Sleep Disorders in Older Adults
K. Rao Poduri in Geriatric Rehabilitation, 2017
Circadian rhythms, such as core body temperature, hormone secretion, and the sleep–wake cycle, oscillate approximately every 24 hours. In humans, the sleep–wake cycle is regulated by an endogenous pacemaker and exogenous stimuli. The hypothalamic suprachiasmatic nucleus is believed to be this endogenous clock of the brain and is also considered the mediator of circadian rhythms, which are naturally entrained by exogenous stimuli; as people age, their circadian rhythms become weaker, desynchronized, and lose amplitude. It is hypothesized that the deterioration of the suprachiasmatic nucleus and its subsequent weakened functioning contribute to the disruption of circadian rhythms in older adults. The external cues that are necessary to entrain the circadian rhythm of sleep–wake cycles may be weak or missing in older adults. The elderly, especially those who are institutionalized, spend very little time exposed to bright light. Healthy older adults have a daily average of 60 minutes exposure to bright light; those who suffer from Alzheimer and live at home have only 30 minutes, and those who are in nursing homes have 0 minute of bright light exposure zeitgebers (time cues) [8]. The most significant zeitgeber is light.
Circadian Rhythm
Mehwish Iqbal in Complementary and Alternative Medicinal Approaches for Enhancing Immunity, 2023
Several physiological activities are controlled by internal body clocks, including sleep–wake cycles, metabolism, body temperature and feeding. Circadian activities fluctuate with a duration of 24 hours and can continue to fluctuate in the lack of entraining impetus. The clock in mammals is most frequently driven by light by means of input from the retina to the ‘master clock' or hypothalamus SCN (suprachiasmatic nucleus) (Brown & Piggins, 2007). Consumption of food, temperature and other consistently changing factors can also drive circadian behaviour. Under typical 12-hour cycles of darkness and 12-hour cycles of light, ZT0 (zeitgeber time) points out the duration at which lights of the sleeping area are switched on while ZT12 represents the time at which lights are switched off. Typically, humans are most active and alert during the phase of ‘daytime' after ZT0, while the animals who used to awaken at night are most active during the phase of ‘nighttime' subsequent to ZT12. If the elements of the circadian clock are complete and unimpaired, mammals are capable of sustaining strong circadian oscillations in physiological processes and activity for long durations even with the lack of rising stimuli (Downton et al., 2020; Takahashi, 2017).
Entrainment
Sue Binkley in Biological Clocks, 2020
A German word, Zeitgeber, which means “time-giver,” denotes the environmental signals that provide time cues—lighting, temperature, food availability, sound, social factors, etc. In the natural world, most of the potential Zeitgebers should recur at 24 hours (light, high temperature, social activity) and should reinforce one another in entraining a circadian rhythm in those organisms that are sensitive to more than one Zeitgeber.
Time-restricted feeding alters the efficiency of mammary tumor growth
Published in Chronobiology International, 2022
William H. Walker, Alexis L. Kaper, O. Hecmarie Meléndez-Fernández, Jacob R. Bumgarner, Jennifer A. Liu, James C. Walton, A. Courtney DeVries, Randy J. Nelson
As mentioned, light is a powerful zeitgeber (“time giver”), which is responsible for entraining endogenous circadian rhythms to the solar day among humans and other animals. However, light is not the only zeitgeber, as rhythms can also be entrained to timing of food intake, social interaction, and temperature (Golombek and Rosenstein 2010). Indeed, timed feeding can restore rhythmicity in activity rhythms and clock gene expression within the SCN in mice housed in constant darkness or constant light (Castillo et al. 2004; Lamont et al. 2005). Time-restricted feeding mice can shift clock gene expression within the liver and gastrointestinal track independent of the SCN (Hara et al. 2001; Hoogerwerf et al. 2007). Similar to disrupted circadian rhythms, improperly timed feeding has detrimental metabolic consequences (Allison and Goel, 2018; Yoshida et al. 2018). Given that timing of food intake can act as a zeitgeber for the circadian clock, and most individuals in the developed world have access to food at all times of the day in a “24/7” society, we sought to determine the effects on timing of food intake on tumor growth. We hypothesized that time-restricted feeding would alter tumor growth and predicted that improperly timed feeding (i.e., food restricting mice to their inactive phase) would accelerate tumor growth likely via circadian disruption.
Zeitgebers and their association with rest-activity patterns
Published in Chronobiology International, 2019
Mirja Quante, Sara Mariani, Jia Weng, Catherine R Marinac, Emily R Kaplan, Michael Rueschman, Jonathan A Mitchell, Peter James, J. Aaron Hipp, Elizabeth M Cespedes Feliciano, Rui Wang, Susan Redline
Our study is in line with laboratory findings, namely, that the timing of the three exposures of meals, physical activity and light plays a significant role in setting our circadian clock. Light, specifically outdoor light, was the most important zeitgeber determining sleep times and timings of peak activity and inactivity. Numerous studies have shown that light is the most effective environmental signal that sets the central biological clock in the hypothalamus (Arendt and Broadway 1987; Khalsa et al. 2003; Youngstedt et al. 2016). About 20 years ago, Duffy et al. used an inverted schedule of sleep timing, sedentary activity and social contact with or without bright light exposure to test the influence of light to re-set the human circadian system in healthy young men. In contrast to the behavioural events, timed light exposure was very powerful to re-set the human circadian system (Duffy et al. 1996). Thus, our study results reaffirm the role of light as a primary zeitgeber.
Voluntary exercise stabilizes photic entrainment of djungarian hamsters (Phodopus sungorus) with a delayed activity onset
Published in Chronobiology International, 2018
D. Weinert, K. Schöttner, A.C. Meinecke, J. Hauer
Circadian rhythms are generated by an endogenous clock that harbors in the suprachiasmatic nuclei (SCN) in mammals (Dibner et al. 2010; Weaver 1998). As the period length (tau) deviates from the 24-h cycle of the environment, the rhythm has to be synchronized by external cues, so-called zeitgebers (Aschoff 1960). The main zeitgeber for animals and humans is the daily light-dark cycle, though other environmental cues may be important as well (Sharma and Chandrashekaran 2005). Entrainment is achieved by resetting mechanisms, which correct tau and establish a stable phase relationship (phase angle) between the endogenous circadian pacemaker and the external stimulus (Johnson et al. 2003). Particularly, with respect to photic zeitgebers, two models have been developed (Daan 2000), which can be briefly described as follows. Aschoff’s parametric model postulates that light and dark speed up and slow down, respectively, circadian rhythms in diurnal species, the opposite effects taking place in nocturnal animals. Pittendrigh developed the non-parametric model, which postulates that the light-dark and dark-light transitions cause phase changes thereby entraining the circadian rhythms.