Absence of Seasonal Variation in the Phase of the Endogenous Circadian Rhythm in Humans

Humans may be subject to seasonal variations, as evidenced by the existence of seasonal affective disorder (SAD) and midwinter insomnia. However, some recent studies have shown that the seasonal variation in the phase of the circadian rhythm is relatively weak in healthy humans. In the present study...

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Bibliographic Details
Published in:Chronobiology international 1998-01, Vol.15 (6), p.623-632
Main Authors: Van Dongen, Hans P. A., Kerkhof, Gerard A., Souverijn, John H. M.
Format: Article
Language:English
Subjects:
Adolescent
Biological and medical sciences
Biological Clocks
Body Temperature
Chronobiology
Circadian Rhythm - physiology
Constant routine
Darkness
Endogenous circadian phase
Fundamental and applied biological sciences. Psychology
Human
Humans
Hydrocortisone - secretion
Hydrocortisone - urine
Light
Male
Netherlands
Photoperiod
Reference Values
Seasonal Affective Disorder - etiology
Seasonal variation
Seasons
Sleep Initiation and Maintenance Disorders - etiology
Vertebrates: anatomy and physiology, studies on body, several organs or systems
Zeitgebers
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Summary:Humans may be subject to seasonal variations, as evidenced by the existence of seasonal affective disorder (SAD) and midwinter insomnia. However, some recent studies have shown that the seasonal variation in the phase of the circadian rhythm is relatively weak in healthy humans. In the present study, evidence is found that there is no seasonal variation in the phase of the endogenous circadian rhythm at all. Body temperature, cortisol excretion, and subjective alertness of six subjects recorded under constant routine conditions showed no systematic seasonal variation in circadian phases. This finding indicates that secondary zeitgebers blocked or counterbalanced the seasonal variation in the entrainment effect of the natural photo-period. The human being may live in an environment in which the photoperiod has lost its status of primary zeitgeber. (Chronobiology International, 15(6), 623-632, 1998)
ISSN:0742-0528
1525-6073
DOI:10.3109/07420529808993198