Chronic high-caloric diet accentuates age-induced sleep alterations in mice

The interplay between macronutrients and sleep: focus on circadian and homeostatic processes

Sleep disturbances are an emerging risk factor for metabolic diseases, for which the burden is particularly worrying worldwide. The importance of sleep for metabolic health is being increasingly recognized, and not only the amount of sleep plays an important role, but also its quality. In this review, we studied the evidence in the literature on macronutrients and their influence on sleep, focusing on the mechanisms that may lay behind this interaction. In particular, we focused on the effects of macronutrients on circadian and homeostatic processes of sleep in preclinical models, and reviewed the evidence of clinical studies in humans. Given the importance of sleep for health, and the role of circadian biology in healthy sleep, it is important to understand how macronutrients regulate circadian clocks and sleep homeostasis.

Long-Term Effect of a Single Dose of Caffeine on Sleep, the Sleep EEG and Neuronal Activity in the Peduncular Part of the Lateral Hypothalamus under Constant Dark Conditions

Background: Caffeine is a central nervous system stimulant that influences both the sleep–wake cycle and the circadian clock and is known to influence neuronal activity in the lateral hypothalamus, an important area involved in sleep–wake regulation. Light is a strong zeitgeber and it is known to interact with the effect of caffeine on the sleep–wake cycle. We therefore wanted to investigate the long-term effects of a single dose of caffeine under constant dark conditions. Methods: We performed long-term (2 days) electroencephalogram (EEG)/electromyogram recordings combined with multi-unit neuronal activity recordings in the peduncular part of the lateral hypothalamus (PLH) under constant darkness in Brown Norway rats, and investigated the effect of a single caffeine treatment (15 mg/kg) or saline control given 1 h after the onset of the endogenous rest phase. Results: After a reduction in sleep and an increase in waking and activity in the first hours after administration, also on the second recording day after caffeine administration, rapid eye movement (REM) sleep was still reduced. Analysis of the EEG showed that power density in the theta range during waking and REM sleep was increased for at least two days. Neuronal activity in PLH was also increased for two days after the treatment, particularly during non-rapid eye movement sleep. Conclusion: Surprisingly, the data reveal long-term effects of a single dose of caffeine on vigilance states, EEG, and neuronal activity in the PLH. The absence of a light–dark cycle may have enabled the expression of these long-term changes. It therefore may be that caffeine, or its metabolites, have a stronger and longer lasting influence, particularly on the expression of REM sleep, than acknowledged until now.

Changes in sleep EEG with aging in humans and rodents

Sleep is one of the most ubiquitous but also complex animal behaviors. It is regulated at the global, systems level scale by circadian and homeostatic processes. Across the 24-h day, distribution of sleep/wake activity differs between species, with global sleep states characterized by defined patterns of brain electric activity and electromyography. Sleep patterns have been most intensely investigated in mammalian species. The present review begins with a brief overview on current understandings on the regulation of sleep, and its interaction with aging. An overview on age-related variations in the sleep states and associated electrophysiology and oscillatory events in humans as well as in the most common laboratory rodents follows. We present findings observed in different studies and meta-analyses, indicating links to putative physiological changes in the aged brain. Concepts requiring a more integrative view on the role of circadian and homeostatic sleep regulatory mechanisms to explain aging in sleep are emerging.

The association between sleep duration, bedtimes, and early pubertal timing among Chinese adolescents: a cross-sectional study

BACKGROUND AND OBJECTIVE

Early pubertal timing is associated with sleep among Western adolescents, but little is known about this association in Chinese adolescents, especially with regard to the association between bedtimes and early pubertal timing. This paper aimed to identify the association between sleep duration, bedtimes, and early pubertal timing in Chinese adolescents.

METHODS

An anonymous cross-sectional survey was conducted among primary and junior middle students (grades 3 to 9) from QiJiang District, ChongQing, China. Participants were recruited by applying stratified cluster sampling. Pubertal timing, sleep duration, and bedtimes were assessed using the Pubertal Development Scale and a self-designed sleep questionnaire. We utilized multivariable logistic linear regression (MLLR) to test the association between sleep duration, bedtimes, and pubertal timing.

RESULTS

A total of 5461 adolescents were evaluated, with mean age and BMI values of 11.41 ± 2.05 and 18.03 ± 3.03, respectively, of whom 1257 (23.02%) were in early pubertal timing. In MLLR controlling for age, BMI, family economic status, and other covariates, sufficient sleep (b = - 0.214, P = 0.032, OR = 0.808, 95% CI 0.664-0.982) was negatively related to early pubertal timing, and later bedtime (b = 0.195, P < 0.001, OR = 1.215, 95% CI 1.104-1.338) was positively associated with early pubertal timing.

CONCLUSION

Students with early pubertal timing had less sleep duration and later bedtimes, which may be the result of increased stress caused by physical and psychological changes. Therefore, more attention should be paid to pubertal health education for adolescents during puberty. Further longitudinal studies are needed to confirm the causality between sleep and early pubertal timing in Chinese adolescents.

Sleep and ageing: from human studies to rodent models

Sleep duration and lifespan vary greatly across Animalia. Human studies have demonstrated that ageing reduces the ability to obtain deep restorative sleep, and this may play a causative role in the development of age-related neurodegenerative disorders. Animal models are widely used in sleep and ageing studies. Importantly, in contrast to human studies, evidence from laboratory rodents suggests that sleep duration is increased with ageing, while evidence for reduced sleep intensity and consolidation is inconsistent. Here we discuss two possible explanations for these species differences. First, methodological differences between studies in humans and laboratory rodents may prevent straightforward comparison. Second, the role of ecological factors, which have a profound influence on both ageing and sleep, must be taken into account. We propose that the dynamics of sleep across the lifespan reflect both age-dependent changes in the neurobiological substrates of sleep as well as the capacity to adapt to the environment.