Patients with dementia often develop sleep problems, such as excessive daytime sleepiness and hypersomnolence, in addition to insomnia. In the elderly, the factors that cause insomnia and hypersomnolence are characterized by the overlapping of factors such as symptoms associated with physical disease, stress, psychiatric disease, and drugs. It is thought that the neurodegenerative process in dementia exacerbates the physiological age-related changes, which produces a sleep problem that is difficult to cope with. Furthermore, the frequency of complications of sleep-related disorders, such as sleep apnea syndrome, circadian rhythm sleep disorders, and REM sleep behavior disorder, demonstrates similarities and differences among the causative diseases of dementia. For this reason, how to identify and cope with sleep problems differs depending on the causative diseases of dementia. In recent years, in addition to basic research related to the pathophysiology of dementia, candidate risk factors for dementia have been described in clinical and epidemiological studies. Sleep was suggested to be involved in the maintenance of cognitive function and excretion of brain accumulations as a physiological role, and that sleep problems can affect dementia symptoms and the neurodegenerative process of dementia. Intervention studies, such as sleep deprivation in animals and humans, revealed an association between sleep deprivation/insomnia and dementia. On the other hand, observational studies examined the relationship between excessive daytime sleepiness and prolonged sleep time and the risk of developing dementia. As an intervention for sleepiness or hypersomnolence in dementia, it is important to comprehensively evaluate and cope with sleep hygiene, the direct causes of sleep problems, and comorbid sleep-related disorders.
 Author's abstract