations accompanied by a 50% increase in integrated thyrotropin (TSH) response to thyrotropin-stimulating hormone administration during the austral winter in Antarctica. These alterations are also known to be associated with increased depressive symptomatology and disruption of cognitive perfor- mance in tasks involving short-term or working memory (13). Known as the polar triiodothyronine (T 3 ) syndrome, these alterations share many of the same characteristics with subclinical hypothyroidism. Circan- nual alteration of thyroid hormones has been observed to occur in Arctic (3) and Antarctic (13) residents. In a previous study, we documented that a short-time exposure to cold air and dim light was associated with a decline in response time on all cognitive tasks, an im- provement in accuracy on complex tasks, and a decline in accuracy on simple tasks in a group of healthy young residents living in an urban circumpolar setting (9). In this study, we assessed whether these changes were as- sociated with MLT levels and thyroid function. METHODS Subjects Study protocol was approved in advance by the ethics committee of the University of Oulu and Northern From the Department of Biomedicine/Physiology, (T. Pääkkönen, J. Leppäluoto, H. Rintamäki), Institute of Health Sciences, (T. M. Mäkinen, J. Hassi), and Institute of Diagnostics (A. Ruokonen), University of Oulu, Oulu, Finland; the Finnish Defence Forces, Centre for Military Medi- cine, Research and Development Unit, Lahti, Finland (T. M. Mäkinen); Physical work capacity, Finnish Institute of Occupational Health/Oulu, Oulu, Finland (H. Rintamäki); and School of Social Work, University of Southern California, Los Angeles, CA (L. A. Palinkas). This manuscript was received for review in June 2007. It was ac- cepted for publication in April 2008. Address reprint requests to: Tiina Pääkkönen, who is a tutor with the Finnish Institute of Occupational Health/Oulu, Aapistie 1, FIN- 90220 Oulu, Finland; tiina.paakkonen@oulu.fi Reprint & Copyright © by the Aerospace Medical Association, Alex- andria, VA. DOI: 10.3357/ASEM.2148.2008