A person may sleep through the night believing they barely woke at all, while the brain experiences many tiny interruptions.
New research suggests these brief awakenings could be connected with inherited vulnerability to Alzheimer’s disease during middle age. The University of Liège study was published in the journal Sleep.
Researchers examined sleep in more than 500 healthy people who had no signs of dementia. They discovered that among participants aged 50 to 69, those with a higher genetic risk of Alzheimer’s tended to have more brief awakenings during sleep. This connection did not appear in the younger group, whose members were mainly between 18 and 31.
The finding matters because Alzheimer’s does not suddenly begin when someone becomes forgetful. Changes associated with the disease can develop quietly in the brain for many years before diagnosis. Scientists hope that finding reliable early markers could eventually create more time for prevention or treatment.
Alzheimer’s disease slowly damages brain cells and is the most common form of dementia. Memory loss is one of its best-known symptoms, but later stages can also affect language, judgment, behavior and the ability to carry out ordinary tasks. Age is the strongest risk factor, although genes also influence susceptibility.
Alzheimer’s is not usually inherited in a simple way from one parent. Instead, many small genetic differences can raise or lower risk. Researchers can combine some of these differences into what is called a polygenic risk score.
The Liège team calculated this type of score for each participant and then looked for links with sleep. The score cannot diagnose Alzheimer’s or tell a healthy person that they will eventually develop dementia. It is mainly a research tool that estimates inherited risk across groups of people.
The strongest sleep connection involved micro-awakenings. These are extremely brief shifts toward being awake that may occur without a sleeper remembering them. A few interruptions are normal, but frequent ones can break sleep into smaller pieces.
Among the middle-aged and older adults in the study, more micro-awakenings were associated with higher genetic risk. The absence of the same pattern in young adults raises the possibility that the relationship between sleep and Alzheimer’s vulnerability changes with age. It does not establish when Alzheimer’s begins or prove that poor sleep triggers the disease.
One possible biological connection lies in a tiny area of the brainstem called the locus coeruleus. This region helps the brain control alertness, attention and sleep. It is only very small, but scientists increasingly suspect it may have an important role in the earliest stages of Alzheimer’s-related changes.
The region is especially interesting because abnormal tau protein can begin accumulating there surprisingly early. In a healthy brain, tau supports the internal structure of nerve cells. In Alzheimer’s disease, abnormal tau builds up and is associated with damage to brain cells.
The University of Liège team has studied the locus coeruleus using a powerful 7-Tesla MRI scanner. Earlier research found links between the condition of this brain region and several aspects of sleep, including how quickly people fall asleep and the depth of their sleep. Its functioning was also associated with REM sleep quality.
REM is the sleep stage in which vivid dreaming commonly occurs. The brain is highly active during this period, and REM sleep is involved in memory and other important brain functions. Disturbances across different sleep stages may therefore give scientists information about systems that are also affected by aging and brain disease.
The long-term hope is that sleep could become an affordable and accessible source of information about brain health. Researchers might eventually combine sleep measurements with genetic information, blood tests, brain imaging or memory testing to identify people who deserve closer monitoring. Scientists are also asking whether treating sleep problems could reduce future risk.
That possibility is appealing because sleep can sometimes be improved through changes in behavior or treatment of conditions such as sleep apnea. But the current research does not show that improving sleep prevents Alzheimer’s disease. Clinical studies would be needed before sleep treatment could be recommended specifically as an Alzheimer’s prevention strategy.
The study has several useful features, including the examination of people before symptoms appeared and the comparison of two very different age groups. It also connects sleep research with genetic risk and previous brain-imaging work. These different approaches provide researchers with several ways to investigate the same biological question.
At the same time, the results need cautious interpretation. An association does not show that one factor causes another, and micro-awakenings can occur for many reasons unrelated to Alzheimer’s disease. The study also cannot use a person’s sleep pattern to predict with confidence whether that individual will develop dementia.
Long-term studies that follow healthy participants for many years will be particularly important. Researchers need to learn whether people with both higher genetic risk and disrupted sleep are actually more likely to develop Alzheimer’s changes later. They will also need to test whether the findings appear in larger and more diverse populations.
For now, waking briefly during the night should not be treated as an early diagnosis of Alzheimer’s disease. The more important scientific message is that sleep may reflect subtle changes in brain systems long before memory loss becomes visible. If that connection is confirmed, the sleeping brain could eventually help researchers identify vulnerability at a much earlier stage.
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Source: University of Liège.
