For every percentage of REM sleep loss, the risks of dementia increased 9%.
Less time in the rapid eye movement (REM) stage of sleep considerably increases risk of dementia, possibly due to sleep-disordered breathing, according to new research.
The study, led by Matthew Pase (pictured), PhD, senior research fellow at Swinburne University in Australia, examined 32 cases of incident dementia, 24 of which were consistent with dementia related to Alzheimer disease.
“Our first thought was that REM was a marker for the early stages for dementia, but what we’re seeing is that 18 years in the future, REM is associated with a risk of it,” Pase told MD Magazine. “One theory is that higher REM sleep helps preserve brain integrity and function, working in a protective fashion. The other would be that there is something that is causing a lower REM cycle and also causing dementia, which could be something psychologic, such as stress or anxiety.”
Sampling 321 Framingham Heart Study (FHS) Offspring participants that had participated in the 1995 to 1998 Sleep Heart Healthy Study, the study quantified stages of sleep with home-based polysomnography. The average participant age was 67, with participants being 50% male and 50% female. The study had a mean follow-up of 12 years.
The average individual spends roughly 20% of their total time sleeping in the REM sleep stage as they progress through the 5-stage sleep cycle. The researchers investigated the amount of time spent in stage 1, stage 2, slow-wave sleep (stage 3 and 4 combined), and REM sleep.
For each percentage reduction in REM sleep, a 9% increase in the risk of incident dementia was found. Overall, after adjusting for age and gender, lower percentages of REM sleep were found to be associated with all-cause dementia (HR 0.91; 95% CI 0.86, 0.97; p = 0.004) and for Alzheimer’s dementia (HR 0.92; 95% CI 0.86, 0.99; p = 0.02).
Following adjustments made for multiple covariates — including vascular risk factors, depressive symptoms, and medication use – the magnitude of the association between REM percentage and dementia remained similar.
When the researchers excluded cases of mild cognitive impairment and dementia developed within 3 years of follow-up, the association still remained similar.
However, the Pase noted that REM sleep can be disrupted by an untreated sleep disorder, finding that the association between REM sleep and dementia could be partially explained by hypopneas. When participants with hypopnea were excluded, the association was reduced (HR 0.94), but not significantly (p = 0.17).
“Despite contemporary interest in slow-wave sleep and dementia pathology, our findings implicate REM sleep mechanisms as predictors of clinical dementia,” the authors noted.
“It’s too early to make clinical recommendations, especially since measuring REM sleep involves taking an overnight measurement,” Pase said. “But, sleep disorders appear to be associated with increased risk of dementia, so doctors should be advised to screen for them.”
Going forward, Pase mentioned that further study would be needed, stating that it could be possible to combine the data with other large cohorts or to examine subclinical outcomes, such as REM’s association with declined cognitive function.
“The emerging picture is that REM sleep is related and important to dementia,” he said. “Why that is, is what we’re trying to work out.”
The study, “Sleep architecture and the risk of incident dementia in the community,” was published online in Neurology.