SECTION 4 - SLEEP AND HEALTH

Sleep and Aging

Background

Aging is associated with changes in sleep amount, sleep quality, and specific sleep pathologies and disorders. For instance, increased age is associated with increased prevalence of insomnia complaints, daytime sleepiness, Sleep-Disordered Breathing (SDB), Restless Legs Syndrome (RLS), and Periodic Limb Movement Disorder (PLMD) (Section V). Insomnia alone affects about a third of the older population in the United States. Nocturnal sleep difficulties can result in excessive daytime sleepiness, attention and memory problems, depressed mood, and lowered quality of life. Evidence also suggests that SDB has been associated with dementia and cognitive deficits in the elderly.

Other factors associated with aging, including medical and psychiatric disorders, changes in environment, and psychosocial stressors such as bereavement can also be independent contributors to sleep problems. Sleep disturbances can also lead to changes in physiological systems, especially production of appropriate hormone levels and proper metabolic functioning. In addition, the circadian regulation of sleep-wake rhythms is altered with age, such that older adults sleep at an earlier phase of their circadian cycle (Section I). These changes are seen in the sleep of the healthy elderly unrelated to complaints about disturbed sleep, but are magnified in those with medical and neuropsychiatric disorders (Section V). Disrupted sleep-wake patterns are also a major source of stress among caregivers of patients with dementia, whether in the home or in institutions. Treatments for sleep problems in the elderly can also be associated with morbidity including, for example, the association between hypnotic use and falls or hip fractures.

Recent neuroscience findings regarding sleep regulation have largely focused on young, healthy organisms, and have not explored how age modifies these regulatory mechanisms, or whether such age-related changes can be modified. In humans, there is little consensus regarding which sleep changes are normative developmental changes, and which changes are pathological. This has direct implications for identifying when an intervention is advisable. Given the potential for greater risk of adverse effects in the elderly, there is also a need to develop a broader range of efficacious, safe treatments for all sleep disorders. This issue is particularly salient for individuals with significant medical or neuropsychiatric comorbidity.

Progress in the Last Five Years

- Epidemiologic studies have identified consistent risk factors for late-life Insomnia, and have examined the course of this disorder (Section V). In addition, the epidemiology of SDB in older adults has been well described (Section V). SDB has also been identified as a risk factor for adverse cardiovascular outcomes in the elderly, including hypertension and coronary heart disease.

- Excessive daytime sleepiness, a possible marker for SDB, has been found to be associated with diagnosis of incident dementia and incident cognitive decline three years later, after adjusting for age and other factors. In contrast, Insomnia is not associated with either incident cognitive decline or dementia.

- The period of endogenous circadian rhythms in healthy older persons does not differ from that of healthy young adults. However, older individuals have greater difficulty sleeping at specific circadian phases, which may account for some of the increased sleep complaints seen in aging.

- Behavioral and psychological interventions have been found to be efficacious and durable treatments for older adults with Insomnia. On the other hand, behavioral and environmental interventions have shown limited efficacy among institutionalized individuals with dementia.

- Evidence supporting the efficacy of melatonin for treating Insomnia in the elderly is equivocal. Low doses of melatonin that raise blood levels to the normal young adult nighttime range significantly improve sleep quality in individuals suffering from age-related insomnia in some studies, but not in others.

- Studies have shown the important sleep regulatory functions of a hypothalamic circuit involving the ventro-lateral preoptic nucleus (VLPO). No differences in numbers of VLPO neurons are noted with increasing age, nor are there any differences in levels of adenosine A1 receptor mRNA. Age, however, may affect adenosine receptor function rather than number. While the suprachiasmatic nucleus (SCN) appears to function normally with aging, aging may impair the function of both entrainment (afferent) systems and target (efferent) systems downstream from the SCN.

Research Recommendations

- Investigate the neurobiological mechanisms of age effects on sleep, particularly those related to homeostatic and circadian mechanisms. Circadian studies should investigate the neurobiological causes and consequences of age-related changes in circadian rhythm parameters other than period (e.g., amplitude, waveform), which may be directly related to changes in SCN output or efferent pathways and downstream effector systems. Both basic science and human studies are needed. Genetic, neuroanatomic, neurophysiologic, and neurochemical approaches may be useful in such studies. Conversely, studies investigating the potential effects of sleep, circadian regulation, and sleep disorders on the aging process and the diseases associated with late age are also a high priority.

- Test the efficacy and effectiveness of sleep disorder treatments among individuals with a broader range of medical comorbidities, e.g., individuals with "usual" aging. These studies should include conditions such as Insomnia and SDB, and populations such as nursing home residents.

- Develop a range of novel, safe, and efficacious treatments for sleep disorders in the elderly. These may include the development of new behavioral, pharmacologic, hormonal, behavioral, and physical/environmental (e.g., light) treatments for conditions such as Insomnia, sleep-wake disruptions in dementia, and SDB. Long-term trials investigating the efficacy and adverse effects of pharmacologic and behavioral/ psychological treatments for Insomnia are needed in older patients with both primary and secondary forms of insomnia. The use of techniques such as pharmacogenomics should be employed to identify which treatments are likely to be most efficacious in specific patients or populations (Section I).

- Better define the boundaries of normal and abnormal age-related sleep changes, as well as guidelines for intervention. Examples include defining normative age-related changes in sleep, and thresholds for when SDB or periodic limb movements during sleep require intervention.

- Better define the prevalence of specific sleep disorders in aging. Such studies should employ clinical diagnostic criteria for sleep disorders as well as polysomnographic monitoring. The relationships between sleep disorders and cognitive decline in aging also need investigation.

- Investigate the relationship between daytime and nighttime care procedures and sleep quality and circadian function in the institutionalized elderly. These studies should also investigate modifications of care procedures designed to minimize adverse effects on sleep.