Summer-winter difference in 24-h melatonin rhythms in subjects on a 5-workdays schedule in Siberia without daylight saving time transitions

Publication date: Available online 15 October 2019Source: Physiology & BehaviorAuthor(s): Konstantin V. Danilenko, Eugenii Kobelev, Ekaterina A. Semenova, Lyubomir I. AftanasABSTRACTThe study aimed to quantify a seasonal change in circadian rhythms and its relationship to the social/sleep regimen in humans living in Novosibirsk (55°N), using the naturalistic situation that daylight saving time transitions have been abolished in Russia. Sixty-three volunteers entered the study, and 46 completed it. One group got up at ∼6am and another at ∼7am during their regular 5-workdays schedule. They collected 19 saliva samples at home over 24 hours (including 2 samples during the night) on July 3-4, and December 18-19, 2015. Salivary melatonin was measured using radioimmunoassay; the times of evening onset and morning offset were objectively determined using the hockey-stick algorithm and served as circadian phase markers. Nearly all melatonin profiles were normal in summer (high nighttime and low daytime levels), whereas in winter, significantly more – 8 profiles – were abnormal (additional daytime peak, out-of-phase daytime secretion, or absence of secretion), of which 3 (plus 1 for other reasons) could not be included in the further analysis. The duration of melatonin secretion (somewhat less than 12 hours) and amount of melatonin secreted did not differ between seasons. In winter compared to summer the melatonin rhythm, on average, significantly phase delayed by half-an-hour...
Source: Physiology and Behavior - Category: Physiology Source Type: research