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.

Circadian Variation of Melatonin, Light Exposure, and Diurnal Preference in Day and Night Shift Workers of Both Sexes

“…Individual circadian phase assessed by melatonin timing (21,25) and chronotype has been associated with workers' adaptability to shift-work schedules (24). Evening types report better tolerance for night work and quicker adaptation (shift of the circadian rhythms) than morning types (20). We did not find an association between diurnal preference and aMT6s acrophase in night shift workers, as we had expected, perhaps because we lacked subjects with extreme morning or evening preferences, or due to low numbers.…”

“…To date, only a few of these studies have been able to address this issue using objective light exposure measurements (12,15,16,18,19). Furthermore, after several nights worked, some night shift workers can adapt to their shift schedule and melatonin peak time shifts to coincide with the daytime sleep episode (20)(21)(22). In most studies, only absolute aMT6s levels were assessed and not peak time of production.…”

Mars 520-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing

“…2) indicate that these problems occurred early in the mission and persisted unabated. Such individual differences in disturbances of sleep-wake regulation are similar to those identified in winter-over polar expeditions (15,26), which are often considered analogs for the study of behavioral reactions to the prolonged isolation of spaceflight (27)(28)(29)(30). The fact that sleep-wake disruptions occur during confinement and isolation in some individuals more than others is consistent with increasing evidence that there are phenotypic and genotypic differences in vulnerability to both alterations of sleep and the resulting neurobehavioral consequences (31)(32)(33)(34)(35)(36)(37).…”

The aging clock: circadian rhythms and later life

“…Circadian rhythms provide an adaptive mechanism for organisms to coordinate cellular processes, physiological functions, and behaviors with the predictable 24-hour cycle of light and dark on Earth (10). In mammals, the suprachiasmatic nucleus (SCN) is the master circadian clock.…”