Removal of temporal constraints in the middle-aged and elderly: effects on sleep and sleepiness

Effects of aging on the intrinsic circadian period of totally blind humans

Age-related changes in the intrinsic circadian period (tau) have been hypothesized to account for sleep symptoms in the elderly such as early morning awakening. The authors sought to determine whether the aging process produced quantifiable differences in the tau of totally blind men who had free-running circadian rhythms. The melatonin onset was used as the indicator of circadian phase. Melatonin rhythms had been characterized about a decade previously when the participants were 38 +/- 6 (SD) years old. Both previous and current assessments of tau were derived from at least 3 serial measurements of the 24-h melatonin profile from which the melatonin onset was determined. All 6 participants exhibited a longer tau in the 2nd assessment (mean increase +/- SD of 0.13 +/- 0.08 h; p < 0.01). Four participants exhibited differences in tau with nonoverlapping 95% confidence intervals. The results do not support the commonly held view that tau shortens during human aging. On the contrary, tau appears to slightly, but significantly, lengthen during at least 1 decade in midlife.

Ageing and the circadian and homeostatic regulation of human sleep during forced desynchrony of rest, melatonin and temperature rhythms

1. The circadian timing system has been implicated in age-related changes in sleep structure, timing and consolidation in humans. 2. We investigated the circadian regulation of sleep in 13 older men and women and 11 young men by forced desynchrony of polysomnographically recorded sleep episodes (total, 482; 9 h 20 min each) and the circadian rhythms of plasma melatonin and core body temperature. 3. Stage 4 sleep was reduced in older people. Overall levels of rapid eye movement (REM) sleep were not significantly affected by age. The latencies to REM sleep were shorter in older people when sleep coincided with the melatonin rhythm. REM sleep was increased in the first quarter of the sleep episode and the increase of REM sleep in the course of sleep was diminished in older people. 4. Sleep propensity co-varied with the circadian rhythms of body temperature and plasma melatonin in both age groups. Sleep latencies were longest just before the onset of melatonin secretion and short sleep latencies were observed close to the temperature nadir. In older people sleep latencies were longer close to the crest of the melatonin rhythm. 5. In older people sleep duration was reduced at all circadian phases and sleep consolidation deteriorated more rapidly during the course of sleep, especially when the second half of the sleep episode occurred after the crest of the melatonin rhythm. 6. The data demonstrate age-related decrements in sleep consolidation and increased susceptibility to circadian phase misalignment in older people. These changes, and the associated internal phase advance of the propensity to awaken from sleep, appear to be related to the interaction between a reduction in the homeostatic drive for sleep and a reduced strength of the circadian signal promoting sleep in the early morning.

Changes in circadian rhythms and sleep quality with aging: mechanisms and interventions

Literature is reviewed indicating that aging is characterized by changes in circadian rhythms and sleep quality. The most marked change is an attenuation of amplitude. An advance of phase, a shortening of period, and a desynchronization of rhythms are also evident. The mechanisms underlying these changes are unknown. However, age-related changes in the retina, suprachiasmatic nucleus, and pineal gland seem relevant along with behavioral changes such as a reduction in physical activity and exposure to photic stimulation. Changes in circadian rhythms are frequently associated with a reduction in nighttime sleep quality, a decrease in daytime alertness, and an attenuation in cognitive performance; reversing such changes could enhance the quality of life for a large and rapidly increasing percentage of the population. Reversal appears possible by increasing melatonin levels with either appropriately timed exposure to photic stimulation and/or appropriately timed administration of exogenous melatonin. These interventions may increase aspects of genetic expression that have changed with aging. A hypothesis concerning the potential benefits of enhanced circadian amplitude is also offered.

Alterations in circadian rhythmicity of the vasopressin-producing neurons of the human suprachiasmatic nucleus (SCN) with aging

The suprachiasmatic nucleus (SCN) of the anterior hypothalamus is implicated in the temporal organization of circadian rhythms in a variety of physiological, endocrine and behavioral processes. There is a great deal of evidence indicating that aging is characterized by a progressive deterioration of circadian timekeeping. The present study was aimed at investigating whether there are age-related changes in circadian rhythmicity of the vasopressin (VP)-producing neurons in the human SCN. To that end brains obtained at autopsy of 39 subjects, ranging in age from 6 to 91 years, were studied. Subjects were divided into two age groups, viz. 'young subjects' (up to 50 years) and 'elderly subjects' (over 50 years). It is shown that the number of VP-immunoreactive neurons in the human SCN exhibits a marked diurnal oscillation in young, but not in elderly, people. Whereas in young subjects low VP-immunoreactive neuron numbers were found during the night period (22:00-06:00 h) and peak values during the early morning (06:00-10:00 h), the SCN of elderly people showed a reduced amplitude and a tendency for a reversed diurnal pattern with high instead of low values during the night. The findings suggest that the VP synthesis of the human SCN exhibits a circadian rhythm that is disrupted later in life.

The effect of old age on the free-running period of circadian rhythms in rat

The free-running period is regarded to be an exclusive feature of the endogenous circadian clock. Changes during aging in the free-running period may therefore reflect age-related changes in the internal organization of this clock. However, the literature on alterations in the free-running period in aging is not unequivocal. In the present study, with various confounding factors kept to a minimum, it was found that the free-running periods for active wakefulness, body temperature, and drinking behavior were significantly shorter (by 12-17 min) in old than in young rats. In addition, it was found that the day-to-day stability of the different sleep states was reduced in old rats, whereas that of the drinking rhythm was enhanced. Transient cycles were not observed, nor were there any age-related differences in daily totals of the various sleep-wake states. The amplitudes of the circadian rhythms of active wakefulness, quiet sleep, and temperature were reduced, whereas those of paradoxical sleep and quiet wakefulness remained unchanged.

Circadian rhythms and the suprachiasmatic nucleus in perinatal development, aging and Alzheimer's disease

Circadian rhythms are already present in the fetus. At a certain stage of pre-natal hypothalamic development (around 30 weeks of gestation) the fetus becomes responsive to maternal circadian signals. Moreover, recent studies showed that the fetal biological clock is able to generate circadian rhythms, as exemplified by the rhythms of body temperature and heart rate of pre-term babies in the absence of maternal or environmental entrainment factors. Pre-term babies that are deprived of maternal entrainment and kept under constant environmental conditions (e.g., continuous light) in the neonatal intensive care unit run the risk of developing a biological clock dysfunctioning. However, the fact should be acknowledged that at least in mice the development of the circadian pacemaker (i.e., SCN) does not depend on environmental influences (Davis and Menaker, 1981), although other data suggest that severe disruption of the maternal circadian rhythm indeed abolishes the circadian rhythm of the fetal SCN (Shibata and Moore, 1988). During aging and in particular in AD circadian rhythms are disturbed. These disturbances include phase advance and reduced period and amplitude, as well as an increased intradaily variability and a decreased interdaily stability of the rhythm. Among the factors underlying these changes the loss of SCN neurons seems to play a central role. Other contributory factors may be reduced amount of light, degenerative changes in the visual system and the level of activity and decreased melatonin.

Healthy elderly women and men have different entrained circadian temperature rhythms

Body core temperature was measured in healthy elderly men and women under entrained conditions. Female subjects showed a larger amplitude and a higher peak temperature than male subjects. In addition, acrophase was advanced for females by an average of 49 minutes. Variability in acrophase was greater for males than females. This pattern of gender differences varies considerably from the pattern others have observed in young subjects, suggesting that aging may affect the circadian timing system of males and females differently.

The relationship of chronobiology to sleep schedules and performance demands

This review is concerned with how chronobiological results concerning the human circadian timekeeping system ( biological clock'), its response to changes in schedule, and its influence on performance ability can be used to improve shift worker wellbeing, safety and productivity.

The timing of bedtime and waketime decisions in free-running subjects

Twelve "free-running" temporal isolation studies were performed using healthy human subjects aged 20-81 years (4 males, 8 females). Circadian rhythms were measured in subjective alertness (using a visual analogue scale technique) and rectal temperature. In all 12 subjects best fitting rhythm period were found to be shorter for rectal temperature (mean = 24.3 hours) than for subjective alertness (mean = 24.8 hours). Both rhythms were predictive of bedtime and waketime decisions. Bedtime decisions tended to cluster on the falling arm of the temperature and alertness cycles (modal times = 120 degrees (temperature) and 140 degrees (alertness) after acrophase); waketime decisions on the rising arm (modal times = 240 degrees (temperature) and 300 degrees (alertness) after acrophase). When this pattern was violated, sleep episodes were significantly more variable in length and disturbed by intruding wakefulness.