Circadian Levels of Serum Melatonin and Cortisol in relation to Changes in Mood, Sleep, and Neurocognitive Performance, Spanning a Year of Residence in Antarctica
Background. Altered circadian cortisol and melatonin rhythms in healthy subjects exposed to an extreme polar photoperiod results in changes in mood and sleep, which can influence cognitive performance. Materials and Methods. We assessed the circadian rhythm of 20 subjects who wintered over at Maitri ( S, E), India’s permanent Antarctic station, from November 2010 to December 2011. Serum cortisol and melatonin levels were measured by radioimmunoassay at 8？am, 3？pm, 8？pm, and 2？am in a single day, once each during the polar summer and winter photoperiods. Conventional psychological tests, Depression, Anxiety, and Stress Scale (DASS-42), Epworth Sleepiness Scale (ESS), and a computerized neurocognitive test battery were used to measure mood, sleep, and cognitive performance. Results. The mean scores for DASS42 were higher during midwinter suggesting the presence of “overwintering.” Mean diurnal cortisol levels during summer and winter were comparable, but the levels of melatonin were markedly higher during winter. Higher 8？am melatonin levels were associated with better sleep quality, lower depression scores, and better performance in tasks like attention, visual memory, and arithmetic. Conclusion. Timing of artificial light exposure and usage of melatonin supplements in improving sleep and cognitive performance in expedition teams are of future research interest. 1. Introduction Residence in Antarctica exposes humans working in the research bases to extremes of weather and photoperiod, in addition to geographic and social isolation. The annual average solar radiation decreases with increasing latitude, and this difference is marked during winter than in midsummer in the circumpolar regions. This alters temporal homeostasis and affects sleep wake cycles, mood, cognition and work performance of base personnel. The psychological disturbances in Antarctica, referred to as the “over winter syndrome,” may also relate to change in the circadian rhythms of the hormones cortisol and melatonin [1–3]. Photic stimuli are the primary synchronizer of the endogenous circadian pacemaker in the suprachiasmatic nucleus of the anterior hypothalamus. Therefore temporal modulation of the ambient light settings over a 24？hour period in Antarctica can promote better adjustment to the seasonal photoperiod. The endocrine control over the circadian pacemaker is reflected by the changes in serum levels of cortisol and the pineal indoleamine melatonin. Melatonin, noradrenaline, and acetylcholine decrease with light activation, whereas cortisol, serotonin, GABA, and dopamine levels
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