TY - JOUR

T1 - Summer-winter difference in 24-h melatonin rhythms in subjects on a 5-workdays schedule in Siberia without daylight saving time transitions

AU - Danilenko, Konstantin V.

AU - Kobelev, Eugenii

AU - Semenova, Ekaterina A.

AU - Aftanas, Lyubomir I.

N1 - Copyright © 2019 Elsevier Inc. All rights reserved.

PY - 2019/12/1

Y1 - 2019/12/1

N2 - The 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 ~6 a.m. and another at ~7 a.m. during their regular 5-workdays schedule. They collected 19 saliva samples at home over 24 h (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 h) 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, with a tendency for greater inter-individual phase variability. The phase delay was attributable to those subjects who got up at ~7 a.m. (and who were longer sleepers). The melatonin rhythm reflected well the sleep timing difference between the two groups in summer, whereas in winter this coherence was lost. In summary, timing of the circadian system is strictly synchronised in summer by the long light: short dark photoperiod (with sleep as a constituent of the 7 h 10 min dark phase of the cycle), whereas in winter, with the long dark nights (17 h 12 min), an inter-individual phase desynchrony and even abnormal melatonin patterns emerge, despite a constant sleep/social regimen, suggesting that the winter season is unfavourable for circadian status.

AB - The 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 ~6 a.m. and another at ~7 a.m. during their regular 5-workdays schedule. They collected 19 saliva samples at home over 24 h (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 h) 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, with a tendency for greater inter-individual phase variability. The phase delay was attributable to those subjects who got up at ~7 a.m. (and who were longer sleepers). The melatonin rhythm reflected well the sleep timing difference between the two groups in summer, whereas in winter this coherence was lost. In summary, timing of the circadian system is strictly synchronised in summer by the long light: short dark photoperiod (with sleep as a constituent of the 7 h 10 min dark phase of the cycle), whereas in winter, with the long dark nights (17 h 12 min), an inter-individual phase desynchrony and even abnormal melatonin patterns emerge, despite a constant sleep/social regimen, suggesting that the winter season is unfavourable for circadian status.

KW - Healthy individuals

KW - Melatonin rhythm

KW - No daylight saving time transitions

KW - Seasonality

KW - Stable social/sleep regimen

KW - SLEEP

KW - LIGHT

KW - SENSITIVITY

KW - EXCRETION

KW - HUMAN CIRCADIAN PACEMAKER

KW - PLASMA MELATONIN

KW - PHOTOPERIOD

KW - ENTRAINMENT

KW - EXPOSURE

KW - CORTISOL

UR - http://www.scopus.com/inward/record.url?scp=85074224524&partnerID=8YFLogxK

U2 - 10.1016/j.physbeh.2019.112686

DO - 10.1016/j.physbeh.2019.112686

M3 - Article

C2 - 31626888

AN - SCOPUS:85074224524

VL - 212

JO - Physiology and Behavior

JF - Physiology and Behavior

SN - 0031-9384

M1 - 112686

ER -