Alzheimer’s disease disrupts the brain’s natural sleep-wake cycle, making it hard for people with the condition to sleep well at night and stay awake during the day. This happens because Alzheimer’s damages parts of the brain that control our internal clock, known as the circadian rhythm. The circadian rhythm helps regulate when we feel sleepy and when we feel alert, usually following a roughly 24-hour cycle.
One key brain area involved is the suprachiasmatic nucleus (SCN), which responds to light and other signals to keep our sleep-wake cycle on track. In Alzheimer’s, cells in the SCN become damaged and less active. This damage causes the internal clock to lose its regular rhythm, leading to confusion about when to sleep and when to be awake. As a result, people with Alzheimer’s often sleep too much during the day and struggle to sleep at night.
Another factor is the disruption in the production of melatonin, a hormone that signals the body to prepare for sleep. Alzheimer’s patients often have lower or irregular melatonin levels, which further disturbs their ability to fall asleep and stay asleep. This leads to fragmented sleep, where they wake up frequently during the night, and spend less time in deep sleep and REM sleep—both of which are important for memory and brain health.
Physical changes caused by Alzheimer’s, such as reduced activity levels and less exposure to natural light, also contribute to sleep problems. Less movement and dimmer environments can weaken the cues that help reset the internal clock, worsening the sleep-wake cycle disruption.
These sleep disturbances are not just a side effect; they can make other Alzheimer’s symptoms worse. Poor sleep can increase confusion, restlessness, and wandering, creating a cycle where sleep problems and cognitive symptoms feed into each other.
In some cases, people with Alzheimer’s may also develop sleep disorders like obstructive sleep apnea, which further fragment their sleep and reduce its quality. This is especially seen in certain groups, such as adults with Down syndrome who develop Alzheimer’s, where sleep problems and breathing issues during sleep become more severe as the disease progresses.
Overall, Alzheimer’s disrupts the brain’s sleep-wake cycle by damaging the internal clock mechanisms, altering hormone production, and changing behavior patterns that normally support healthy sleep. This disruption contributes to the sleep difficulties that are common and challenging in Alzheimer’s disease.
