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Am J Physiol Regul Integr Comp Physiol 262: R885-R891, 1992;
0363-6119/92 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 5 885-R891, Copyright © 1992 by American Physiological Society

ARTICLES

Seasonal variation in the human circadian rhythm: dissociation between sleep and temperature rhythm

K. Honma, S. Honma, M. Kohsaka and N. Fukuda
Department of Physiology, Hokkaido University School of Medicine, Sapporo, Japan.

The circadian rhythms of sleep-wakefulness, rectal temperature, and plasma melatonin were measured in 10 healthy male subjects for five consecutive seasons. To minimize direct effects of seasonally changing environmental factors, the subjects stayed in a living facility for 4 days in each season, where ambient temperature, humidity, and social contacts were controlled, while the light intensity of the living room was substantially influenced by natural daylight. Seasonal variations were found in the timing of sleep, the mean body temperature, the phases of circadian temperature and melatonin rhythms, and the phase relation between sleep and the rectal temperature rhythm. The subjects went to bed earliest in summer, intermediate in spring and autumn, and latest in winter. A similar but more pronounced seasonality was observed in the wake-up time, which was earlier in summer than in winter. The acrophases of the rectal temperature and plasma melatonin rhythms, which were calculated by fitting a cosine curve, were located in an earlier time of day in summer than in winter. The phase-angle difference of the rectal temperature rhythm to sleep varied seasonally and was more positive in summer than in winter. These findings indicate that not only the external (to the local time) but also the internal (between circadian rhythms) phase relations of the human circadian rhythms depend on season.


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S. Yoneyama, S. Hashimoto, and K. Honma
Seasonal changes of human circadian rhythms in Antarctica
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1999; 277(4): R1091 - R1097.
[Abstract] [Full Text] [PDF]


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