Circadian phase resetting in older people by ocular bright light exposure

Circadian Rhythm of Distal Skin Temperature in Healthy Older and Young Women and Its Relationship with Sleep-Wake Rhythm and Environmental Factors under Natural Living Conditions

Little is known about the healthy aging of the circadian timing system under natural living conditions. This study explores changes in the circadian rhythm of distal skin temperature (DST) with aging and relates these changes to sleep-wake timing and environmental influences. DST, sleep-wake timing, 24-h light exposure, and physical activity were measured and averaged over seven consecutive days using temperature sensors, actigraphy with a light meter, and sleep diaries in 35 healthy older women (60-79 years) and 30 young women (20-34 years). Circadian rhythm characteristics, describing strength (amplitude) and timing (acrophase) of the DST rhythm, were calculated using cosinor analysis. The older adults displayed an 18-19% smaller amplitude and a 66-73 min earlier acrophase (peak time) for DST rhythm than the young adults, indicating a weaker and phase-advanced DST rhythm. The phase advance for DST was not due to an earlier evening increase, but to a shorter nocturnal plateau period. Daytime light exposure inversely affected strength (amplitude) but not phasing of the DST rhythm in older adults. The DST rhythm was 3.5 times more advanced than the sleep-wake rhythm, showing an altered phase relationship (phase angle) between both rhythms with aging. The phase angle was more heterogeneous among older adults, showing differential aging. The phase advance for DST rhythm and the altered and heterogeneous phase relationship between DST and sleep-wake rhythms were not related to ambient light exposure and the physical activity of older adults. This suggests that healthy aging of the circadian system might be due to endogenous mechanisms such as an internal rearrangement rather than external influences.

The Stability of Social and Behavioral Rhythms and Unexpected Low Rate of Relevant Depressive Symptoms in Old Adults during the COVID-19 Pandemic

Background: The disruption of social rhythms was found to be associated with depressive disorders during the COVID-19 pandemic; lower rates of these disorders were surprisingly found in old adults. The present study aims to verify the stability of social rhythms during lockdown in a sample of elderly people. Methods: Controlled cohort study (secondary analyses) of a previous randomized-controlled trial with the first evaluation in April 2019 (T0) and then 48 weeks later (T1) during the lockdown. The regulation of social and behavioral rhythms was measured through the Brief Social Rhythms Scale (BSRS); the Patient Health Questionnaire-9 (PHQ9) was adopted to detect relevant depressive symptoms. Results: 93 elderlies (73.36 ± 4.97 years old, 50.5% females) were evaluated at T0 and T1. Neither the total score of BSRS nor any of the 10 items showed a statistically significant difference comparing the two survey periods. The frequency of relevant depressive symptoms was 5.3% at T0 and 6.4% at T1 (OR = 0.8, CI95% 0.2-24). Conclusions: Among elderlies who did not show an increased risk of depression during the lockdown, social and behavioral rhythms remained exceptionally stable during the same period. Considering previous evidence about rhythms dysregulation preceding depression, their stability may be considered a factor of resilience.

A minimal model of peripheral clocks reveals differential circadian re-entrainment in aging

The mammalian circadian system comprises a network of endogenous oscillators, spanning from the central clock in the brain to peripheral clocks in other organs. These clocks are tightly coordinated to orchestrate rhythmic physiological and behavioral functions. Dysregulation of these rhythms is a hallmark of aging, yet it remains unclear how age-related changes lead to more easily disrupted circadian rhythms. Using a two-population model of coupled oscillators that integrates the central clock and the peripheral clocks, we derive simple mean-field equations that can capture many aspects of the rich behavior found in the mammalian circadian system. We focus on three age-associated effects that have been posited to contribute to circadian misalignment: attenuated input from the sympathetic pathway, reduced responsiveness to light, and a decline in the expression of neurotransmitters. We find that the first two factors can significantly impede re-entrainment of the clocks following perturbation, while a weaker coupling within the central clock does not affect the recovery rate. Moreover, using our minimal model, we demonstrate the potential of using the feed-fast cycle as an effective intervention to accelerate circadian re-entrainment. These results highlight the importance of peripheral clocks in regulating the circadian rhythm and provide fresh insights into the complex interplay between aging and the resilience of the circadian system.

Review on age-related differences in non-visual effects of light: melatonin suppression, circadian phase shift and pupillary light reflex in children to older adults

Physiological effects of light exposure in humans are diverse. Among them, the circadian rhythm phase shift effect in order to maintain a 24-h cycle of the biological clock is referred to as non-visual effects of light collectively with melatonin suppression and pupillary light reflex. The non-visual effects of light may differ depending on age, and clarifying age-related differences in the non-visual effects of light is important for providing appropriate light environments for people of different ages. Therefore, in various research fields, including physiological anthropology, many studies on the effects of age on non-visual functions have been carried out in older people, children and adolescents by comparing the effects with young adults. However, whether the non-visual effects of light vary depending on age and, if so, what factors contribute to the differences have remained unclear. In this review, results of past and recent studies on age-related differences in the non-visual effects of light are presented and discussed in order to provide clues for answering the question of whether non-visual effects of light actually vary depending on age. Some studies, especially studies focusing on older people, have shown age-related differences in non-visual functions including differences in melatonin suppression, circadian phase shift and pupillary light reflex, while other studies have shown no differences. Studies showing age-related differences in the non-visual effects of light have suspected senile constriction and crystalline lens opacity as factors contributing to the differences, while studies showing no age-related differences have suspected the presence of a compensatory mechanism. Some studies in children and adolescents have shown that children's non-visual functions may be highly sensitive to light, but the studies comparing with other age groups seem to have been limited. In order to study age-related differences in non-visual effects in detail, comparative studies should be conducted using subjects having a wide range of ages and with as much control as possible for intensity, wavelength component, duration, circadian timing, illumination method of light exposure, and other factors (mydriasis or non-mydriasis, cataracts or not in the older adults, etc.).

Keeping an eye on circadian time in clinical research and medicine

BACKGROUND

Daily rhythms are observed in humans and almost all other organisms. Most of these observed rhythms reflect both underlying endogenous circadian rhythms and evoked responses from behaviours such as sleep/wake, eating/fasting, rest/activity, posture changes and exercise. For many research and clinical purposes, it is important to understand the contribution of the endogenous circadian component to these observed rhythms.

CONTENT

The goal of this manuscript is to provide guidance on best practices in measuring metrics of endogenous circadian rhythms in humans and promote the inclusion of circadian rhythms assessments in studies of health and disease. Circadian rhythms affect all aspects of physiology. By specifying minimal experimental conditions for studies, we aim to improve the quality, reliability and interpretability of research into circadian and daily (i.e., time-of-day) rhythms and facilitate the interpretation of clinical and translational findings within the context of human circadian rhythms. We describe protocols, variables and analyses commonly used for studying human daily rhythms, including how to assess the relative contributions of the endogenous circadian system and other daily patterns in behaviours or the environment. We conclude with recommendations for protocols, variables, analyses, definitions and examples of circadian terminology.

CONCLUSION

Although circadian rhythms and daily effects on health outcomes can be challenging to distinguish in practice, this distinction may be important in many clinical settings. Identifying and targeting the appropriate underlying (patho)physiology is a medical goal. This review provides methods for identifying circadian effects to aid in the interpretation of published work and the inclusion of circadian factors in clinical research and practice.

Associations of circadian rest/activity rhythms with cognition in middle-aged and older adults: Demographic and genetic interactions

Objectives

Wrist actigraphs (accelerometers) can record motor activity over multiple days and nights. The resulting data can be used to quantify 24-h activity profiles, known as circadian rest-activity rhythms (CRARs). Actigraphic CRARs have been tied to cognitive performance and decline in older adults; however, little is known about links between CRARs and performance or change in specific cognitive domains, or how individual differences may influence these associations. We investigated associations of actigraphic CRARs with cognitive performance and change in middle-aged and older adults, and explored whether age, sex/gender, race, and apolipoprotein E (APOE) e4 carrier status moderated these associations.

Materials and methods

Participants (N = 422; 47% male) were cognitively healthy adults (i.e., without mild cognitive impairment or dementia) at baseline aged ≥ 50 years from the Baltimore Longitudinal Study of Aging who completed 5.6 ± 0.89 nights of wrist actigraphy and tests of memory, executive function, attention, language, and visuospatial ability at the same visit the actigraph was issued; 292 participants had repeat cognitive testing 3.12 (1.58) years later. Predictors included indices of rhythm strength [i.e., amplitude; relative amplitude (RA); interdaily stability (IS); mesor], delayed timing of the rhythm peak [i.e., later acrophase; midpoint of an individual's least active 5 h (L5 time); midpoint of an individual's most active 10 h (M10 time)], and fragmentation [i.e., intradaily variability (IV)].

Results

In main effects, later L5 time was cross sectionally associated with poorer memory, and greater IS predicted slower longitudinal memory decline. Associations of CRARs with cognition differed as a function of age, sex/gender, race, and APOE e4 carrier status.

Conclusion

Among middle-aged and older adults, delayed circadian phase is associated with poorer memory performance, and greater day-to-day rhythm stability is associated with slower declines in memory. Significant interactions suggest that CRARs are generally more strongly associated with cognitive performance and rate of cognitive decline among women, Black adults, older individuals, and APOE e4 carriers. Replication in independent samples is needed.

Hilaire MA, Grant LK, Barger LK, Brainard GC, Czeisler CA, Klerman EB, Lockley SW. Dynamic lighting schedules to facilitate circadian adaptation to shifted timing of sleep and wake

Circadian adaptation to shifted sleep/wake schedules may be facilitated by optimizing the timing, intensity and spectral characteristics of light exposure, which is the principal time cue for mammalian circadian pacemaker, and possibly by strategically timing nonphotic time cues such as exercise. Therefore, circadian phase resetting by light and exercise was assessed in 44 healthy participants (22 females, mean age [±SD] 36.2 ± 9.2 years), who completed 8-day inpatient experiments simulating night shiftwork, which included either an 8 h advance or 8 h delay in sleep/wake schedules. In the advance protocol (n = 18), schedules were shifted either gradually (1.6 h/day across 5 days) or abruptly (slam shift, 8 h in 1 day and maintained across 5 days). Both advance protocols included a dynamic lighting schedule (DLS) with 6.5 h exposure of blue-enriched white light (704 melanopic equivalent daylight illuminance [melEDI] lux) during the day and dimmer blue-depleted light (26 melEDI lux) for 2 h immediately before sleep on the shifted schedule. In the delay protocol (n = 26), schedules were only abruptly delayed but included four different lighting conditions: (1) 8 h continuous room-light control; (2) 8 h continuous blue-enriched light; (3) intermittent (7 × 15 min pulses/8 h) blue-enriched light; (4) 8 h continuous blue-enriched light plus moderate intensity exercise. In the room-light control, participants received dimmer white light for 30 min before bedtime, whereas in the other three delay protocols participants received dimmer blue-depleted light for 30 min before bedtime. Both the slam and gradual advance protocols induced similar shifts in circadian phase (3.28 h ± 0.37 vs. 2.88 h ± 0.31, respectively, p = .43) estimated by the change in the timing of timing of dim light melatonin onset. In the delay protocol, the continuous 8 h blue-enriched exposure induced significantly larger shifts than the room light control (-6.59 h ± 0.43 vs. -4.74 h ± 0.62, respectively, p = .02). The intermittent exposure induced ~60% of the shift (-3.90 h ± 0.62) compared with 8 h blue-enriched continuous light with only 25% of the exposure duration. The addition of exercise to the 8 h continuous blue-enriched light did not result in significantly larger phase shifts (-6.59 h ± 0.43 vs. -6.41 h ± 0.69, p = .80). Collectively, our results demonstrate that, when attempting to adapt to an 8 h overnight work shift, delay shifts are more successful, particularly when accompanied by a DLS with high-melanopic irradiance light stimulus during wake.

Circadian Rhythm Sleep-Wake Disorders in Older Adults

The timing, duration, and consolidation of sleep result from the interaction of the circadian timing system with a sleep-wake homeostatic process. When aligned and functioning optimally, this allows for wakefulness throughout the day and a long consolidated sleep episode at night. Changes to either the sleep regulatory process or how they interact can result in an inability to fall asleep at the desired time, difficulty remaining asleep, waking too early, and/or difficulty remaining awake throughout the day. This mismatch between the desired timing of sleep and the ability to fall asleep and remain asleep is a hallmark of a class of sleep disorders called the circadian rhythm sleep-wake disorders. In this updated article, we discuss typical changes in the circadian regulation of sleep with aging; how age influences the prevalence, diagnosis, and treatment of circadian rhythm sleep disorders; and how neurologic diseases in older patient impact circadian rhythms and sleep.

Duration invariance and intensity dependence of the human circadian system phase shifting response to brief light flashes

The melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) are characterized by a delayed off-time following the cessation of light stimulation. Here, we exploited this unusual physiologic property to characterize the exquisite sensitivity of the human circadian system to flashed light. In a 34 h in-laboratory between-subjects design, we examined phase shifting in response to variable-intensity (3-9500 photopic lux) flashes at fixed duration (2 ms; n = 28 participants) and variable-duration (10 µs-10 s) flashes at fixed intensity (2000 photopic lux; n = 31 participants). Acute melatonin suppression, objective alertness and subjective sleepiness during the flash sequence were also assessed. We find a dose-response relationship between flash intensity and circadian phase shift, with an indication of a possible threshold-like behaviour. We find a slight parametric relationship between flash duration and circadian phase shift. Consistent with prior studies, we observe no dose-response relationship to either flash intensity or duration and the acute impact of light on melatonin suppression, objective alertness or subjective sleepiness. Our findings are consistent with circadian responses to a sequence of flashes being mediated by rod or cone photoreceptors via ipRGC integration.

Investigation of the aging clock's intermittent-light responses uncovers selective deficits to green millisecond flashes

The central pacemaker of flies, rodents, and humans generates less robust circadian output signals across normative aging. It is not well understood how changes in light sensitivity might contribute to this phenomenon. In the present study, we summarize results from an extended data series (n = 5681) showing that the locomotor activity rhythm of aged Drosophila can phase-shift normally to intermittently spaced episodes of bright polychromatic light exposure (600 lx) but that deficits emerge in response to 8, 16, and 120-millisecond flashes of narrowband blue (λ_m, 452 nm) and green (λ_m, 525 nm) LED light. For blue, phase-resetting of the activity rhythm of older flies is not as energy efficient as it is in younger flies at the fastest flash-exposures tested (8 milliseconds), suggesting there might be different floors of light duration necessary to incur photohabituation in each age group. For green, the responses of older flies are universally crippled relative to those of younger flies across the slate of protocols we tested. The difference in green flash photosensitivity is one of the most salient age-related phenotypes that has been documented in the circadian phase-shifting literature thus far. These data provide further impetus for investigations on pacemaker aging and how it might relate to changes in the circadian system's responses to particular sequences of light exposure tuned for wavelength, intensity, duration, and tempo.

Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.

Sleep in Normal Aging, Homeostatic and Circadian Regulation and Vulnerability to Sleep Deprivation

In the context of geriatric research, a growing body of evidence links normal age-related changes in sleep with many adverse health outcomes, especially a decline in cognition in older adults. The most important sleep alterations that continue to worsen after 60 years involve sleep timing, (especially early wake time, phase advance), sleep maintenance (continuity of sleep interrupted by numerous awakenings) and reduced amount of sigma activity (during non-rapid eye movement (NREM) sleep) associated with modifications of sleep spindle characteristics (density, amplitude, frequency) and spindle-Slow Wave coupling. After 60 years, there is a very clear gender-dependent deterioration in sleep. Even if there are degradations of sleep after 60 years, daytime wake level and especially daytime sleepiness is not modified with age. On the other hand, under sleep deprivation condition, older adults show smaller cognitive impairments than younger adults, suggesting an age-related lower vulnerability to extended wakefulness. These sleep and cognitive age-related modifications would be due to a reduced homeostatic drive and consequently a reduced sleep need, an attenuation of circadian drive (reduction of sleep forbidden zone in late afternoon and wake forbidden zone in early morning), a modification of the interaction of the circadian and homeostatic processes and/or an alteration of subcortical structures involved in generation of circadian and homeostatic drive, or connections to the cerebral cortex with age. The modifications and interactions of these two processes with age are still uncertain, and still require further investigation. The understanding of the respective contribution of circadian and homeostatic processes in the regulation of neurobehavioral function with aging present a challenge for improving health, management of cognitive decline and potential early chronobiological or sleep-wake interventions.

The aging brain: sleep, the circadian clock and exercise

Aging is a multifactorial process likely stemming from damage accumulation and/or a decline in maintenance and repair mechanisms in the organisms that eventually determine their lifespan. In our review, we focus on the morphological and functional alterations that the aging brain undergoes affecting sleep and the circadian clock in both human and rodent models. Although both species share mammalian features, differences have been identified on several experimental levels, which we outline in this review. Additionally, we delineate some challenges on the preferred analysis and we suggest that a uniform route is followed so that findings can be smoothly compared. We conclude by discussing potential interventions and highlight the influence of physical exercise as a beneficial lifestyle intervention, and its effect on healthy aging and longevity. We emphasize that even moderate age-matched exercise is able to ameliorate several aging characteristics as far as sleep and circadian rhythms are concerned, independent of the species studied.

Nocturnal Melatonin Suppression by Adolescents and Adults for Different Levels, Spectra, and Durations of Light Exposure

The human circadian system is primarily regulated by the 24-h LD cycle incident on the retina, and nocturnal melatonin suppression is a primary outcome measure for characterizing the biological clock's response to those light exposures. A limited amount of data related to the combined effects of light level, spectrum, and exposure duration on nocturnal melatonin suppression has impeded the development of circadian-effective lighting recommendations and light-treatment methods. The study's primary goal was to measure nocturnal melatonin suppression for a wide range of light levels (40 to 1000 lux), 2 white light spectra (2700 K and 6500 K), and an extended range of nighttime light exposure durations (0.5 to 3.0 h). The study's second purpose was to examine whether differences existed between adolescents' and adults' circadian sensitivity to these lighting characteristics. The third purpose was to provide an estimate of the absolute threshold for the impact of light on acute melatonin suppression. Eighteen adolescents (age range, 13 to 18 years) and 23 adults (age range, 24 to 55 years) participated in the study. Results showed significant main effects of light level, spectrum, and exposure duration on melatonin suppression. Moreover, the data also showed that the relative suppressing effect of light on melatonin diminishes with increasing exposure duration for both age groups and both spectra. The present results do not corroborate our hypothesis that adolescents exhibit greater circadian sensitivity to short-wavelength radiation compared with adults. As for threshold, it takes longer to observe significant melatonin suppression at lower CS levels than at higher CS levels. Dose-response curves (amount and duration) for both white-light spectra and both age groups can guide lighting recommendations when considering circadian-effective light in applications such as offices, schools, residences, and healthcare facilities.

Phase Shifts to a Moderate Intensity Light Exposure in Older Adults: A Preliminary Report

Age-related disrupted sleep has been associated with modifications in the timing of endogenous circadian rhythms. There are studies suggesting a decreased sensitivity of the aging circadian pacemaker to light. In this study, we aimed to test whether a moderate illuminance light stimulus would produce significant phase shifts in older adults, and whether those would fall in a range consistent with the illuminance response curve (IRC) we previously reported in older adults. We conducted an 8-day in-patient study with 12 healthy older participants (mean age [SD], 58.3 [4.2] y, 5 females). A 6.5-h polychromatic white light exposure with a target illuminance of 270 lux was administered beginning in the early biological night. Before and after the light exposure, a circadian phase estimation procedure was carried out, with plasma melatonin data used as a circadian phase marker. The mean phase delay produced by the light stimulus was 1.78 ± 0.77 h. Ten of the 12 phase delay shifts at ~270 lux fell within the 95% predictive interval of the model fit to data from our previous IRC in older adults. This finding demonstrates that the circadian system of healthy older adults is sensitive to the phase-delaying effects of a moderate intensity light stimulus. The magnitude of the observed phase shifts is consistent with the previously described IRC in older adults.

Impact of a shift work-like lighting schedule on the functioning of the circadian system in the short-lived fish Nothobranchius furzeri

Adult Nothobranchius furzeri of the MZM-04/10 strain were individually kept and subjected to a "5 + 2" shifting lighting schedule (SHIFT) for 8 weeks in order to evaluate the desynchronizing effects of a simulated human-like shift-work schedule on the functioning of the circadian system (CS). With this aim, sixteen 21-week-old N. furzeri were placed into a Morning, Night and Evening schedule (lights on from 08:00 to 16:00, 00:00 to 08:00 and 16:00 to 00:00 h, respectively) and fed once a day in the middle of the corresponding photophase (12:00, 04:00 and 20:00 h, respectively). Then, in the weekends (2 days), fish were always returned to the Morning shift. As controls, 16 fish were maintained under a non-shifting LD cycle condition (CONTROL) throughout the whole experiment, with lights on from 08:00 to 16:00 h. Rest-activity rhythm (RAR) of fish subjected to SHIFT showed several symptoms of chronodisruption, such as a decrease in the percentage of diurnal activity and a reduction of the relative amplitude and the circadian function index with time. When a periodogram analysis was performed, RAR of N. furzeri under SHIFT conditions showed up to three separate circadian components: one longer than 24 h (26.5 h) that followed the weekly 8 h delays; a short-period component (~23 h) that was related to the weekend's phase advances, and finally, a 24 h component. The shifting LD schedule also affected fish CS at a molecular level, with several significant differences in the expression of core genes of the molecular clock (bmal1, clock, rorα, rev-erbα) between SHIFT and CONTROL animals. RAR impairment along with changes in clock gene expression could be associated with high stress and accelerated aging in these fish.

Scheduled evening sleep and enhanced lighting improve adaptation to night shift work in older adults

OBJECTIVES

We tested whether a sleep and circadian-based treatment shown to improve circadian adaptation to night shifts and attenuate negative effects on alertness, performance and sleep in young adults would also be effective in older adults.

METHODS

We assessed subjective alertness, sustained attention (psychomotor vigilance task, PVT), sleep duration (actigraphy) and circadian timing (salivary dim-light melatonin onset, DLMO) in 18 older adults (57.2±3.8 years; mean±SD) in a simulated shift work protocol. 4 day shifts were followed by 3 night shifts in the laboratory. Participants slept at home and were randomised to either the treatment group (scheduled evening sleep and enhanced lighting during the latter half of night shifts) or control group (ad-lib sleep and typical lighting during night shifts).

RESULTS

Compared with day shifts, alertness and sustained attention declined on the first night shift in both groups, and was worse in the latter half of the night shifts. Alertness and attention improved on nights 2 and 3 for the treatment group but remained lower for the control group. Sleep duration in the treatment group remained similar to baseline (6-7 hours) following night shifts, but was shorter (3-5 hours) following night shifts in the control group. Treatment group circadian timing advanced by 169.3±16.1 min (mean±SEM) but did not shift (-9.7±9.9 min) in the control group.

CONCLUSIONS

The combined treatment of scheduled evening sleep and enhanced lighting increased sleep duration and partially aligned circadian phase with sleep and work timing, resulting in improved night shift alertness and performance.

Are Modifications of Melatonin Circadian Rhythm in the Middle Years of Life Related to Habitual Patterns of Light Exposure?

The mechanisms underlying age-related changes in the signal from the biological clock have yet to be determined. The authors sought to determine if the phase advance of circadian melatonin rhythm during the middle years of life is related to different patterns of habitual light exposure. Forty-one healthy subjects between the ages of 22 and 58 y were studied. Habitual light exposure was measured by a wrist monitor for 7 days. Participants underwent a 25-h constant routine. They provided saliva samples every 30 min, and melatonin concentration was determined by radioimmunoassay to assess salivary dim light melatonin onset (S-DLMO1.3). Aging was associated with earlier S-DLMO1.3. Increasing age was not related to the time spent at different light intensities. However, it was associated with lower percentage of light exposure during the night (between 0200-0400, 0600-0700, and 2300-2400 h) and with higher percentage of light exposure in the morning (between 0800-1100 h). Earlier S-DLMO1.3 was associated with lower percentage of light exposure early on in the night (between 2200-0000, 0000-0100, and 0200-0300 h) as well as in the afternoon (between 1500-1600 h) and with higher percentage of light exposure in the morning (between 0800-1100 h). When the effects of age were controlled, there was no significant relationship between S-DLMO1.3 and percentages of light exposure. Yet increasing age was associated with earlier S-DLMO1.3 regardless of light exposure patterns. Earlier habitual wake time explained the earlier light exposure patterns of older subjects. Both habitual wake time and age contributed to the prediction of S-DLMO1.3. The results suggest a phase advance of circadian rhythms in the middle years of life. Whereas a clear change in habitual light exposure patterns was associated with aging and with shifts in S-DLMO1.3, it did not explain entirely the age-related advance of melatonin circadian phase.

Light-sensitive brain pathways and aging

Notwithstanding its effects on the classical visual system allowing image formation, light acts upon several non-image-forming (NIF) functions including body temperature, hormonal secretions, sleep-wake cycle, alertness, and cognitive performance. Studies have shown that NIF functions are maximally sensitive to blue wavelengths (460–480 nm), in comparison to longer light wavelengths. Higher blue light sensitivity has been reported for melatonin suppression, pupillary constriction, vigilance, and performance improvement but also for modulation of cognitive brain functions. Studies investigating acute stimulating effects of light on brain activity during the execution of cognitive tasks have suggested that brain activations progress from subcortical regions involved in alertness, such as the thalamus, the hypothalamus, and the brainstem, before reaching cortical regions associated with the ongoing task. In the course of aging, lower blue light sensitivity of some NIF functions has been reported. Here, we first describe neural pathways underlying effects of light on NIF functions and we discuss eye and cerebral mechanisms associated with aging which may affect NIF light sensitivity. Thereafter, we report results of investigations on pupillary constriction and cognitive brain sensitivity to light in the course of aging. Whereas the impact of light on cognitive brain responses appears to decrease substantially, pupillary constriction seems to remain more intact over the lifespan. Altogether, these results demonstrate that aging research should take into account the diversity of the pathways underlying the effects of light on specific NIF functions which may explain their differences in light sensitivity.

Melatonin and Sleep-Wake Rhythms before and after Ocular Lens Replacement in Elderly Humans

Light of short wavelengths has been shown to play a key role in non-image forming responses. Due to aging, the ocular lens becomes more yellow reducing the transmission of short wavelengths in the elderly. In the present study, we make use of cataract surgery to investigate the effects of a relative increase of short wavelength transmission on melatonin- and sleep-wake rhythms (N = 14). We observed, on average, a delay of the sleep-wake and the nocturnal melatonin rhythms after cataract surgery. This delay is tentatively attributed to a relatively large increase of light transmittance in the evening hours more than an increase of the already relatively high light intensities found in the daytime. The later phase that we observed after cataract surgery (clear lens) as compared to the earlier phase observed before cataract (yellowish lens) is in agreement with the general later phase reported in the young (clear lens) population.

Aging and Circadian Rhythms

Aging is associated with numerous changes, including changes in sleep timing, duration, and quality. The circadian timing system interacts with a sleep-wake homeostatic system to regulate human sleep, including sleep timing and structure. This article reviews key features of the human circadian timing system, age-related changes in the circadian timing system, and how those changes may contribute to the observed alterations in sleep.

Genetic background influences age-related decline in visual and nonvisual retinal responses, circadian rhythms, and sleep

The circadian system is entrained to the environmental light/dark cycle via retinal photoreceptors and regulates numerous aspects of physiology and behavior, including sleep. These processes are all key factors in healthy aging showing a gradual decline with age. Despite their importance, the exact mechanisms underlying this decline are yet to be fully understood. One of the most effective tools we have to understand the genetic factors underlying these processes are genetically inbred mouse strains. The most commonly used reference mouse strain is C57BL/6J, but recently, resources such as the International Knockout Mouse Consortium have started producing large numbers of mouse mutant lines on a pure genetic background, C57BL/6N. Considering the substantial genetic diversity between mouse strains we expect there to be phenotypic differences, including differential effects of aging, in these and other strains. Such differences need to be characterized not only to establish how different mouse strains may model the aging process but also to understand how genetic background might modify age-related phenotypes. To ascertain the effects of aging on sleep/wake behavior, circadian rhythms, and light input and whether these effects are mouse strain-dependent, we have screened C57BL/6J, C57BL/6N, C3H-HeH, and C3H-Pde6b+ mouse strains at 5 ages throughout their life span. Our data show that sleep, circadian, and light input parameters are all disrupted by the aging process. Moreover, we have cataloged a number of strain-specific aging effects, including the rate of cataract development, decline in the pupillary light response, and changes in sleep fragmentation and the proportion of time spent asleep.

Absence of central circadian pacemaker abnormalities in humans with loss of function mutation in prokineticin 2

CONTEXT

Loss of prokineticin 2 (PROK2) signaling in mice disrupts circadian rhythms, but the role of PROK2 signaling in the regulation of circadian rhythms in humans is undetermined.

OBJECTIVE

The aim of the study was to examine the circadian rhythms of humans with a complete loss-of-function PROK2 mutation using an inpatient constant routine (CR) protocol.

DESIGN AND SETTING

We conducted a case study in an academic medical center.

SUBJECTS AND METHODS

Two siblings (one male and one female, ages 67 and 62 y, respectively) with isolated GnRH deficiency (IGD) due to a biallelic loss-of-function PROK2 mutation were studied using an inpatient CR protocol. Historical data from inpatient CR protocols conducted in healthy controls (ages 65-81 y) were used for comparison.

MAIN OUTCOME MEASURES

We measured circadian phase markers (melatonin, cortisol, and core body temperature) and neurobehavioral performance (psychomotor vigilance task [PVT] and subjective alertness scale).

RESULTS

Circadian waveforms of melatonin and cortisol did not differ between the IGD participants with PROK2 mutation and controls. In both IGD participants, neurobehavioral testing with PVT showed disproportionate worsening of PVT lapses and median reaction time in the second half of the CR.

CONCLUSIONS

Humans with loss of PROK2 signaling lack abnormalities in circadian phase markers, indicating intact central circadian pacemaker activity in these patients. These results suggest that PROK2 signaling in humans is not required for central circadian pacemaker function. However, impaired PVT in the PROK2-null participants despite preserved endocrine rhythms suggests that PROK2 may transmit circadian timing information to some neurobehavioral neural networks.

Aging reduces the stimulating effect of blue light on cognitive brain functions

STUDY OBJECTIVES

Light exposure, particularly blue light, is being recognized as a potent mean to stimulate alertness and cognition in young individuals. Aging is associated with changes in alertness regulation and cognition. Whether the effect of light on cognitive brain function changes with aging is unknown, however.

DESIGN

Cross-sectional study.

SETTING

Functional Neuroimaging Unit, University of Montreal Geriatric Institute.

PARTICIPANTS

Sixteen younger (23 ± 4.1 y) and 14 older (61 ± 4.5 y) healthy participants were recruited in the current study.

INTERVENTION

Blue light administration.

MEASUREMENTS

We used functional magnetic resonance imaging to record brain responses to an auditory working memory task in young and older healthy individuals, alternatively maintained in darkness or exposed to blue light.

RESULTS

Results show that the older brain remains capable of showing sustained responses to light in several brain areas. However, compared to young individuals, the effect of blue light is decreased in the pulvinar, amygdala, and tegmentum as well as in the insular, prefrontal, and occipital cortices in elderly individuals.

CONCLUSION

The effect of blue light on brain responses diminishes with aging in areas typically involved in visual functions and in key regions for alertness regulation and higher executive processes. Our findings provide the first indications that the effect of light on cognition may be reduced in healthy aging.

Phase-shifting response to light in older adults

Age-related changes in circadian rhythms may contribute to the sleep disruption observed in older adults. A reduction in responsiveness to photic stimuli in the circadian timing system has been hypothesized as a possible reason for the advanced circadian phase in older adults. This project compared phase-shifting responses to 2 h of broad-spectrum white light at moderate and high intensities in younger and older adults. Subjects included 29 healthy young (25.1 ± 4.1 years; male to female ratio: 8: 21) and 16 healthy older (66.5 ± 6.0 years; male to female ratio: 5: 11) subjects, who participated in two 4-night and 3-day laboratory stays, separated by at least 3 weeks. Subjects were randomly assigned to one of three different time-points, 8 h before (-8), 3 h before (-3) or 3 h after (+3) the core body temperature minimum (CBTmin) measured on the baseline night. For each condition, subjects were exposed in a randomized order to 2 h light pulses of two intensities (2000 lux and 8000 lux) during the two different laboratory stays. Phase shifts were analysed according to the time of melatonin midpoint on the nights before and after light exposure. Older subjects in this study showed an earlier baseline phase and lower amplitude of melatonin rhythm compared to younger subjects, but there was no evidence of age-related changes in the magnitude or direction of phase shifts of melatonin midpoint in response to 2 h of light at either 2000 lux or 8000 lux. These results indicate that the acute phase-shifting response to moderate- or high-intensity broad spectrum light is not significantly affected by age.

Aging of the suprachiasmatic clock

More than half of the elderly in today's society suffer from sleep disorders with detrimental effects on brain function, behavior, and social life. A major contribution to the regulation of sleep stems from the circadian system. The central circadian clock located in the suprachiasmatic nucleus of the hypothalamus is like other brain regions subject to age-associated changes. Age affects different levels of the clock machinery from molecular rhythms, intracellular messenger, and membrane properties to neuronal network synchronization. While some of the age-sensitive components of the circadian clock, like ion channels and neurotransmitters, have been described, little is known about the underlying mechanisms. In any case, the result is a reduction in the amplitude of the circadian timing signal produced by the suprachiasmatic nucleus, a weakening in the control of peripheral oscillators and a decrease in amplitude and precision of daily rhythms in physiology and behavior. The distortion in temporal organization is thought to be related to a number of serious health problems and promote neurodegeneration. Understanding the mechanisms underlying age-related deficits in circadian clock function will therefore not only benefit rhythm disorders but also alleviate age-associated diseases aggravated by clock dysfunction.

Survival analysis indicates that age-related decline in sleep continuity occurs exclusively during NREM sleep

A common complaint of older persons is disturbed sleep, typically characterized as an inability to return to sleep after waking. As every sleep episode (i.e., time in bed) includes multiple transitions between wakefulness and sleep (which can be subdivided into rapid eye movement [REM] sleep and non-REM [NREM] sleep), we applied survival analysis to sleep data to determine whether changes in the "hazard" (duration-dependent probability) of awakening from sleep and/or returning to sleep underlie age-related sleep disturbances. The hazard of awakening from sleep--specifically NREM sleep--was much greater in older than in young adults. We found, however, that when an individual had spontaneously awakened, the probability of falling back asleep was not greater in young persons. Independent of bout length, the number of transitions between NREM and REM sleep stages relative to number of transitions to wake was approximately 6 times higher in young than older persons, highlighting the difficulty in maintaining sleep in older persons. Interventions to improve age-related sleep complaints should thus target this change in awakenings.

Analysis method and experimental conditions affect computed circadian phase from melatonin data

Accurate determination of circadian phase is necessary for research and clinical purposes because of the influence of the master circadian pacemaker on multiple physiologic functions. Melatonin is presently the most accurate marker of the activity of the human circadian pacemaker. Current methods of analyzing the plasma melatonin rhythm can be grouped into three categories: curve-fitting, threshold-based and physiologically-based linear differential equations. To determine which method provides the most accurate assessment of circadian phase, we compared the ability to fit the data and the variability of phase estimates for seventeen different markers of melatonin phase derived from these methodological categories. We used data from three experimental conditions under which circadian rhythms - and therefore calculated melatonin phase - were expected to remain constant or progress uniformly. Melatonin profiles from older subjects and subjects with lower melatonin amplitude were less likely to be fit by all analysis methods. When circadian drift over multiple study days was algebraically removed, there were no significant differences between analysis methods of melatonin onsets (P = 0.57), but there were significant differences between those of melatonin offsets (P<0.0001). For a subset of phase assessment methods, we also examined the effects of data loss on variability of phase estimates by systematically removing data in 2-hour segments. Data loss near onset of melatonin secretion differentially affected phase estimates from the methods, with some methods incorrectly assigning phases too early while other methods assigning phases too late; missing data at other times did not affect analyses of the melatonin profile. We conclude that melatonin data set characteristics, including amplitude and completeness of data collection, differentially affect the results depending on the melatonin analysis method used.

Aging and circadian disruption: causes and effects

The relationship between aging and daily “circadian” behavior in humans is bidirectional: on the one hand, dysfunction of circadian clocks promotes age-related maladies; on the other, aging per se leads to changes and disruption in circadian behavior and physiology. For the latter case, recent research suggests that changes to both homeostatic and circadian sleep regulatory mechanisms may play a role. Could hormonal changes be in part responsible?

Reduced phase-advance of plasma melatonin after bright morning light in the luteal, but not follicular, menstrual cycle phase in premenstrual dysphoric disorder: an extended study

The authors previously observed blunted phase-shift responses to morning bright light in women with premenstrual dysphoric disorder (PMDD). The aim of this study was to determine if these findings could be replicated using a higher-intensity, shorter-duration light pulse and to compare these results with the effects of an evening bright-light pulse. In 17 PMDD patients and 14 normal control (NC) subjects, the authors measured plasma melatonin at 30-min intervals from 18:00 to 10:00 h in dim (<30 lux) or dark conditions the night before (Night 1) and after (Night 3) a bright-light pulse (administered on Night 2) in both follicular and luteal menstrual cycle phases. The bright light (either 3000 lux for 6 h or 6000 lux for 3 h) was given either in the morning (AM light), 7 h after the dim light melatonin onset (DLMO) measured the previous month, or in the evening (PM light), 3 h after the DLMO. In the luteal, but not in the follicular, phase, AM light advanced melatonin offset between Night 1 and Night 3 significantly less in PMDD than in NC subjects. The effects of PM light were not significant, nor were there significant effects of the light pulse on melatonin measures of onset, duration, peak, or area under the curve. These findings replicated the authors' previous finding of a blunted phase-shift response to morning bright light in the luteal, but not the follicular, menstrual cycle phase in PMDD compared with NC women, using a brighter (6000 vs. 3000 lux) light pulse for a shorter duration (3 vs. 6 h). As the effect of PM bright light on melatonin phase-shift responses did not differ between groups or significantly alter other melatonin measures, these results suggest that in PMDD there is a luteal-phase subsensitivity or an increased resistance to morning bright-light cues that are critical in synchronizing human biological rhythms. The resulting circadian rhythm malsynchonization may contribute to the occurrence of luteal phase depressive symptoms in women with PMDD.

Light treatment prevents fatigue in women undergoing chemotherapy for breast cancer

PURPOSE

Fatigue is one of the most disturbing complaints of cancer patients and is often the reason for discontinuing treatment. This randomized controlled study tested the hypothesis that increased morning bright light, compared to dim light, would result in less fatigue in women with breast cancer undergoing chemotherapy.

METHODS

Thirty-nine women newly diagnosed with stage I-III breast cancer were randomized to either bright white light (BWL) or dim red light (DRL) treatment and were instructed to use the light box for 30 min every morning throughout the first four cycles of chemotherapy. The Multidimensional Fatigue Symptom Inventory was administered prior to the start of chemotherapy (baseline), during the chemotherapy treatment week of cycle 1 (C1TW), the last week (recovery week) of cycle 1 (C1RW), the chemotherapy treatment week of cycle 4 (C4TW), and the last week (recovery week) of cycle 4 (C4RW).

RESULTS

The DRL group reported increased fatigue at C1TW (p = 0.003) and C4TW (p < 0.001) compared to baseline, while there was no significant change from baseline in the BWL group. A secondary analysis showed that the increases in fatigue levels in the DRL group were not mediated through nor associated with changes in sleep or in circadian rhythms as measured with wrist actigraphy.

CONCLUSIONS

The results of this study suggest that morning bright light treatment may prevent overall fatigue from worsening during chemotherapy. Although our hypothesis that overall fatigue would improve with bright light treatment was not supported, the lack of deterioration in total fatigue scores suggests that bright morning light may be a useful intervention during chemotherapy for breast cancer.

The normalization of the cortisol awakening response and of the cortisol shift profile across consecutive night shifts--an experimental study

This study tested the hypothesis that the cortisol awakening response (CAR) and the cortisol shift profile normalize with successive night shifts due to the shift of the circadian system. 18 students (9 women, 9 men, 19-29 years), worked first four consecutive morning- and then four consecutive night shifts. Each work shift was preceded by an 8-h sleep opportunity meaning that the sleep-activity cycle was advanced by 8 h. The advance of the circadian system was promoted by a 2-h bright light pulse at the end of each night shift and quantified by 24-h phase assessment procedures (PA) before and after the four day shifts and again after the four night shifts. Saliva samples were taken 0, 15, 30, 45, and 60 min post-awakening, hourly during each work shift and each PA. During the night shift sequence, the CAR, indicated by the area under curve with respect to increase (AUC(I)), increased gradually across the 4-day sleep periods. Baseline levels were reached after 3 days in men and 4 days in women. The increase of the CAR was associated with a gradually increasing decline of cortisol levels during the night shifts. This adjustment was--at least not only--related to the advance of the circadian system which was 5 h. A contributor to the increase of the CAR might be the anticipation of the upcoming demands of the following work shifts.

Systemic and cellular reflections on ageing and the circadian oscillator: a mini-review

From circulation to digestion to excretion, a circadian clock synchronizes most aspects of mammalian physiology with the solar day. During normal ageing, this daily coordination gradually erodes, and during pathological ageing such erosion is exacerbated. Recent experiments suggest that therapies aimed at sustaining circadian function increase quality of life in elderly patients. Hence, a better understanding of the interactions between the circadian clock and ageing - at both cellular and systemic levels - could lead to direct benefits for aged individuals.

Sleep in care homes

Sleep problems in older adults are common and disturbance in sleep is associated with increased mortality. These problems are more pronounced in the care home population because of institutional factors and a high prevalence of frailty and co-morbidity. This article reviews the randomized controlled trials undertaken to address sleep problems in care homes. These suggest that stand-alone therapies – oral melatonin and light therapy – have no effect on sleep but that combination treatments – physical exercise plus sleep hygiene, physical exercise plus sleep hygiene plus light and melatonin plus light – may have positive effects. These effects are more marked for daytime arousal than nocturnal sleep. Practical considerations for care homes are how to maximize light exposure, incorporate exercise into daily routines and minimize night-time disruption for residents. Trials undertaken so far are compromised by small sample size and inappropriate randomization strategies and further research is therefore required.

Light exposure patterns in healthy older and young adults

Aging is associated with an earlier timing of circadian rhythms and a shorter phase angle between wake time and the timing of melatonin secretion or the core body temperature nadir. Light has a phase-dependent effect on the circadian pacemaker, and modifications of habitual light exposure in older people could contribute to a change in the timing of circadian rhythms or in the phase angle of entrainment. In this study, we compare natural light exposure of community-dwelling older and young subjects studied at the same time of year, focusing on the pattern of light exposure across the waking day. We recorded light exposure data for 3 to 8 days from 22 older (aged 66.01 +/- 5.83) and 22 young subjects (aged 23.41 +/- 4.57), living at home on self-selected sleepwake schedules, and matched for time of year. All subjects were from New England (latitude 42.3 degrees N to 43 degrees N). We compared the percentage of the waking day spent by older and young subjects at 4 different light levels (from very dim to very bright). We compared hourly averaged light exposure data in each group according to clock time and with respect to each subject's daily sleepwake times. Although both age groups spent more than half of their waking hours in dim or moderate room light intensity (<100 lux), we found that the older subjects spent a significantly greater percentage of their waking day in the brighter light levels (> or =1000 lux); their hourly averaged light exposure levels were also significantly greater whether we examined the data with respect to absolute clock time, to wake time, or to bed time, and this was true across all seasons. We found that healthy older people were exposed to significantly higher levels of light throughout their waking day than young people. Differences in natural light exposure may contribute to the age-related phase advance of the circadian pacemaker and its later timing relative to the sleepwake cycle. This hypothesis should be explored further in carefully designed prospective studies.

PERIOD3, circadian phenotypes, and sleep homeostasis

Circadian rhythmicity and sleep homeostasis contribute to sleep phenotypes and sleep-wake disorders, some of the genetic determinants of which are emerging. Approximately 10% of the population are homozygous for the 5-repeat allele (PER3(5/5)) of a variable number tandem repeat polymorphism in the clock gene PERIOD3 (PER3). We review recent data on the effects of this polymorphism on sleep-wake regulation. PER3(5/5) are more likely to show morning preference, whereas homozygosity for the four-repeat allele (PER3(4/4)) associates with evening preferences. The association between sleep timing and the circadian rhythms of melatonin and PER3 RNA in leukocytes is stronger in PER3(5/5) than in PER3(4/4). EEG alpha activity in REM sleep, theta/alpha activity during wakefulness and slow wave activity in NREM sleep are elevated in PER3(5/5). PER3(5/5) show a greater cognitive decline, and a greater reduction in fMRI-assessed brain responses to an executive task, in response to total sleep deprivation. These effects are most pronounced during the late circadian night/early morning hours, i.e., approximately 0-4h after the crest of the melatonin rhythm. We interpret the effects of the PER3 polymorphism within the context of a conceptual model in which higher homeostatic sleep pressure in PER3(5/5) through feedback onto the circadian pacemaker modulates the amplitude of diurnal variation in performance. These findings highlight the interrelatedness of circadian rhythmicity and sleep homeostasis.

Sleep in the elderly: normal variations and common sleep disorders

The most common complaints of older adults concern their difficulty initiating or maintaining sleep, which results in insufficient sleep and an increased risk of falls, difficulty with concentration and memory, and overall decreased quality of life. Difficulties sleeping are not, however, an inevitable part of aging. Rather, the sleep complaints are often comorbid with medical and psychiatric illness, associated with the medications used to treat those illnesses, or the result of circadian rhythm changes or other sleep disorders. Health care professionals specializing in geriatrics need to learn to recognize the different causes of sleep disturbances in this population and to initiate appropriate treatment. Nonpharmacological treatment techniques are discussed; pharmacological treatments are discussed in a companion article.

Age-Related Changes in Acute and Phase-Advancing Responses to Monochromatic Light

Reduced sensitivity to short-wavelength (blue) light with age has been shown for light-induced melatonin suppression. The current research aimed to determine if a similar age-related reduction occurs in subjective alertness, mood, and circadian phase-advancing responses. Young ( n = 11, 23.0 ± 2.9 years) and older ( n = 15, 65.8 ± 5.0 years) healthy males participated in laboratory sessions that included a 2-h intermittent monochromatic light exposure, individually timed to begin 8.5 h after their dim light melatonin onset (DLMO) determined in a prior visit. In separate sessions, pupil-dilated subjects were exposed to short-wavelength blue (λ max 456 nm) and medium-wavelength green (λmax 548 nm) light matched for photon density (6 × 1013 photons/cm2/sec). Subjective alertness, sleepiness, and mood were verbally assessed every 15 to 30 min before, during, and up to 5 h after the light exposure. The magnitude of phase advance was assessed as the difference in plasma melatonin rhythm phase markers before and after light exposure. Following blue light exposure, responses in older men were significantly diminished compared with young men for subjective alertness ( p < 0.0001), sleepiness ( p < 0.0001), and mood ( p < 0.05) during and after light exposure. There was no significant effect of age on these parameters following green light exposure. The phase advances to both blue and green light were larger in the young than older subjects, but did not reach statistical significance. In general, phase advances to blue light were slightly larger than to green light in both young and old, but did not reach statistical significance. The current results add to previous findings demonstrating reduced responsiveness to the acute effects of blue light in older people (melatonin suppression, alertness). However, under the study paradigm, the phase-advancing response to light does not appear to be significantly impaired with age.

Circadian phase response curves to light in older and young women and men

Background

The phase of a circadian rhythm reflects where the peak and the trough occur, for example, the peak and trough of performance within the 24 h. Light exposure can shift this phase. More extensive knowledge of the human circadian phase response to light is needed to guide light treatment for shiftworkers, air travelers, and people with circadian rhythm phase disorders. This study tested the hypotheses that older adults have absent or weaker phase-shift responses to light (3000 lux), and that women's responses might differ from those of men.

Methods

After preliminary health screening and home actigraphic recording baselines, 50 young adults (ages 18–31 years) and 56 older adults (ages 59–75 years) remained in light-controlled laboratory surroundings for 4.7 to 5.6 days, while experiencing a 90-min ultra-short sleep-wake cycle. Following at least 30 h in-lab baseline, over the next 51 h, participants were given 3 treatments with 3000 lux white light, each treatment for 3 h, centered at one of 8 clock times. The circadian rhythms of urinary aMT6s (a melatonin metabolite), free cortisol, oral temperature, and wrist activity were assessed at baseline and after treatment.

Results

Light (3000 lux for 3 h on 3 days) induced maximal phase shifts of about 3 h. Phase shifts did not differ significantly in amplitude among older and young groups or among women and men. At home and at baseline, compared to the young, the older adults were significantly phase-advanced in sleep, cortisol, and aMT6s onset, but not advanced in aMT6s acrophase or the temperature rhythm. The inflection from delays to advances was approximately 1.8 h earlier among older compared to young participants in reference to their aMT6s rhythm peaks, and it was earlier in clock time.

Conclusion

In these experimental conditions, 3000 lux light could shift the phase of circadian rhythms to about the same extent among older and young adults, but the optimal light timing for phase shifting differed. For an interval near 4 PM, bright light produced only negligible phase shifts for either age group.

Sincronização não-fótica: o efeito do exercício físico aeróbio

As principais alterações, agudas e crônicas, provocadas pelo exercício físico aeróbio (EF) sobre o organismo são, de maneira geral, bem conhecidas. No entanto, existe um efeito em particular do EF que começou a ser elucidado no começo da década de 90, em humanos, que tem a capacidade de alterar a relação temporal do organismo com o meio. A modificação da expressão dos ritmos circadianos, causada pelo EF, qualifica-o como sincronizador dos osciladores biológicos. O principal sincronizador da ritmicidade biológica é o ciclo geofísico claro/escuro. A alternância do dia e da noite, através de diferenças nos níveis de luminosidade, é percebida por meio de vias fóticas pelo sistema de temporização circadiana (STC). Esses estímulos, chamados fóticos, fornecem informações temporais para o STC sincronizando os osciladores biológicos com esse ciclo ambiental. Outros estímulos também são capazes de sincronizá-los e são chamados de sincronizadores não-fóticos. Esta revisão aborda o efeito do EF sobre o sistema de temporização e, ao mesmo tempo, discute as possíveis e prováveis aplicações cronobiológicas dos conhecimentos abordados. O EF pode afetar o STC através de vias não-fóticas, podendo beneficiar a saúde de indivíduos em diversas situações, tais como vôos transmeridianos, trabalhos noturnos e distúrbios do sono. Ressalta-se, também, que devem ser realizados mais estudos no cotidiano das pessoas para compreender melhor a relação entre, e a contribuição dos, diferentes sincronizadores em um contexto real.

Jet lag: trends and coping strategies

The number of travellers undertaking long-distance flights has continued to increase. Such flights are associated with travel fatigue and jet lag, the symptoms of which are considered here, along with their similarities, differences, and causes. Difficulties with jet lag because of sleep loss and decreased performance are emphasised. Since jet lag is caused mainly by inappropriate timing of the body clock in the new time zone, the pertinent properties of the body clock are outlined, with a description of how the body clock can be adjusted. The methods, both pharmacological and behavioural, that have been used to alleviate the negative results of time-zone transitions, are reviewed. The results form the rationale for advice to travellers flying in different directions and crossing several time zones. Finally, there is an account of the main problems that remain unresolved.

Decreased sensitivity to phase-delaying effects of moderate intensity light in older subjects

Aging is associated with a change in the relationship between the timing of sleep and circadian rhythms, such that the rhythms occur later with respect to sleep than in younger adults. To investigate whether a difference in the phase-delaying response to evening light contributes to this, we conducted a 9-day inpatient study in 10 healthy older (> or =65 y.o.) subjects. We assessed circadian phase in a constant routine, exposed each subject to a 6.5h broad-spectrum light stimulus beginning in the early biological night, and reassessed circadian phase. The stimuli spanned a range from very dim (approximately 2 lx) to very bright (approximately 8000 lx) indoor light. We found a significant dose-response relationship between illuminance and the phase shift of the melatonin rhythm, with evidence that sensitivity, but not the maximal response to light, differed from that of younger adults. These findings suggest an age-related reduction in the phase-delaying response to moderate light levels. However, our findings alone do not explain the altered phase relationship between sleep and circadian rhythms associated with aging.

Diagnosis and treatment of sleep disorders in older adults

Among the most common complaints of older adults are difficulty initiating or maintaining sleep. These problems result in insufficient sleep at night, which then results in an increased risk of falls, difficulty with concentration and memory, and overall decreased quality of life. Difficulties sleeping, however, are not an inevitable part of aging. Rather, these sleep complaints are often secondary to medical and psychiatric illness, the medications used to treat these illnesses, circadian rhythm changes, or other sleep disorders. The task for the geriatric psychiatrist is to identify the causes of these complaints and then initiate appropriate treatment.

Responsiveness of the aging circadian clock to light

The present study assessed whether advances in sleep times and circadian phase in older adults might be due to decreased responsiveness of the aging circadian clock to light. Sixteen young (29.3+/-5.6 years) and 14 older adults (67.1+/-7.4 years) were exposed to 4h of control dim (10lux) or bright light (3500lux) during the night. Phase shifts of the melatonin rhythm were assessed from the nights before and after the light exposure. Bright light delayed the melatonin midpoint in both young and older adults (p<0.001). Phase delays for the older subjects were not significantly different from those of the young subjects for either the bright or dim light conditions. The magnitude of phase delays was correlated with both sleep offset and phase angle in the older, but not the younger subjects. The present results indicate that at light intensities commonly used in research as well as clinical practice older adults are able to phase delay to the same extent as younger subjects.

Aging human circadian rhythms: conventional wisdom may not always be right

This review discusses the ways in which the circadian rhythms of older people are different from those of younger adults. After a brief discussion of clinical issues, the review describes the conventional wisdom regarding age-related changes in circadian rhythms. These can be summarized as four assertions regarding what happens to people as they get older: 1) the amplitude of their circadian rhythms reduces, 2) the phase of their circadian rhythms becomes earlier, 3) their natural free-running period (tau) shortens, and 4) their ability to tolerate abrupt phase shifts (e.g., from jet travel or night work) worsens. The review then discusses the empirical evidence for and against these assertions and discusses some alternative explanations. The conclusions are that although older people undoubtedly have earlier circadian phases than younger adults, and have more trouble coping with shift work and jet lag, evidence for the assertions about rhythm amplitude and tau are, at best, mixed.