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

Abstract

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.

Circadian genes, rhythms and the biology of mood disorders

“…In some studies, SAD sufferers have been found to have either a pronounced seasonal melatonin rhythm, or more daytime melatonin specifically in the winter, while healthy control subjects have no seasonal alterations in their melatonin rhythms (Danilenko et al, 1994;Wehr et al, 2001). However, other studies have found significant seasonal alterations in melatonin rhythms in healthy, nonaffected individuals, or even melatonin levels that are greater in the summer than the winter (Touitou et al, 1984;Kivela et al, 1988;Honma et al, 1992;Morera and Abreu, 2006). Much of this variability in melatonin measurements likely comes from the variations in seasonal differences between different areas of the world in which these studies were conducted.…”

Seasonal covariation of the circadian phases of rectal temperature and slow wave sleep onset

“…Most likely, then, this represents the net result of Most other studies in seasonal variation, both in support of photoperiodic entrainment after the stabilizing effect of (Illnerová et al 1985;Touitou et al 1986;Binkley et al 1990; secondary zeitgebers, as already described by Wehr and Usui et al 1995) and in contradiction with (Horne and Coyne colleagues (Wehr et al 1993(Wehr et al ). 1975Maruta et al 1987;Seon and Tokura 1989) the present…”

“…In this study, the 24 h rectal temperature curve and Published reports (Horne and Coyne 1975;Wirz-Justice et al the 24 h spectrum series of the EEG of six healthy subjects 1984; Illnerová et al 1985;Touitou et al 1986;Maruta et al have been recorded once every month for a whole year. 1987; Seon and Tokura 1989;Binkley et al 1990; Special attention was paid to the circadian phase of rectal al. 1992; Usui et al 1995;Wehr et al 1995;Emura et al 1996) temperature and the timing of slow wave sleep (SWS), because are diverse in methodology, varying from the use of sleep logs of the potential relevance of an abnormal internal phase in field research to extensive laboratory studies under more relationship for seasonal variations in mood (Czeisler et al or less well-controlled conditions.…”

Pharmaceutical Studies of Levothyroxine Sodium Hydrate Suppository Provided as a Hospital Preparation

“…The arm of the apparatus moved up and down automatically at a constant speed (40 rpm). One milliliter of the buffer was sampled at each time point (15,30,60,120,180, and 240 min), and 1 mL of fresh buffer was added to maintain the same volume. The sample was filtered through a syringe filter and analyzed by HPLC.…”

“…Rectal temperature in healthy men varies from 36 to 37.5°C over the course of a day (high in the daytime and low in the nighttime). 15) Thyroid hormones play an essential role in thermogenesis and hypothyroid patients tend to develop low body temperatures due to a reduction in thermogenesis. 16) We carried out the suppository release test at low temperatures (35°C, 36°C) to investigate the effect of temperature on the release of L-T 4 .…”