Dementia and Sleep Dysfunction: Tips for Practice

Richard S. Isaacson, MD


June 26, 2017

I'm Richard Isaacson, director of the Alzheimer's Prevention Clinic at Weill Cornell Medicine in New York-Presbyterian. A new study recently published in Neurology looked at the quantity of a person's sleep and how that could correlate with the diagnosis of dementia later in life. The study was very interesting. It may not have found what you would think. Patients who were 65 years old and older who slept more than 9 hours per night were at greater risk of developing Alzheimer disease.[1] However, the devil is sometimes in the details.

If you look at the study, in patients who slept longer, this may actually be a premonitory symptom of dementia and Alzheimer disease itself. Impaired sleep-wake cycle is something we see in clinical practice. Impaired sleep or prolonged sleep greater than 9 hours: Is that a risk factor for Alzheimer disease, or is that actually a part of the disease? I would say the latter. Impaired or prolonged sleep is one of the earliest signs that something may be wrong when it comes to a neurodegenerative dementia.

In your clinical practice, it is helpful to ask: Was there a change in sleep pattern? Also in the study was another very interesting finding: People who slept longer than 9 hours a night who also had less than a high school education were at a 600% increased risk for dementia.[1] Now, that underscores a couple of things: When you have higher educational status, the theory of cognitive reserve or a cognitive backup system can certainly protect against dementia. In this case, when you combine the two factors in this study, there was a profound increase in the likelihood that that person will be diagnosed with dementia later.

What are the take-home points of the study? Number one, take a sleep history. As part of any risk factor assessment, either for trying to reduce a person's risk for Alzheimer disease or when you're first trying to make a diagnosis of a person with cognitive impairment, does that person have mild cognitive impairment due to Alzheimer disease? Could it be even a pseudo dementia of depression? Could it be a metabolic or vitamin deficiency? Doing an adequate sleep history may give you a little bit of a clue. That being said, sleeping longer also is found with patients who have depression. Screening for depression is really key.

When it comes to clinical practice, some of the most important considerations include the duration of sleep and whether the sleep pattern or sleep duration changed over time. The other consideration is: What is the quality of the sleep? For example, in our practice, we have a subset of patients who like to wear a tracking band. This is a biosensor band that looks at overall duration of sleep and tries to give the best estimation based upon a variety of measures of pulse rate, temperature, movements, and heart rate variability. A tracking band like this cannot only say how many hours a person has slept for but maybe how many hours that person was in REM sleep, how many hours that person was in slow wave or deep sleep, and how many times that person was awake.

This is a very interesting piece of data because when you're treating a person for insomnia, well, that is one thing. You can try to get them to fall asleep more quickly. If you're treating someone for a sleep disturbance, and they wake up in the middle of the night, that may be a different intervention. In Alzheimer disease, there is also a lot of correlation between Alzheimer disease and sleep patterns.[2]

As an example, during the day when a person is engaged in their everyday activities and remembering things, those memories experienced during the day are consolidated during REM sleep. If a person is not having adequate REM sleep, their cognitive function the next day may be impaired. However, if a person is not having adequate amounts of slow wave sleep or deep sleep—the time during which a person's amyloid is disposed of—that can lead to [more amyloid in the brain]. You have heard about the lymphatic system, but there is a newly discovered disposal system for the brain called the glymphatic system. This is how the "trash"—or the amyloid—gets taken out; and if you're not having enough slow wave sleep, maybe you can't take out the "trash" and dispose of that amyloid.[2]

I think the field of sleep medicine in Alzheimer disease is fascinating. Whether it's through clinical observation or historical fact, there's a great deal of really interesting information when it comes to sleep and Alzheimer disease. Hopefully, as further studies come out, we'll be able to implement the things that we learn in our clinical practice. Thank you.


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