International Journal of Molecular Medical Science, 2025, Vol.15, No.4, 155-164 http://medscipublisher.com/index.php/ijmms 156 becomes more broken, and waking up at night is common. These changes are stronger than in healthy older people, showing the effect of brain degeneration on areas that control sleep (Wennberg et al., 2017; Mou et al., 2024). Problems with the body clock are also frequent, with irregular sleep-wake times, weaker daily rhythms, and sometimes a flipped day-night schedule. These clock problems relate to dementia progression and the damage in key clock centers, including the suprachiasmatic nucleus and other time- keeping systems (Okawa et al., 1991; Bombois et al., 2010). These sleep and clock problems are not only effects of dementia; they may also help trigger it and speed it up. Studies suggest that insomnia and sleep- disordered breathing raise the chance of later dementia, pointing to a two- way link between sleep and thinking decline (Shi et al., 2017; Wennberg et al., 2017; Kitamura et al., 2020; Ferini-Strambi, 2022). Therefore, finding and treating these issues is important for both prevention and day- to- day care in the elderly. 2.2 Major clinical manifestations and commonly used assessment methods for sleep disorders Many older people with dementia have sleep problems, including insomnia, feeling sleepy in the day, breathing trouble during sleep (such as obstructive sleep apnea), restless legs, and REM sleep behavior disorder. In daily life, this may show up as taking a long time to fall asleep, waking often at night, wandering, becoming restless or upset, and taking extra daytime naps (Porter et al., 2015; Wennberg et al., 2017). Of these issues, insomnia and sleep apnea are the most commonly diagnosed (Bombois et al., 2010; Tallavajhula, 2024). Sleep problems are examined through what people say and device detection. Questionnaires filled out by patients or caregivers are widely used, but they may not notice the severity of the problem. More accurate data can be collected through activity recorders and polysomnography recorders, which can observe sleep efficiency, the duration of sleep, and how sleep is interrupted. It is recommended to conduct a comprehensive inspection using these tools (Okawa et al., 1991; Bombois et al., 2010). It is important to detect problems early because sleep problems are often overlooked in daily care (Higami et al., 2022). 2.3 Negative effects of sleep disorders on cognition, mood, and daily functioning In dementia, sleep problems are tied to faster decline in thinking, including worse memory, attention, and executive skills. Poor sleep can also make mood and behavior symptoms worse-such as depression, irritability, and confusion-lowering quality of life (Vitiello and Borson, 2001). Beyond thinking, sleep troubles raise the chance of agitation and wandering, which can cause injuries and add to caregiver load (Bombois et al., 2010; Porter et al., 2015; Wennberg et al., 2017). Daily life is also affected: people have more trouble with basic tasks and keeping independence. Long- lasting sleep problems increase caregiver stress and are a major reason for moving patients into institutions (Vitiello and Borson, 2001; Bombois et al., 2010; Porter et al., 2015). Tackling sleep issues is thus key to protecting both cognitive and functional abilities and to improving overall well- being in this vulnerable group. 3 Physiological Roles and Pathological Changes of Melatonin and Cortisol 3.1 Melatonin secretion rhythm, regulatory mechanisms, and declining trends in dementia Melatonin is a hormone mainly made by the pineal gland, and its release is strongly guided by the light–dark cycle. In normal cases, melatonin rises in the evening, peaks at night, and drops in the early morning, helping set daily rhythms and supporting falling asleep and staying asleep (Nous et al., 2021; Zhang, 2024). This daily pattern is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus, which reads light signals from the environment to match melatonin timing with the sleep-wake cycle (Lin et al., 2013). In dementia, especially Alzheimer’s disease, both the size and regularity of the melatonin rhythm are clearly reduced. Night- time melatonin is lower than in same- age healthy people, and the circadian pattern looks flattened or disrupted (Dori et al., 1994). This drop relates to aging and the degree of brain degeneration, and it contributes to the common sleep and body- clock problems seen in dementia (Lin et al., 2013; Ferrari et al., 2000; Nous et al., 2021).
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