by Josephine Arendt
Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
Josephine Arendt PhD is a pioneer and international leader of circadian research in many domains: she developed the first radioimmunoassay for the pineal hormone melatonin, and first recognized and used the potential of polar regions to find out what daylight — or lack of — does to humans.
Polar regions are hostile environments for human beings. We are not equipped like the wildlife to survive the extreme temperatures and light conditions without extensive use of specialized clothing, housing, heating, lighting, machinery and communications. The first great maritime explorers did not stay long and the vast continent of Antarctica is still mostly unexplored (Scott, 1912, “Great God this is an awful place“). For the moment, a signed treaty conserves the continent for peace and science, and its main temporary inhabitants are scientists and technicians, mostly concerned with the physical environment (a focus is climate change) and biology, with support staff.
In winter, due to the extensive Antarctic ice sheet, bases may be isolated and inaccessible for several months, and with no natural sunlight. For example at 75 °S the sun does not rise for 3 months in the winter, and does not set for 3 months in the summer. The isolation has been compared to living in space, and bases may be used as as analogues for the space environment. For a scientist, the personnel themselves provide a wonderful source of healthy experimental volunteers living together in the same conditions for extensive periods, often for more than a year. There is much information on the psychology of Antarctic base personnel, but here I will consider the light environment since it is a critical feature of the Antarctic experience.
Light-dark conditions are the most important factor governing our ability to keep our circadian rhythms of physiology (such as hormones) and behavior (such as sleep) stay properly synchronized to a 24-hour day. This synchrony is very important to physical and mental health, and Antarctic conditions allow us to investigate human responses to different light environments, especially in winter. These include the influence of daylength, light intensity, light sensitivity, the effects of different spectral qualities of light, and the use of timed light exposure to optimize rhythms. The availability of modern equipment for the continuous monitoring of light exposure, activity and rest (sleep), together with modern satellite communications, has made a great difference to the scope of Antarctic research.
In winter, when the sun does not rise for weeks/months (“sundown”) and outdoor activity is minimal, the lighting source is artificial and can be manipulated. An Antarctic study provided some of the first evidence for the importance of light to our circadian physiology. In the dim light of winter, the melatonin circadian rhythm was seen to delay to later times of day. Extra bright white light pulses to mimic a spring daylength were able to restore the appropriate and stable timing.
Summer, when the sun does not set for weeks/months, is very different with larger numbers of base personnel and visitors, heavy outdoor work, and the requirement to wear efficient UV blocking sunglasses when outdoors. The use of these glasses means that the actual light exposure at eye level is hard to know. We know that people like to go skiing in the middle of the night and such behavior does not help any controlled light study!
Sleep complaints are common in polar regions both in the summer, with 24 hours of daylight, and in the winter, with 24 hours of darkness. Sleep is critically important for human beings to function well. The quality and quantity of sleep that we get depends to a large extent on what time we sleep during our “biological night.” Biological night is when our internal clock is in night mode with low body temperature and high levels of the hormone melatonin. If we sleep during night mode we usually sleep well, but during day mode sleep is shorter and of less quality. Body rhythms are shifted (delayed, as shown by the melatonin rhythm) when there is insufficient bright light in the morning in winter to reset the internal clock. If we try to sleep at the conventional time it will be too early for good sleep. In summer, bright light (especially blue light) present in the evening will also delay the internal clock but is easily avoided.
The delays in getting to sleep and waking up in the polar winter can be countered by provision of extra white light during the whole day and blue-enriched light may be more effective than white light. Extra morning light by itself may also be sufficient. Summer delays can obviously be addressed by avoiding bright light in the evening and any light at night.
Antarctica also lends itself to shift work studies in different light conditions, with both night work and day work in the same environment, with no necessity to travel home. Unusually, here, most people adapt their circadian rhythms to night work in winter. The possibility of obtaining blood samples when adapted and non-adapted to night work in Antarctica has led to some important observations regarding the timing of meals and metabolic risk factors for cardiovascular disease.
The main disadvantage of Antarctica for research is the small number of subjects on most bases. Combining data from different bases is one approach but far from ideal. Using subjects as their own controls is another possibility together with collecting several years worth of data. Nothing is simple, and as ever there is more research needed to determine optimum lighting conditions for Antarctic residence. However the new base of Halley 6 has recognized the importance of light to health, and has used circadian principles in its lighting design. Unfortunately, it is currently closed over winter.