Ask the BCAT Faculty: Does Lack of Sleep Lead to Dementia?
I recently heard Dr. Mansbach talk at a conference about healthy habits to reduce the risk of developing dementia. He mentioned chronic poor sleep as a potential risk factor, but not one of the six main ones. Can the BCAT faculty share information about the possible relationship between sleep and dementia? There seems to be a lot of talk about it.
St Louis, MO
Thank you for your question, Harold. There is not only a lot of conversation about the relationship between sleep and dementia, but also a growing body of research devoted to the exploration of the nature of the relationship between the two. The hypothesis that the two are linked is based on the observation that people with dementia tend to experience a disruption in the "internal body clock." When this occurs, the sleep cycle is inverted such that there is an increase in night-time wakefulness and daytime somnolence. The correlation between sleep disturbances and dementia is well-documented, but causality and directionality are uncertain. Researchers have begun to explore the possibility that not only can dementia contribute to sleep disturbances, but also chronic poor sleep may contribute to the development of dementia. So what does the science tell us?
As the body sleeps, the brain consolidates memories and performs certain ‘housekeeping’ tasks. During deep or “slow wave” sleep, the neuropathways between the hippocampus and the neocortex are reactivated. It is thought that this process further consolidates memories, “cementing” them in place. This second consolidation phase increases the likelihood that memories will be recalled hours or years later. This may explain why it is hard to recall information the day after a very poor night of sleep. Fitful sleep or an insufficient amount of sleep prevents the body from going into the slow wave stage in which reactivation occurs. In addition to allowing memories to be “cemented,” there is some evidence that deep sleep allows the brain to rid itself of neurotoxins and proteins that can compromise cognitive functioning. One of these neurotoxins appears to be the protein beta-amyloid, which is strongly implicated in the development of Alzheimer’s disease.
A number of animal studies have demonstrated an association between chronic poor sleep and beta-amyloid build-up in the brain. Recently, researchers at UC Berkeley applied the animal study findings to humans. They found that among human participants who did not have dementia, those who experienced the worst sleep had the highest concentrations of beta-amyloid and performed the worst in a memory learning task. Of course, this does not necessarily mean that poor sleep causes a build-up of beta-amyloid, or that beta-amyloid causes problems in memory. The direction of the association could be reversed. In other words, beta-amyloid build-up could cause poor sleep. Another possibility is that a third health variable, such as pain, diabetes, or cardiovascular disease, contributes to both poor sleep and the development of dementia.
The nature of the association between sleep and dementia is uncertain. There is also ambiguity surrounding what constitutes the “right” amount of sleep. It may vary from person to person. One thing that is certain across the board is that sleep plays a vital role in maintaining positive physical and psychological health. Though it has yet to be established that chronic poor sleep necessarily contributes to the development of dementia, there is strong evidence that physical exercise, cognitive stimulation, no smoking, positive mood, healthy heart, and healthy weight may reduce the risk of dementia. Interestingly, these six habits may also improve your sleep!
In future posts we will be talking more about ways to lower risk of dementia.