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Definition: Sundowning from Encyclopedia of Alzheimer's Disease: With Directories of Research, Treatment and Care Facilities

Sundowning is a term used to describe the restlessness and agitation dementia patients experience during the late afternoon or evening hours.

Summary Article: SUNDOWNING
from The Encyclopedia of Elder Care

altered mental state, Alzheimer's disease, circadian rhythm, delirium, dementia, depression, neurocognitive disorder, sensory deprivation, sleep disturbance, sundowning

Alzheimer Disease, Circadian Rhythm, Delirium, Dementia, Depression, Neurocognitive Disorders, Sensory Deprivation, Sleep Wake Disorders

Sundowning (i.e., sundown syndrome) is the term that is used to describe a set of behavioral symptoms associated with neurocognitive disorders common in older adults, which become more evident late in the afternoon, evening, or night. Although sundowning is not included in the Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association [APA], 2013), it is associated with the neurocognitive disorders that are part of the DSM-5. Sundowning occurs in many, but not all, institutionalized and elders with neurocognitive disorders. The name is derived from the time at which the behaviors begin (the afternoon, evening, and nighttime hours) and suggests that persons with delirium, dementia, and other sensory losses are sensitive to reduced light, fatigue, and other environmental changes, that most people accommodate to without difficulty. Sundowning is a clinical phenomenon based on disruptive behaviors, confusion, disorientation, agitation, aggression, pacing, wandering, resistance to redirection, screaming, and yelling. These behaviors may be related to underlying dementia or sleep disturbances. Other clinical features that may be present are mood changes, increased demands, suspiciousness, and visual or auditory hallucinations occurring late in the day.

Associated terms include acute confusion, altered mental state, dementia, and delirium. Delirium is a neuropsychological syndrome characterized by a disturbance of attention and awareness that develops over a short time (APA, 2013). It is an impaired environmental awareness and cognitive change, including altered memory, disorientation, and language disturbance or a perceptual disturbance that cannot be accounted for by preexisting dementia. Delirium is associated with neurochemical or medical etiology. In cases without mental illness, delirium is an emergent condition, and a physical or mental cause should be diagnosed as its etiology (e.g., urinary tract infection, pneumonia, untoward effects of medications and alcohol) and then promptly treated. Delirium also may be associated with sleep–wake disturbances and the altered psychomotor behavior of sundowning. Sleep disturbances are common in people with sundowning. Those with delirium may fall, remove their medical equipment, and vocalize by moaning, cursing, complaining, and screaming and may exhibit aggressive behavior. These behaviors have been found to be associated with a person's expression of physical pain or discomfort and emotional anguish. Nocturnal delirium is referred to as sundown syndrome.


First described in 1941 by Cameron, sundowning has received research and clinical attention, particularly because it is as frustrating for caregivers as it is recurrent and difficult to treat effectively. Sensory deprivation, including visual and hearing impairments and inadequate exposure to light during the day, is associated with confusion and sundowning, Circadian rhythm disturbances related to sundowning include sleep–wake cycle changes in which dreams occur earlier; frequent, sudden awakenings; and increased motor activity at night. Circadian rhythms influence several physiological processes that regulate body functions and behavior. The suprachiasmatic nucleus and melatonin are involved in the pathophysiology of Alzheimer's disease and related dementia and regulate circadian rhythmicity. Melatonin is produced by darkness and sleep. Circadian rhythms are observable in 24-hour-cycle changes in core body temperature, hormonal secretions, red blood cell production, and other physiological processes. Individuals with Alzheimer's disease (AD) are more likely from those without AD to exhibit more activity at night and the later times of peak activity and temperature rhythms associated with sundown syndrome. Sleep disturbances, common in people with all forms of dementia, include sleep apnea, sleep fragmentation, daytime napping, and restless legs syndrome. Medications, such as antidepressants, antipsychotics, hypnotics, benzodiazepines, anticholinergic agents, and analgesics may worsen sundowning.


Differential diagnosis is important when sundown syndrome is suspected. The most probable underlying disorders to be considered are delirium, neurocognitive disorders, and depression. Acute confusion is the term preferred to describe altered cognition and behavior until more definitive diagnoses can be established. The most frequent precipitating factor of any of these altered mental states is medication, especially antidepressants, antipsychotics, narcotics, and other drugs with psychotropic effects.

Differentiating delirium, neurocognitive disorders, and depression is important, and a method for identifying delirium is the confusion assessment method (CAM). The course of delirium fluctuates in 24 hours, whereas depression and dementia have more stable signs and are worse in the morning and during stressful situations. Delirium has a shorter course than either depression or dementia, with global rather than specific attentional disturbances, affect lability that varies from flat to excitable, impaired orientation, and incoherent speech. In depression, the affect is flat, and orientation is normal, with distractible attention and slowed speech. Disturbed sleep is common in both delirium and depression, but the usual pattern of daytime sleep and late wakefulness in depression is a significant indicator. In dementia, the affect is usually stable and may vary from disinhibited to vegetative, with task completion muddled by the inability to plan a sequence of steps, self-monitor, and adapt to cues. The mechanics of speech are normal, although there may be an inability to find or recall words.

As mentioned earlier, delirium is always related to the altered physiological or psychological processes associated with either drug ingestion/withdrawal or general medical conditions. Delirium is caused by diseases of the body systems other than the brain, inflammation, poisons, fluid/electrolyte or acid/base disturbances, and other serious, acute conditions. Peripheral infections such as urinary tract infections or pneumonia are now known to cross the blood–brain barrier, triggering delirium in individuals with preexisting cognitive vulnerabilities. Delirium is embodied by rapid changes such as from lethargy to agitation and from somnolence to euphoria with attention disruption, disorganized thinking, disorientation, and changes in sensation and perception. The multiple etiologies of delirium are described in Delirium.


The most important intervention is accurate and comprehensive assessment and documentation of altered mental states so that a differential diagnosis can be made and appropriate treatment can begin. When sundown syndrome is not related to an underlying medical condition, environmental interventions are appropriate. The patient's physical and social environment should be assessed for zeitgebers, or time providers such as lighting appropriate to the time of day and sleep needs, window shades that may be open or closed, structured meal and activity periods, suitable visitors and visiting hours, and morning and bedtime routines. The caregiver should monitor and modulate noises that are intrusive and use music or other sensory salves to soothe before bedtime. Opportunities for daytime activity and exposure to sunlight should be provided, and access to caffeinated beverages should be limited. Melatonin is available in health food stores and may promote nighttime sleep if administered before bedtime. Of note, melatonin is not approved by the U.S. Food and Drug Administration for safety, effectiveness, or purity. Of special concern are caregivers who need education and support in managing sundowning.

See also Depression Measurement Instruments; Sleep Disorders; Vascular and Lewy Body Dementia.

  • American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). American Psychiatric Publishing Arlington VA.
  • Web Resources
  • ICU Delirium and Cognitive Impairment Study Group:
  • National Guideline Clearinghouse:
  • Society of Critical Care Medicine:,%20Agitation,%20Delirium.pdf.
  • Steven L. Baumann
    © 2017 Springer Publishing Company, LLC

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