Sleep deficits in the High Arctic summer in relation to light exposure and behaviour: use of melatonin as a countermeasure.
BACKGROUND
There are conflicting reports regarding seasonal sleep difficulties in polar regions. Herein we report differences in actigraphic sleep measures between two summer trials (collected at Canadian Forces Station Alert, 82.5°N, in 2012 and 2014) and evaluate exogenous melatonin for preventing/treating circadian phase delay due to nocturnal light exposure.


METHODS
Subjects wore actigraphs continuously to obtain sleep data. Following seven days of actigraphic recording the subjects filled out questionnaires regarding sleep difficulty and psychosocial parameters and subsequently remained in dim light conditions for 24 hours, during which saliva was collected bihourly to measure melatonin. During Trial 2, individuals who reported difficulty sleeping were prescribed melatonin, and a second saliva collection was conducted to evaluate the effect of melatonin on the circadian system.


RESULTS
Trial 1 subjects collectively had late dim light melatonin onsets and difficulty sleeping; however, the Trial 2 subjects had normally timed melatonin rhythms, and obtained a good quantity of high-quality sleep. Nocturnal light exposure was significantly different between the trials, with Trial 1 subjects exposed to significantly more light between 2200 and 0200h. Melatonin treatment during Trial 2 led to an improvement in the subjective sleep difficulty between the pre- and post-treatment surveys; however there were no significant differences in the objective measures of sleep.


CONCLUSIONS
The difference in sleep and melatonin rhythms between research participants in June 2012 and June 2014 is attributed to the higher levels of nocturnal light exposure in 2012. The avoidance of nocturnal light is likely to improve sleep during the Arctic summer.
Defence Research and Development Canada, Toronto, ON, Canada M3K2C9.
Michel A
MA
Paul
Defence Research and Development Canada, Toronto, ON, Canada M3K2C9. Electronic address: ryan.love@drdc-rddc.gc.ca.
Ryan J
RJ
Love
Defence Research and Development Canada, Toronto, ON, Canada M3K2C9.
Andrea
A
Hawton
Canadian Forces Health Services Centre (Atlantic), Halifax, NS, Canada B3K 5X5; Canadian Forces Station - Alert, Nunavut, Canada.
Kaighley
K
Brett
Defence Research and Development Canada, Toronto, ON, Canada M3K2C9.
Donald R
DR
McCreary
University of Surrey, Guildford, Surrey GU2 7XH, UK.
Josephine
J
Arendt
D056044:Actigraphy; D000328:Adult; D001110:Arctic Regions; D002170:Canada; D002492:Central Nervous System Depressants / Q000627:therapeutic use*; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D008297:Male; D008550:Melatonin / Q000378:metabolism / Q000627:therapeutic use*; D008875:Middle Aged; D012621:Seasons; D020178:Sleep Disorders, Circadian Rhythm / Q000175:diagnosis / Q000209:etiology / Q000517:prevention & control*; D013472:Sunlight; D013997:Time Factors; D055815:Young Adult
D002492:Central Nervous System Depressants; D008550:Melatonin
Circadian rhythms; Dim light melatonin onset; Fatigue; Polar regions