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Nighttime Drop in Body Temperature: A Physiological Trigger for Sleep Onset?
Abstract and Figures
Relationships between changes in the slope of the body temperature (BT) and the initiation of sleep were examined in 44 subjects ranging from 19 to 82 years of age. Following an adaptation night, subjects remained in the laboratory for a baseline night and 72 hours in temporal and social isolation, with strictly limited behavioral options ("disentrainment") during which continuous electroencephalograph (EEG) and BT were recorded. Polysomnographic sleep variables (e.g. sleep onset, percentage of each sleep stage) were determined for nighttime sleep periods at baseline and during the disentrainment period. Periods of the BT curve surrounding these sleep bouts were examined for minute to minute changes, and the time at which the maximum rate of decline (MROD) in temperature occurred was compared with the time of sleep onset (SO) and sleep quality parameters. On the baseline night, the MROD occurred, on average, 60 minutes prior to SO. During disentrainment, the MROD occurred, on average, 44 minutes prior to SO. The proximity of MROD to SO did not affect subsequent sleep quality on the baseline night, but during disentrainment, there were significant correlations between the interval from MROD to sleep onset and the amount of slow-wave sleep (SWS) obtained during the sleep bout. There were no significant age differences on variables related to MROD on baseline night, but the timing of both MROD and SO were significantly advanced in older, relative to younger, subjects during the disentrainment period. It is suggested that a rapid decline in core body temperature increases the likelihood of sleep initiation and may facilitate an entry into the deeper stages of sleep.
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... The relationship between temperature and sleep has been usually explained by the circadian cycle of sleep. For sleep initiation and progression into deeper sleep stages, it is necessary for the core body temperature to rapidly decrease (Murphy and Campbell 1997;Kräuchi and Wirz-Justice 2001). Extreme ambient temperatures can disrupt the decrease in core body temperature, leading to insomnia (Lack et al. 2017). ...
Insomnia is a growing health concern globally, with significant implications for public health. Most studies have primarily focused on the effects of nighttime temperatures on sleep problems. However, there is a lack of studies comparing nighttime temperatures with daytime temperatures, which are more closely related to daily life activities. This study aimed to explore a short–term association of nighttime and daytime ambient temperature with emergency department (ED) visits for insomnia in the capital city of South Korea. A time–stratified case–crossover design was employed using a conditional logistic regression model. A distributed lag non–linear model was utilized to explore potential non–linear and lag effects of ambient temperature on ED visits for insomnia. Odds ratio (OR) for temperature with maximum ED visits for insomnia (MaxIT) and that for temperature with minimum ED visits for insomnia (MinIT) were calculated and compared. We observed significant associations at high temperatures for both nighttime and daytime (nighttime: 25.0℃ (94.1%) [OR: 1.82, 95% CIs: 1.31–2.55], daytime: 30.6℃ (99.0%) [OR: 2.13, 95% CIs: 1.49–3.06]) compared to MinIT (-8.5℃ (2.7%) and − 8.4℃ (1.0%), respectively). Subgroup analyses found significant associations at high temperatures in females, individuals aged 35–49, and those without comorbidities, and during spring, fall, and winter, for both daytime and nighttime. Our findings provide insights for proactive public health strategies for managing insomnia during global temperature rise.
... (1) proper secretion of melatonin: exercise causes serotonin secretion and promotes melatonin secretion (Aoyama & Shibata, 2017;Kruk et al., 2021); (2) mitochondrial activation: mitochondrial biosynthesis and antioxidant capacity increase, promoting adaptive responses in the body (Hartmann & Kempf, 2023); (3) activation of brain-derived neurotrophic factor (BDNF): in rodents, BDNF is activated, and BDNF activation increases slow wave sleep and deepens sleep (Tan et al., 2020); and (4) lower core body temperature: an increase in body temperature due to exercise causes peripheral blood vessels to dilate, which lowers core body temperature and promotes sleep onset (Gilbert et al., 2004;Murphy & Campbell, 1997). The most important aspect of this study is that it is the first to report from the sleep stage that increased steps may improve sleep quality during the winter months. ...
Objective: We aimed to assess seasonal and age-related variations in sleep quality using Fitbit data and offer lifestyle recommendations for enhancing winter sleep quality. Methods: Fitbit sleep and activity data of 51 participants randomly recruited from members of the Association for Research in Supporting System of Chronic Disease, a nonprofit organization in the Yamanashi Prefecture of Japan, were collected and retrospectively analyzed from July to December 2022. Sleep stage targets were set at 10% to 25% for deep sleep, 50% to 60% for shallow sleep, and 20% to 25% for REM sleep. Participants were categorized into improved, unchanged, and worsened groups based on sleep stage unit changes between August and December. Results: The median (interquartile range) age was 71 (68–74) years old. There were eight participants in the improved group, 23 in the unchanged group, and nine in the worsened group. The improved group showed significantly more steps (990 ± 1,102 steps/day, p = .039) in December than in August, while the worsened group showed fewer steps (−507 ± 1,638 steps/day, p = .38). Conclusion: Increasing step count in winter may improve sleep quality, as assessed by sleep stage. Further research considering potential confounders and factors affecting winter sleep is needed to support and extend these findings.
... The observed colder thermal preference before sleep aligns with previous research, indicating that individuals tend to prefer cooler temperatures before sleeping (Uno et al., 2018). However, as the body's metabolic rate decreases during sleep, the preference for higher temperatures slightly increases, resulting in the shift of mean TP to a higher value (Murphy & Campbell, 1997;Pan et al., 2012b). Regarding air movement sensation, participants reported a moderate level of sensation both before sleep and after waking up. ...
... This reduction in SL is likely attributed to the fact that the training sessions in this study were conducted in the afternoon (2 p.m.), as it is known that physical exercise performed in the late afternoon can lead to shorter latencies for the onset of sleep (Youngstedt, 2005). This can be explained, from a physiological point of view, by the thermoregulatory hypothesis, which is based on the evidence that the onset of sleep is triggered by the reduction in body temperature that occurs circadianly at the beginning of the night (Murphy & Campbell, 1997). Furthermore, it is important to mention that the hypothalamus has a primary role in regulating body temperature and inducing sleep (Lu et al., 2000). ...
Purpose: The aim of this study was to examine how intensifying training loads over a week affects the sleep patterns of young soccer players on the nights immediately following the intensified training sessions. Methods: Quasi-experimental study. Fifteen young athletes participants of a team engaged in national level competition, underwent two weeks of training with varying load magnitudes—Week 1: low accumulated training load and Week 2: intensified training loads [40% increase in external training load(ETL)]. To characterize the intensification of the workload, the methods PlayerLoad and RPE-Session were employed to measure ETL and internal training load(ITL), respectively. Total sleep time(TST), total time in bed(TTB), sleep efficiency(SE), sleep latency(SL), and wake after sleep onset(WASO) were obtained using actigraphy and daily sleep log. The variables were compared among the days of week (e.g. Monday of week 1 with Monday of week 2, and so forth). Results: Acute training intensification in week 2 led to significant increases in ETL and ITL on Monday and on Wednesday(p < .05), and ETL(p < .05) on Friday on the second week. Improvements in sleep were observed (Tuesday—TST:+80 min, WASO:-29.3 min, SL:-8 min, SE:+9%; Thursday—TST:+86 min, SL:-4 min, SE:+4%; Saturday—TST:+40 min, SL:+1 min) compared to the same day of the previous week. Correlations between ETL and ITL(r = 0.637), ITL and TST(r = 0.572), ITL and SE(r = 0.548) were found. Conclusion: Intensification of training loads results in alterations in sleep variables, notably an elevated TST and SE in the days subsequent to the acute load increment.
Insomnia is a growing health concern globally, which can obstruct daytime functionality, reduce overall quality of life, and result in various diseases including depression, anxiety disorders and cardiovascular diseases. Increasing literature have focused on the potential role of ambient temperature in sleep problems, but the association remains inconclusive. This study aimed to explore a short-term association of ambient temperature with emergency department (ED) visits for insomnia in the capital city of South Korea. Using the National Emergency Department Information System database from 2008 to 2017, 7,855 patients who visited ED for insomnia (International Classification of Disease, 10th revision code F51.0 and G47.0) were identified. A time-stratified case-crossover design was employed using a conditional logistic regression model. A distributed lag non-linear model was utilized to explore potential non-linear and lag effects of ambient temperature on ED visits for insomnia. Odds ratio (OR) for temperature with maximum ED visits for insomnia (MaxIT) and that for temperature with minimum ED visits for insomnia (MinIT) were calculated and compared. A significant association was found between ambient temperature and ED visits for insomnia. Total insomnia increased significantly at a high temperature (MaxIT: 29.3℃, OR: 2.09 [95% CIs: 1.43–3.04]) compared to that at a MinIT (-8.9℃). Furthermore, the association between high temperature and insomnia was found to be stronger in females, 35–49 age group, and patients without comorbidities. The risk of insomnia is significantly increased in high ambient temperature. Our findings provide insights for proactive public health strategies for managing insomnia during global temperature rise.
Individuals experience difficulty falling asleep in a new environment, termed the first night effect (FNE). However, the impact of the FNE on sleep-induced brain plasticity remains unclear. Here, using a within-subject design, we found that the FNE significantly reduces visual plasticity during sleep in young adults. Sleep-onset latency (SOL), an indicator of the FNE, was significantly longer during the first sleep session than the second session, confirming the FNE. We assessed performance gains in visual perceptual learning after sleep and increases in the excitatory-to-inhibitory neurotransmitter (E/I) ratio in early visual areas during sleep using magnetic resonance spectroscopy and polysomnography. These parameters were significantly smaller in sleep with the FNE than in sleep without the FNE; however, these parameters were not correlated with SOL. These results suggest that while the neural mechanisms of the FNE and brain plasticity are independent, sleep disturbances temporarily block the neurochemical process fundamental for brain plasticity.
Energy expenditure is lower during sleep than relaxed wakefulness. However, there is disagreement as to the particular metabolic changes that produce the difference. The present study assessed the contribution of sleep, circadian cycle, and the specific dynamic action effect of the evening meal to the sleep period fall in metabolic rate. Five subjects were tested for a total of nine nights under three conditions in a repeated-measures design. Subjects were confined to bed throughout their usual sleep period but were instructed to go to sleep 0, 3, or 6 h after their usual time for lights out. O2 consumption was measured in all conditions for the 0.5 h before and after each of the times for lights out and then throughout the sleep period after lights out. The results demonstrated that changes in energy expenditure during the sleep period are a function of both sleep and circadian cycle. In this study, the contribution of the two components was approximately equal. However, the effect of sleep was rapid asymptoting within 15 min of sleep onset, whereas that of circadian cycle was constant over the assessment period.
In the realm of human circadian rhythms, the masking effect is defined as the change in the course of deep body temperature induced by changes in the degree of physical activity, or by the alteration between sleep and wake. This effect is particularly obvious during internal desynchronization where the rhythms of deep body temperature, and the sleep-wake sleep-wake sleep cycle — i.e. one of the masking factors — run with different periods. Every sleep onset is accompanied by a rapid drop, and wake onset by a rapid rise in deep body temperature, each one with an overshoot of about 50% of the steady state variations. When rhythms are calculated, with the dominant temperature period as the screening period, exclusively from data obtained during sleep episodes, on the one hand, and from those obtained exclusively during wake, on the other, two average cycles emerge: the ‘sleep temperature curve’ and the ‘wake temperature curve’. Both run in parallel but are separated by the ‘masking effcct’. As derived from many experiments, the mean masking effect amounts to 0.28±0.06°C. The masking effect also depends to some extent on the phase of the temperature rhtthm; it is larger than average around the temperature maximum and during the descending phase of the temperature cycle, where the alertness commonly is highest and the probability to sleep, in general, and the REM sleep propensity, in particular, are smaller than average. This also can be interpreted to indicate that the sleep temperature curve is phase advanced relative to the wake temperature curve; this, on the average, by 0.9±0.3 h.
Patterns of sleep and wakefulness exhibited in an environment without time cues are generally considered to be monophasic, with a distinct relationship between sleep episodes and the minimum of body core temperature. In some cases this relationship between major sleep episodes and temperature becomes replaced by an apparently varying phase relationship between the two variables called "spontaneous internal desynchronization". In the present study the sleep-wake and temperature data of six subjects living in an environment without time cues and exhibiting internal desynchronization were reanalyzed to include subjectively designated naps. Two groups of naps were identified based on their phase positions relative to temperature, with one group occurring around the temperature minimum and another group clustering approximately halfway between successive minima. The results support the suggestion that neither monophasic sleep placement nor sleep patterns typically associated with spontaneous internal desynchronization reflect biological sleep tendency. Rather, sleep tendency is reflected more accurately by the bimodal sleep patterns exhibited by subjects who are allowed to time their sleep and waking with no restrictions.
Six healthy male subjects were exposed to seven different bedtime conditions, one per week. Bedtimes were scheduled in 4-h intervals, resulting in times without sleep ranging from 16 h to 40 h. The influences of overt zeitgebers were minimized and the subjects were allowed to sleep until they felt they had slept enough. Rectal temperature was measured continuously and showed a circadian rhythm during both sleeping and waking. A fall in temperature immediately after sleep onset was noted at all bedtimes except at 0700 and 1900 h. In the majority of cases temperature rose toward the end of sleep, i.e., awakenings tended to occur during the rising phase of the circadian temperature rhythm. It was suggested that the phase of the body temperature rhythm is an important factor in determining sleep duration, mainly through terminating sleep during the high or rising parts of the rhythm.
The sleep-wake cycle and the circadian rhythm of rectal temperature were recorded in subjects who lived singly in an isolation unit. In 10 subjects, the freerunning rhythms remained internally synchronized, 10 other subjects showed internal desynchronization. Times of onset and end of bedrest ("sleep") were determined in each cycle and referred to the phase of the temperature rhythm. In the synchronized subjects, onset of sleep occurred, on the average, 1.34 h before the minimum of temperature, and end of sleep 6.94 h thereafter, with narrow distributions. The desynchronized subjects had a broad bimodal distribution of sleep onsets (peaks 6.3 and 1.3 h before the minimum); the duration of sleep varied between more than 15 h when sleep began about 10 h before the temperature minimum, and less than 4 h when sleep began several hours after the minimum. The dependence of sleep duration on body temperature is interpreted as a continuing action of the coupling forces between the two rhythms after mutual synchronization is lost.