Key points

Sleep structure and pattern change with age, sleep typically becoming lighter and more fragmented.

While sleep disorders may not be independently associated with age, they occur more commonly in older people due to co-morbidity.

Common ‘minor’ medical conditions may seriously impair sleep quality.

Neurological conditions such as stroke, Parkinson’s, and dementia are often associated with sleep disorders which can be difficult to treat.

Circadian rhythm disorders are common in older people; primary insomnia is rare.

Respiratory sleep disorders are also common but their significance in many people is uncertain.

Effective treatments are available for restless legs syndrome and related disorders.

1 Introduction

Sleep is an essential physiological process. Neural activity consistent with sleep has been found in animals as simple as the nematode, and no higher animal, to our knowledge, has evolved to the point where it no longer requires sleep. Even creatures such as migrating birds and marine mammals sleep despite the challenges of doing so while flying or swimming.

However, the actual purpose of sleep is still controversial in some respects. In young mammals’ sleep, particularly, rapid eye movement (REM) sleep plays an ontogenetic role in brain and cognitive development. Sleep deprivation in early life can result in behavioural disturbances and even reduction in brain mass in animal models (1–3). Sleep probably has an anabolic and restorative function. Animals suffering prolonged sleep deprivation show an impairment of immune function and those forcibly kept awake have shown immune failure with time. Another restorative function of sleep is in the healing of tissue injury, but it is unclear whether healing occurs faster at night for any reason other than relative immobilization of injured tissue.

Sleep has an important role in processing and recording of memory in humans, although the specifics of the relationship remain controversial. Sleep seems to facilitate the sorting and either retention or ‘unlearning’ of memories that have been accumulated in the recent past. REM sleep appears to have a role in procedural and spatial memory, and, some have suggested, a role in the unconscious ‘rehearsal’ of motor activities. Non-REM, slow-wave sleep appears to have a role in the retention of declarative memory; i.e. memory for facts and figures (semantic memory) and memory for life events (episodic memory). Normal sleep structure changes and evolves throughout the life cycle and in older humans is influenced by numerous physiological, environmental, and pathological factors.

2 Normal sleep in older people

A number of changes in sleep structure and pattern are commonly seen in older people. Whether these changes are truly physiological or are actually pathological but occurring in a very high proportion of the older population is debated. Across an adult lifespan, in healthy individuals, total sleep time decreases by anything up to 90–120 minutes (4) per night. Sleep efficiency—the time in any sleep period spent asleep rather than awake—diminishes, and sleep may become more polyphasic. Sleep becomes more easily interrupted by external stimuli, and periods of wakefulness during sleep become more prolonged. Sleep latency—the time taken to fall asleep—generally remains unchanged, but this is strongly influenced by sleep deprivation in all age groups. Proportion of light stage 1 and 2 sleep increases with age and is matched by a corresponding decrease in deep stage 3 and 4 sleep. Duration of REM sleep declines with declining sleep time, but its proportion of the total is usually maintained. REM sleep latency—the delay from sleep onset to REM sleep—is unchanged. What is perhaps most interesting is that these changes in sleep structure appear to develop in people’s youth and middle age, whereas beyond 60 years there is little change in sleep structure except for a slight (3% per decade) further reduction in sleep efficiency.

It is worth emphasizing that these alterations in sleep pattern are what occurs in healthy subjects and that sleep is profoundly affected by other disease states. Ageing per se is not associated with an increased risk of sleep disorders (5) but is associated with development of frailty and both medical and psychological conditions that impact on sleep. Reported prevalence of sleep disorders in older people varies greatly depending on definitions used and method of study. In the US, sleep disorders are reported by more than 50% of community-dwelling elders and more than two thirds of those in institutional care (6, 7). Sleep disorders and disturbance also frequently contribute to decisions to place older people in institutional care, with between 70 and 80% of carers reporting their own sleep disturbance as influencing their decision (7). Sleep disorders in older people have been reported associated with increased risk of falls, decreased quality of life, and increased mortality (8–10). There may also be an association between sleep disorders, particularly respiratory sleep disorders, and the development of adult onset diabetes. The association was first noted for sleep-disordered breathing (11), but it is now suspected that the association may exist with non-respiratory sleep disorders (12).

3 Common medical and psychiatric disorders and sleep

Sleep disorders in older people commonly occur secondary to other medical conditions. Symptoms, which may be perceived as being ‘minor’ by medical practitioners or relatives, may be enough to significantly disrupt the sleep of an older person to the extent where it affects quality of life and daytime functioning. Examples of such symptoms include gastro-oesophageal reflux, arthritic or neuropathic pain, chronic cough, and nocturia. Poorly controlled diabetes may result in a sufficient nocturnal polyuria to adversely affect sleep quality.

Common neurological conditions can also have direct effects on sleep structure. In the days immediately following stroke, subjects can completely lose the ability to generate REM sleep (13, 14). In the longer term, more than 50% suffer from insomnia and more than one quarter may suffer daytime sleepiness (15, 16). Parasomnias such as restless legs syndrome are also commoner following stroke (17).

Nearly two thirds of people with Parkinson’s disease report sleep problems, twice the rate in control populations (18), and sleep disorders are found in 74–89% of subjects on formal investigation (19). This may be influenced directly by the effect on dopaminergic pathways, which may precipitate sudden sleep attacks, but also indirectly by the immobility associated with the disease and the medications used to treat it. Insomnia, circadian rhythm disorders, parasomnias (as described later in the chapter), and daytime sleepiness are all much more common in individuals with Parkinson’s disease.

Most dementing processes are associated with changes in sleep pattern and structure. Between 40% and 70% of people with dementia have a concomitant sleep disorder on evaluation. Perhaps the most recognized of these among geriatricians is the increasing agitation and confusion suffered by about 10–20% of people with dementia in the late evening, described as ‘sundowning’. This is worsened by the progression of polyphasic sleep and frequent daytime naps in this population as circadian rhythm deteriorates. The evidence for treating sleep disorders in the group is very limited and thus there is widespread use of agents such as antipsychotics and benzodiazepines to help manage the problems. In reality this use is frequently ineffective in improving sleep quality and is actually employed as a means of pharmaceutical restraint. Such use increases risk of falls and fracture and increases mortality (20, 21). Prior to consideration of hypnotic treatment, other interventions can be considered, including behaviour modification; prevention of excessive daytime sleeping; provision of stimulants to wakefulness at appropriate times, such as exposure to bright light in the morning; being taken outside for walks; and establishment and maintenance of a definite daytime routine of rising, dressing, mealtimes at table, etc. While commonly advocated, few of these non-pharmacological therapies have been subjected to robust clinical trials (22). There may be some evidence for the use of melatonin in people with sundowning and delerium (23), although previous studies have failed to show improvement of sleep in institutionalized Alzheimer’s patients with this medication (24). Studies have been small and a larger definitive trial is needed.

Anxiety and depressive disorders are common in older people (10–20% prevalence of each) and it is important to remember that new or recent onset sleep disorder in an older person may be an indicator of the development of neuropsychiatric disease (25–27). The evidence for the effect on sleep quality of treatment of anxiety disorder in older people using anxiolytics is limited. Antidepressants can have complex effects on sleep structure and quality which vary depending on mechanism of action. The newer antidepressant agomelatine, is a melatonin receptor agonist and selective serotonin receptor antagonist and may be superior to selective serotonin reuptake inhibitors in improving sleep quality in subjects with depression (28). Unfortunately, the effects of agomelatine have not been assessed in subjects with dementia and its use is therefore currently restricted to non-demented subjects.

Even where diseases themselves do not cause a sleep disorder, their treatment may. A large proportion of medications have ‘sleep disorders’ listed as potential adverse effects. Commonly used agents to be aware of include corticosteroids, thyroid drugs, angiotensin-converting enzyme inhibitors and statins, all of which have been reported to cause insomnia. Patients prescribed diuretics for hypertension or oedema often complain of insomnia precipitated by nocturia. Even antihistamines, generally accepted as sedating and occasionally used as hypnotics, can cause a paradoxical arousal in a minority of patients. Beta blockers cause disturbing dreams as do leukotriene receptor antagonists, such as montelukast prescribed for asthma. Other commonly used drugs such as tobacco, caffeine, and alcohol may significantly impair sleep quality but are often forgotten when looking for the cause of sleep disturbance.

4 Insomnia and circadian rhythm disorders

Circadian rhythms that dictate the levels of wakefulness and sleepiness in mammals are controlled by the tiny suprachiasmatic nucleus (SCN). With ageing, and particularly in people with neurodegenerative conditions such as Alzheimer’s disease, outputs from the SCN lose synchronization and periodicity and become less effective in modulating arousal level. Thus circadian rhythm disorders are common in older subjects. The commonest disorders seen in older adults are irregular sleep-wake rhythms, particularly in patients with neurodegenerative disease and in those in long-term care with inadequate ‘zeitgebers’—triggers for time and expected sleep-wake status such as clocks, regular mealtimes, and exposure to bright light. Advanced sleep phase disorder (ASPD), where an individual begins to fell sleepy early in the evening but awakens early in the morning, is also more common among older people. Delayed sleep phase disorder is commoner among teenagers and adolescents. Extrinsic circadian rhythm disorders such as jet lag and shift work disorder tend to affect older people more severely. Circadian rhythm disorders are frequently misdiagnosed as insomnia and treated with sedatives, which can actually worsen the problem by further attenuating the effect of the SCN. Recommended treatments include exposing people to daylight or bright light at appropriate times of the day, improving sleep hygiene by reintroducing a daily and bedtime routine and, in the case of ASPD, gradually delaying bedtime by one hour weekly until a normal sleep phase is regained (29, 30).

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