Sleep during an Antarctic summer expedition: new light on "polar insomnia".

Sleep complaints are consistently cited as the most prominent health and well-being problem in Arctic and Antarctic expeditions, without clear evidence to identify the causal mechanisms. The present investigation aimed at studying sleep and determining circadian regulation and mood during a 4 months Antarctic summer expedition. All data collection was performed during the continuous illumination of the Antarctic summer. After an habituation night and acclimatization to the environment (3 weeks), ambulatory polysomnography (PSG) was performed in 21 healthy male subjects, free of medication. 18 hours profile (saliva sampling every 2 hr) of cortisol and melatonin were assessed. Mood, sleepiness and subjective sleep quality were assessed and the psychomotor vigilance task was administered. PSG showed, in addition to high sleep fragmentation, a major decrease in slow wave sleep (SWS) and an increase in stage R sleep. Furthermore, the ultradian rhythmicity of sleep was altered, with SWS occurring mainly at the end of the night and stage R sleep at the beginning. Cortisol secretion profiles were normal; melatonin secretion however showed a severe phase delay. There were no mood alterations according to the POMS scores, but the PVT showed an impaired vigilance performance. These results confirm previous reports on "polar insomnia" -the decrease in SWS- and present novel insight -the disturbed ultradian sleep structure. A hypothesis is formulated linking the prolonged SWS latency to the phase delay in melatonin.

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