Many reports have suggested as much as a 50% reduction in REM sleep in older as compared to younger adults.^28,44 However, when the effects of mental and physical illnesses are taken into consideration,³⁶ the percentage of REM sleep is relatively well preserved from age 60 years onward.²⁸

Sleep-related respiratory disorders encompass those conditions that cause abnormal respiratory events during sleep, ranging from mild snoring to a reduction (hypopnea) or complete cessation of airflow (apnea).⁵¹ Obstructive sleep apnea is one of the most common sleep disorders. It is caused by relaxation and subsequent collapse of muscles in the back of the throat, causing obstruction of the upper airway. The increased prevalence of sleep apnea in older adults, which has been reported to be as high as 62% in those older than 60 years,⁵² may be due to the increased occurrence of obesity, age-related decline in muscle tone, or impaired pharyngeal sensory detection thresholds. Sleep apnea often goes unrecognized in older adults because the overt symptoms that are reported—fatigue, daytime sleepiness, morning headache, mood changes, poor concentration, or memory loss—tend to be attributed to other comorbidities or to the aging process.

Peaking at age 50 to 60 years, snoring is also a frequent complaint of older adults. Interestingly, the prevalence of snoring has been shown to decrease after the age of 75 years, possibly reflecting a survivorship effect. Snoring may be related to various comorbidities, especially obesity and sleep-disordered breathing, that ultimately contribute to premature death in this age group. Narrowing of the upper airway, which contributes to snoring, is also associated with the many health consequences of sleep-disordered breathing, including hypertension, heart disease, and stroke.^53–55

Periodic Limb Movements in Sleep and Restless Legs Syndrome

Periodic limb movements are repetitive leg jerks or kicks that occur specifically during sleep. They can range from subtle contractions of the ankle or toe muscles to dramatic flailing of the limbs. These movements often occur during N2, resulting in sleep disruption and excessive daytime sleepiness. Its prevalence increases with age and can be found in as many as 45% of community-dwelling older adults.⁵⁶

Restless legs syndrome is commonly comorbid, and often confused, with period leg movement disorder. It is characterized by uncomfortable, restless, crawling sensations in the legs, creating an irresistible urge to move or walk, typically when one first goes to bed. These sensations can contribute to sleep-onset insomnia as well as disrupted sleep. The condition is also more prevalent in older adults, occurring in up to 35% of those older than 65 years, with about twice as many women being affected. Restless legs syndrome has been associated with iron deficiency and abnormal dopaminergic signaling; it can be treated with interventions aimed at these features.⁵⁷

Rapid Eye Movement Sleep Behavior Disorder

REM sleep behavior disorder involves movement during dreams due to the absence of muscle atonia, which normally occurs during REM sleep.⁵⁸ Individuals may engage in punching, kicking, yelling, or even more elaborate behaviors during REM sleep; the behaviors are often aggressive in nature and can injure the sleeper or bed partner. This condition is relatively rare in the general population (0.5%) and occurs almost exclusively in men older than 60 years.^59,60 The cause of REM sleep behavior disorder is unclear, but has been strongly linked to the subsequent development of neurodegenerative diseases known as synucleinopathies, including Parkinson disease, Lewy body dementia, and multiple system atrophy.⁶¹

Sleep Disturbance and Comorbidity

Despite the characteristic sleep changes that are experienced by older adults, these typically age-associated sleep disturbances may not be an inevitable part of the healthy aging process, but rather a consequence of other changes that accompany aging. Insomnia, in particular, appears to be a major factor contributing to the increase in age-associated sleep complaints.^62–64 However, the decreased ability to fall asleep or maintain sleep once initiated is frequently linked to a comorbid health condition. There is an increased risk for various medical and psychiatric conditions (e.g., depression, diabetes, arthritis, chronic pain, loss of bladder elasticity) during aging, which may indirectly disturb sleep.⁴¹ In addition, pharmacologic treatments for these conditions (e.g., antidepressants, β-blockers, diuretics, corticosteroids) are often not recognized as factors that may contribute to sleep disturbances. Although one study has reported that an extensive health assessment can identify medical conditions that account for most sleep complaints in older adults,³⁶ an estimated 10% to 16% of community-dwelling adults older than 65 years still report chronic (primary) insomnia in the absence of an obvious precipitant.^65,66

Sleep and Frailty

Frailty can be conceptualized as an increasing vulnerability to poor health outcomes (i.e., disability, institutionalization, mortality) as a result of accumulating age-associated declines in physiologic systems; because health deficits increase with age, so does frailty.^67,68 Little is known about the relationship between frailty and sleep or about the consequences of sleep disturbances in frail populations.^69,70 In addition, the sparse literature on this topic has focused primarily on community-dwelling older adults.^25,71–74

Daytime drowsiness is associated with a higher level of frailty,⁷⁴ and older adults who exhibit poor subjective sleep quality, increased nighttime waking, and greater nighttime hypoxemia have been found to be at higher risk for increasing frailty about 3 years later.⁷³ Those with excessive daytime sleepiness, frequent nighttime awakenings, and sleep apnea may also be at greater risk for mortality up to about 3 years later, whereas short sleep duration and prolonged sleep-onset latency are not clearly associated with increased frailty or risk of early death.⁷³ Given that sleep disturbances are associated with poorer health, frail individuals, who are already more vulnerable to the accumulation of stressors, may also be affected by the consequences of sleep impairment to a greater extent than healthy older adults (e.g., responses to sleep medication, impact of insomnia or other sleep disorders). Alterations to the sleep-wake cycle may have prognostic utility in predicting future decline in health and increasing frailty. If so, then treating specific sleep disorders in frail adults may reduce the rate of acquisition of deficits and development of dependency.

Sleep in Critically Ill Older Adults

Patients who are especially susceptible to the adverse effects of accumulating deficits are those in the intensive care unit (ICU). Sleep disturbance and insomnia are common in ICU patients,^75,76 in particular in older adults.⁷⁷ Sleep disruption in the ICU has also been linked to impaired healing and recovery, and even to increased mortality.^78,79 In addition, up to 41% and 96% of older patients in the general and surgical wards, respectively, are prescribed sedative-hypnotic drugs. As discussed later, these drugs tend to have greater negative effects in older adults and may interact adversely with other medications that may also be prescribed for them. Several analyses have concluded that the risk of adverse health outcomes from sedative agents does not justify the small benefit achieved.^80,81 It remains unclear how age and premorbid frailty levels affect sleep quality in older adults who are treated in the ICU.⁸² Determining how sleep quality in this environment affects health outcomes, such as cognitive decline and mortality, will help provide guidance about appropriate treatments for vulnerable older patients in this high-risk situation.