Biological Rhythms During Residence in Polar Regions

Abstract

At Arctic and Antarctic latitudes, personnel are deprived of natural sunlight in winter and have continuous daylight in summer: light of sufficient intensity and suitable spectral composition is the main factor that maintains the 24-h period of human circadian rhythms. Thus, the status of the circadian system is of interest. Moreover, the relatively controlled artificial light conditions in winter are conducive to experimentation with different types of light treatment. The hormone melatonin and/or its metabolite 6-sulfatoxymelatonin (aMT6s) provide probably the best index of circadian (and seasonal) timing. A frequent observation has been a delay of the circadian system in winter. A skeleton photoperiod (2 × 1-h, bright white light, morning and evening) can restore summer timing. A single 1-h pulse of light in the morning may be sufficient. A few people desynchronize from the 24-h day (free-run) and show their intrinsic circadian period, usually >24 h. With regard to general health in polar regions, intermittent reports describe abnormalities in various physiological processes from the point of view of daily and seasonal rhythms, but positive health outcomes are also published. True winter depression (SAD) appears to be rare, although subsyndromal SAD is reported. Probably of most concern are the numerous reports of sleep problems. These have prompted investigations of the underlying mechanisms and treatment interventions. A delay of the circadian system with “normal” working hours implies sleep is attempted at a suboptimal phase. Decrements in sleep efficiency, latency, duration, and quality are also seen in winter. Increasing the intensity of ambient light exposure throughout the day advanced circadian phase and was associated with benefits for sleep: blue-enriched light was slightly more effective than standard white light. Effects on performance remain to be fully investigated. At 75°S, base personnel adapt the circadian system to night work within a week, in contrast to temperate zones where complete adaptation rarely occurs. A similar situation occurs on high-latitude North Sea oil installations, especially when working 18:00–06:00 h. Lack of conflicting light exposure (and “social obligations”) is the probable explanation. Many have problems returning to day work, showing circadian desynchrony. Timed light treatment again has helped to restore normal phase/sleep in a small number of people. Postprandial response to meals is compromised during periods of desynchrony with evidence of insulin resistance and elevated triglycerides, risk factors for heart disease. Only small numbers of subjects have been studied intensively in polar regions; however, these observations suggest that suboptimal light conditions are deleterious to health. They apply equally to people living in temperate zones with insufficient light exposure. (Author correspondence: [email protected])

Keywords:

• Antarctic
• Arctic
• Circadian
• Light
• Melatonin
• Polar
• Sleep

ACKNOWLEDGMENTS

Studies by the author, referred to in this review, were supported throughout by the British Antarctic Survey, and in part by the Antarctic Funding Initiative, the Medical Research Council, the Institute of Petroleum, and The Energy Institute. Philips Lighting B.V. Eindhoven provided lighting equipment and an unrestricted research grant. Dr. Benita Middleton (Stockgrand Ltd., University of Surrey) supplied reagents, expertise, advice, and unlimited support. In addition to those mentioned by publication herein, the author wishes to thank all the Halley base doctors who have carried out chronobiology research projects at the ends of the Earth and all the willing (and unpaid) volunteers who took part in these studies. She would also like to thank Dr. Iain Grant, British Antarctic Survey Medical Unit, UK, Dr. Benita Middleton, University of Surrey, UK, and Michel Paul, Defense Research and Development, Canada, for their expert review of the manuscript.

Declaration of Interest: The author is a director and major shareholder of Stockgrand Ltd., which supplied reagents and expertise for Antarctic studies. This review was written during the tenure of a consultancy with the Canadian Ministry of Defense. The author reports no conflicts of interest. The author alone is responsible for the content and writing of the paper.