Dreaming & Dementia

New research shows the rapid eye movement stage of sleep may raise the risk of dementia if this phase is insufficiently entered. Often those with dementia have sleep disturbances, but researchers do not know why these sleep troubles occur. Neither is it clear whether different kinds of sleep and sleep phases influence the chances of developing dementia.

A new study was published in the journal Neurology that investigates the rapid eye movement (REM) stage of sleep and whether or not there is a link between REM and dementia incidence. There are 2 stages to sleep; REM and non-REM. The first four stages are all non-REM and the fifth and last sub-phase of sleep is REM and typically occurs after 90 minutes of non-REM sleep. This is when the brain does most of its dreaming.

Dr. Matthew Pase, Ph.D., of the Swinburne University of Technology in Melbourne, Australia is the first author of the new study. He and his team examined data from the large population-based Framingham Heart Study (FHS) that started in 1971.

They examined a subset of FHS participants who had taken part in the sleep study for 3 years between the years 1995 and 1998. They were all at least 60 years old and half were male. The stages of sleep were assessed using a home-based sleep study called polysomnography, which is a widely used approach for assessing sleep phases and disorders.

This test determines sleep cycles and different stages of sleep by recording things such as physiological changes and brain waves. They followed the participants for up to 19 years while looking for cases of dementia. They noted 32 diagnoses of dementia and of those, 24 were Alzheimer’s disease. The participants diagnosed with dementia spent 17% of their entire sleep in REM and those who did not receive a dementia diagnosis spent 20% in REM.

Therefore less REM correlates with dementia risk. Researchers had adjusted for variables such as sex and age and found a strong correlation between higher dementia risk and a lower percentage of REM sleep and longer REM sleep latency. This refers to how long it takes someone to reach the REM phase.

With every percentage point that REM sleep decreased, the researchers found a 9% increase in dementia risk. There were adjustments for possible confounders such as cardiovascular risk factors, depression, and medication. They did exclude those who had mild cognitive impairment and those who developed dementia early in the study.
Possible mechanisms may include stress or anxiety that may curtail REM sleep and increase the risk for dementia or there may be a contributing role of sleep disorders such as sleep-disordered breathing that may disrupt REM sleep and increase the risk for dementia.

Future research should confirm their findings and determine the mechanisms linking REM sleep to incident dementia. The study was small compared to the larger Framingham Heart Study but is still a large sample given that all participants underwent an overnight sleep study and follow-up for dementia. Other sources of similar data are being investigated to possibly combine the analysis and results of such studies.

Dr Fredda Branyon