According to new research, the rapid eye movement stage of sleep – which is when most of our dreaming occurs – may raise the risk of dementia if this phase is insufficiently entered. Share on Pinterest Researchers say lack of REM sleep may raise the risk of dementia. It is known that people with dementia often have sleep disturbances. However, researchers do not yet know why these sleep troubles occur, nor is it clear whether different kinds of sleep and sleep phases influence the chances of developing dementia. A new study – published in the journal Neurology – investigates the rapid eye movement (REM) stage of sleep and whether or not there is a link between REM and dementia incidence. Put simply, sleep occurs in two large stages: REM and non-REM. In more detail, the first four stages are all non-REM. The fifth and last sub-phase of sleep, REM, typically occurs after 90 minutes of non-REM sleep, and this is when the brain does most of its dreaming. The first author of the new study is Matthew Pase, Ph.D., of the Swinburne University of Technology in Melbourne, Australia. Dr. Pase and team examined data from the large population-based Framingham Heart Study (FHS), which started in 1971.

Studying REM sleep and dementia risk Dr. Pase and colleagues examined a subset of FHS participants who had taken part in the Sleep Heart Health Study for 3 years between 1995 and 1998. At the time of that study, the participants were at least 60 years old and half of them were male. Sleep stages were assessed using a home-based sleep study, or polysomnography, which is a widely used approach for assessing sleep phases and disorders. The test can determine sleep cycles and different stages of sleep, such as REM or non-REM, by recording things such as physiological changes and brain waves. The team followed up the participants for up to 19 years, all the while looking for cases of dementia. During the follow-up period, Dr. Pase and colleagues noted 32 diagnoses of dementia, 24 of which were Alzheimer’s disease. Those who developed dementia spent 17 percent of their entire sleep in REM, on average, whereas those who did not receive a dementia diagnosis spent 20 percent, on average, in REM.

Less REM correlates with dementia risk The researchers adjusted for variables such as sex and age, and they found a strong correlation between higher dementia risk and a lower percentage of REM sleep and longer “REM sleep latency,” which refers to how long it takes someone to reach the REM phase. Specifically, with every percentage point that REM sleep decreased, the researchers found a 9 percent increase in dementia risk. The correlation withstood adjustments for possible confounders such as cardiovascular risk factors, depression, and medication. Dr. Pase and team excluded from their analysis those who had mild cognitive impairment – an early marker of Alzheimer’s – at baseline, as well as those who developed dementia early in the study. He spoke to Medical News Today about the significance of the findings. “In our study, the association between lower REM sleep and dementia was not explained by those with cognitive impairment at baseline or by those who converted to dementia within the first 3 years, [which] suggests that reduced REM is not simply a consequence of early dementia.” Matthew Pase, Ph.D. Speaking to MNT about the possible mechanisms that could explain the findings, he said, “We do not have the exact answers but we have a few hypotheses.” “Possible mechanisms may include (i) stress or anxiety, which may curtail REM sleep and increase risk for dementia, (ii) there may be a contributing role of sleep disorders such as sleep-disordered breathing, which may disrupt REM sleep and increase risk for dementia, and (iii) more REM sleep may help maintain brain integrity in the face of changes that occur with aging and early Alzheimer’s disease.”