Sleep in Normal Aging (2024)

The publisher's final edited version of this article is available at Sleep Med Clin

Sleep duration

The current literature supports that, in general, the total sleep time (TST) decreases with age (from pediatric to older adulthood). However, further age-associated decreases in TST have not been consistently observed after entering older age brackets. Campbell et al. 2007 conducted a laboratory study with 50 healthy adults aged between 19 and 81 years to evaluate the spontaneous sleep across the 24h day among young, middle-aged, and older adults. Compared with young adults (10.5 hours), middle-aged (9.1 hours) and older adults (8.1 hours) had significantly shorter average nighttime sleep duration.⁵ Data from 160 healthy adults (without sleep complaints) aged between 20 and 90 from the SIESTA database showed that TST decreased about 8 minutes per decade in males and 10 minutes per decade in females.⁶ Similarly, three meta-analysis reviews reported that age was linearly associated with decreased TST, with an approximately 10 – 12 minutes reduction per decade of age in the adult population.^2,7,8 This association was stronger when comparing young adults with middle-aged or older adults, but vanished within older subjects who were 60 years and above. These findings indicate that TST plateaued after 60 years of age. Also, the association was stronger in women than men.²

Sleep initiation

People commonly assume that the ability to initiate sleep declines significantly with age. However, current evidence does not support this assumption but suggests that both sleep latency and the ability to fall back to sleep after nocturnal awakenings demonstrate minimal increases after age greater than 60 years. Results from two meta-analyses, for example, suggest that sleep latency does increase with age. However, the magnitude of change is very modest.^2,8 In these studies, sleep latency holds constant from childhood to adolescence. The significant age-related increase in sleep latency was only found between very young adults and older adults. A mathematical modeling, which was conducted using data from seven laboratory sleep studies (258 subjects aged 17 to 91 years), suggested that sleep latency increased between late teens and twenties, remains constant from age 30 until approximate age 50 years, and then increased steadily after age 50 years.⁹ However, the amount or magnitude of changes were not reported. In addition, even though more frequent arousals were found in healthy older adults than young people, older adults maintained their ability to reinitiate sleep and fell back to sleep as rapidly as younger adults.^3,10

Sleep efficiency

Sleep efficiency remains largely unchanged from childhood to adolescence and significantly decreases with age in adulthood. Different from all other sleep parameters that hold steady after 60 years of age, sleep efficiency continues to decline very slowly with advancing age.²

Sleep maintenance

Aging from birth to older adulthood is associated with decreased ability to maintain sleep, which presents as the increased number of arousals (arousal index) and longer duration of wake after sleep onset (WASO), but also tends to plateau after age 60.^2,8 In Ohayon and colleagues’ meta-analysis, age-related change in WASO achieved the largest effect size among all sleep parameters, which yielded a steady 10 minutes increase of WASO per decade of age from 30 to 60 years. WASO remained mostly unchanged after age 60 years.²

Sleep stages

In general, deep sleep (slow wave sleep) decreases with age in the adult population. During nocturnal sleep, the proportion of non-rapid eye movement sleep (NREM) stage 1 and stage 2 increases with age, and the proportion of slow-wave sleep and REM sleep decreases with age^2,11 (see Figure 1). These changes were not significant among healthy older adults aged above 60 years². Also, the association between age and decreased REM latency was minimal.² Floyd et. al.’s meta-analysis reported a linear decrease in the proportion of REM with a small rate of 0.6% per decade from age 19 until 75 years, then small increases were found in the proportion of REM between 75 and 85 years.⁷

There may be gender differences in age-related changes in sleep stages. Ohayon et al.’s meta-analysis suggested that the age effect on the percentage of stage 1 sleep was stronger in women, and women had less percentage of stage 2 sleep and a greater percentage of SWS than age-matched men. The SIESTA study found that women had no change in SWS with age, in contrast to men who had a 1.7% decrease in SWS per decade of age. In addition, women had a smaller rate of increase in Stage 1 sleep, a greater rate of increase in stage 2 sleep, and a greater rate of decline in REM, in comparison with men.⁶ These results indicate that men may be more prone to age-related decline in SWS than women.

Daytime napping and daytime sleepiness

Daytime napping is a daily routine for many people across the lifespan. Results from epidemiology studies suggest that daytime napping is more prevalent in older adults than that seen in younger adults.^12–15 Several studies hav found that older adults nap more frequently than younger and middle-aged adults,^14,16,17 this is also true when comparing healthy older adults with younger individuals.¹⁸ Within the older population, one study found that nap frequency increased with age.¹⁹ A recent study using 7664 people, aged 20–99 years, from a national representative sample of Japan, found that a higher proportion of older adults (27.4%) take frequent naps (≥4 days/week) than young (11.9%) and middle-aged (14.4%) adults.¹⁴ However, no clear evidence supports that nap duration is different between older adults and other adult populations.^5,19 Campbell et al. 2007’s laboratory study showed that nap durations were not different among the young, middle-aged, and older adults, but the number of daytime naps increased with age.⁵ Yoon and colleagues reported that older adults tended to nap at a different time than younger adults, where older adults were more likely to nap in the early evening, while younger adults were more likely to nap in the afternoon.^18,20

People choose to take a nap for many reasons, such as to compensate for nighttime sleep loss, to restore energy and reduce daytime sleepiness, or just to relax.²⁰ Cultural background also has a considerable influence on nap habits. For example, mid-day naps are a common practice of people from China, Mediterranean and several Latin-American countries.²¹ Older adults may nap more frequently due to both biological changes but also lifestyle changes that accompany aging. For example, older adults may spend less time on work, physical, and social activity, thus have more opportunities to nap than young and middle-aged adults during the day. Also, Foley and colleagues found that frequent napping was associated with excessive daytime sleepiness (EDS), depression, pain and nocturia in a U.S. nationally representative poll of older adults.²²

Epidemiological studies indicated that up to 20% of older adults reported EDS.^23–26 EDS usually co-exists with multiple adverse health conditions, including cognitive impairment, cardiovascular events, and increased mortality risk.^27,28 Certainly, EDS is not a part of normal aging, but may be a signal or symptom of certain diseases. An epidemiological study found a linear decline in the prevalence of EDS with age between 30 and 75 years. In addition, the prevalence of EDS dropped at a higher rate after the age of 75 years.²⁹ Daytime napping could be a practice to reduce daytime sleepiness,¹⁵ however, some older adults may experience daytime sleepiness but do not fall asleep during the day.²⁶

Self-reported sleep quality

People may expect that older adults complain more about their sleep than younger aged adults since most objectively measured sleep parameters decline with age. However, this may not be the case as there can be significant differences between objective and self-reported perceptions of sleep, and comorbidities can play a major role. For example, while some epidemiological studies found that up to 50% of older adults have self-reported poor sleep,^30,31 a large proportion of these complaints are attributable to older adults’ poor health status and disease burden.^30,32 Evidence shows that older adults were less likely to self-report poor sleep than younger individuals, especially after controlling for comorbidities and health.³³ Vitiello and colleagues examined objectively measured sleep among 150 healthy older adults who reported no sleep problems and found that significant proportions of them (33% of women and 16% of men) had impaired objectively measured sleep.³⁰ Healthy older adults may be prone to perceive good sleep quality.³⁴ In addition, older adults may expect their sleep will be less consolidated as they age, and they may accept some noticeable sleep changes as a part of normal aging due to an adjustment of their perception of “acceptable” health with aging.^33,35

As described above, many sleep characteristics change with age in adulthood. For example, noctural sleep duration, sleep effiency, slow wave sleep, and self-reported poor sleep decrease with age; while, number of awakenings, WASO, and daytime napping freqency increase with age. However, most of these changes stop at approximately 60 years of age. After that age, most sleep variables appear to remain largely unchanged within the older adult population.

Phase advance

The timing and structure of sleep are mainly regulated by the circadian system and homeostatic sleep regulation.³⁸ Older adults commonly experience an advance of sleep schedule to earlier hours. They tend to have sleepiness earlier in the evening and wake up earlier in the morning than desired.³⁶ This earlier sleep timing in older adults may be due to the age-related phase advance in their circadian rhythm. This phase advance is seen not only in the sleep-wake cycle, but also in the body temperature rhythm, and in the timing of secretion of melatonin and cortisol,^39–41 all of which are about one hour advanced in older people compared to young adults.⁴²Figure 2 compares circadian phase between older and younger adults. However, Duffy and colleagues found that the phase advance in sleep timing was greater than phase advance in other circadian clocks, which suggested that a mechanism (e.g. sleep homeostasis) other than circadian phase advance alone may be involved in older adult’s early sleep timing.⁴³

Reduced amplitude in circadian rhythms

Aging is associated with a reduction in the amplitude of several circadian rhythms in older adults, including core body temperature, melatonin, and cortisol secretion, activity, and sleep.^44–47 The age-related reduction in circadian amplitude may be related to sleep disruption in older adults.⁴⁸ It was reported that, compared to young adults, older adults were more likely to wake up close to the timing when body temperature reached nadir.⁴⁹ This finding indicated that the biological clock (e.g., body temperature) in older adults might also regulate their awakening time, which may result in even earlier awakenings in older adults.^36,49 Also, the reduced amplitude of daytime activity may result in daytime napping, which may further reduce the amplitude of the sleep-wake rhythm. Age-related decline in amplitude of melatonin secretion may also play a role in sleep problems in older adults.^50,51 (as described below).

Decreased ability adjusting to phase-shifting

The ability to phase-shift deceases with aging.⁵² Older adults are subject to more difficulties in adjusting to phase shifts, such as shift work and jet lag.^4,52 Monk and colleagues found that older adults needed more time to recover from phase-shifting, and experienced a longer period of sleep disruption and daytime disfunction.⁵³ The age-related loss of rhythmic function within the SCN may partially explain this impaired ability in phase shifting.⁵⁴

Changes in sleep homeostasis

Some research indicates that the earlier sleep timing and less consolidated sleep in older adults may be attributable to the interaction between the circadian system and homeostatic regulation, rather than simply resulting from an age-related phase advance in circadian rhythm.^6,55 Sleep homeostasis regulates wake and sleep and generates sleep pressure as a function of time of being awake. Sleep pressure increases during waking and sleep deprivation, and decreases during sleep.⁵⁶ Sleep homeostasis declines with aging. The age-related decrease in TST and sleep efficiency may be partially due to the reduced homeostatic sleep pressure with aging.^57–59 Also, this reduced homeostatic sleep pressure contributes to an increased number of nocturnal awakenings and reduced daytime sleepiness.^58,59 For example, one study that forced desynchronized circadian cycles found that older adults had 2.7 times more nocturnal awakenings than young individuals at most circadian phases.¹⁰

Growth hormone

Growth hormone (GH) secretion and slow wave sleep impact each other.^60,61 GH secretion mainly pulses during nocturnal sleep (no matter whether the sleep is advanced, delayed, or fragmented) at about 1 hour after sleep onset and decreases at transient awakenings.⁶² On the other hand, the inhibition of growth hormone releasing hormone (GHRH) suppresses GH secretion, promotes corticotrophin releasing hormone, and reduces SWS.^62,63 Further, there is an age-related decline in GH secretion.^64,65 GH secretion reaches its peak during adolescence, rapidly declines in an exponential manner between young adulthood and middle age, and then declines slowly between middle to old age. This phenomenon is similar to the detected age-related decrease of SWS.⁶⁶ The decline in nocturnal GH with aging may have a direct or indirect impact on SWS, and may be partially responsible for the observed reduction of SWS in aging.

Cortisol

Cortisol secretion has a clear circadian pattern, which peaks shortly after the morning awakening, gradually declines throughout the day and reaches its nadir in the late evening, and then rises towards the morning peak.⁶⁶ Sleep, particularly SWS, inhibits cortisol secretion.^67,68 The rise of cortisol secretion during sleep could lead to awakenings.^68,69 The circadian rhythm of cortisol changes with aging, as manifested by a decreased circadian amplitude, an elevated nocturnal cortisol level, and likely a phase advanced rhythm.^63,70,71 The elevated nocturnal cortisol level may contribute to decreased SWS and frequent awakenings during nocturnal sleep in older adults.⁷⁰

Prolactin

No clear evidence shows that the secretion of prolactin affects sleep. However, sleep has an influence on prolactin secretion.⁷⁰ Sleep onset is associated with an increased secretion of prolactin, regardless of day or night sleep.⁶⁶ Also, decreased SWS or fragmented sleep may be associated with a reduced elevation of prolactin during nocturnal sleep.⁶⁶ Studies show increased prolactin secretion during SWS or by enhancing SWS, and decreased prolactin secretion in prolonged awakening during the sleep period.^72,73 Prolactin secretion during sleep may decrease with aging due to the lighter and more fragmented sleep in older adults. Studies suggest that nocturnal prolactin in healthy older adults was significantly lower than that in young adults.^65,74

Thyroid-stimulating hormone

Thyroid-stimulating hormone (TSH) secretion has a circadian pattern, which maintains a stable low level during the daytime, starts rising in the late afternoon, peaks around sleep onset, and then gradually declines through the night, and returns to its daytime level after morning awakenings.^66,75 Studies have shown that SWS was associated with inhibited nocturnal TSH secretion, and awakenings were associated with increased nocturnal TSH secretion.^76–78 The circadian release of TSH (with regards to acrophase and nadir) is maintained with aging.⁷⁰ However, research suggets the overall 24-hour TSH secretion is decreased in older adults.⁷⁹

Melatonin

The 24-hour profile of plasma melatonin is primarily regulated by the light-dark circle and the sleep-wake cycle.⁶⁶ Melatonin normally remains stable at a low level during the daytime, starts to increase progressively in the evening (2 hours before habitual bedtime) and remains elevated during the middle of the sleep period, and then drops gradually to its daytime level in the morning (8–9 am).⁶⁶ The onset of evening sleepiness correlates with the rise of evening melatonin secretion. Overall melatonin secretion decreases with aging, but daytime melatonin (which is already at a low basal level) may remain unchanged with aging. The elevation of nocturnal melatonin in older adults was significantly reduced when compared with young adults.^50,80 Studies suggest that the age-related decline in melatonin secretion contributes to the increased sleep disruption in older adults.⁵⁰

Sex hormones

Changes in gonadotropins and sex steroids with aging are associated with sleep changes in older adults. In men, testosterone levels decrease progressively with aging after 30 years of age.^81,82 Older men may also lose the diurnal testosterone pattern.⁸³ The decreased testosterone with aging may relate to the increased sleep fragmentation in older adults.⁷⁰ In women, estradiol levels decrease and follicle stimulating hormone levels increase significantly during the menopause transition and postmenopause. These changes in reproductive hormones have been associated with increased complaints of difficulty falling asleep and staying asleep.⁷⁰ Also, the decreased levels of endogenous estrogen and progesterone may have a negative impact on the upper airway, therefore, increasing the incidence of sleep disordered breathing (SDB) after menopause.⁸⁴

Medical comorbidities and psychiatric illness

Approximately 67% of older adults have multiple comorbidities.⁸⁵ Osteoarthritis, cardiovascular disease, lung disease, gastroesophageal reflux, cancer, and diabetes are the most commonly reported medical comorbidities in older adults.^4,86 About 90% of adults aged 65 and older take prescription drugs to treat their chronic medical conditions. More than one-third of them routinely take over five medications.^87,88 The discomfort and emotional distress from medical conditions contribute to an increased number of nocturnal awakenings and EDS in older adults. Also, chronic medical conditions are positively associated with the diagnosis or prevalence of sleep disorders, including insomnia, sleep apnea, and restless legs syndrome.⁸⁹ Of note, not only do these medical conditions cause sleep disturbances in older adults, but the sleep disturbances can also have a negative impact on medical illnesses and their associated symptoms. Evidence also shows that the multiple medications that older adults take can result in EDS, worsen primary sleep disorders, and contribute to comorbid insomnia.^89,90

Depression and anxiety, prevalent psychiatric problems among older adults, commonly coexist with insomnia in older adults. Epidemiological studies reported that more than 50% of older adults with depression have insomnia. Further, longitudinal studies have found that insomnia may increase the risk of depression in older adults. In addition, depression has been positively associated with EDS, and the diagnosis and severity of obstructive sleep apnea.⁹⁰

Primary sleep disorders

Several primary sleep disorders, which are common in older adults, contribute to poor sleep in older adults. These sleep disorders include insomnia, sleep-disordered breathing, periodic limb movements in sleep, restless legs syndrome, and REM sleep behavior disorder. Epidemiological studies found that the prevalence of these primary sleep disorders is considerably higher in older adults than that in younger adults.^91,92 Medical and psychological comorbidities of aging contribute to the increased prevalvance of insomina symptoms (approximately 50%) in older adults. Interestingly, the prevalence of insomnia in older adults with excellent health is similar to that of younger adults.⁹³ The increase in SDB frequency in older adults may partially be due to an age-related reduction in pharyngeal muscle function and an increase in comorbidities in older adults.⁹⁴ The presentation of these primary sleep disorders contribute to poor sleep in older adults, in terms of difficulties in falling asleep, increased number of nocturnal awakenings, EDS, and complaints of non-restorative sleep.⁹¹

Social, lifestyle, and environmental factors

Many social and lifestyle change with aging contribute to sleep problems in older adults. Retired older adults have more flexible sleep schedules (which can be be irregular), have more opportunity to nap during the day, are more sedentary, and are less involved in social activity than they used to be.^95,96 These factors affect both sleep homeostasis and circadian regulation, thus contributing to sleep disturbances. In addition, the loss of loved ones can produce emotional distress and loneliness, which are known to contribute to sleep disturbance.⁴ Environmentally, many older adults, especially those who have multiple morbidities, lose independence in activities of daily living, and may move to new homes or long-term care facilities. This transition can be a major life event in later life and create several physical and psychological stressors. Sleep problems can rise or get worse during and after this transition. Finally, other environmental factors, such as temperature, noise, and light exposure, are also associated with sleep quality in older adults.^97,98

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