Researchers have long known that people with dementia often experience disturbed sleep, but it has been unclear if sleep disruption is a consequence of the disease or if it is associated with the risk of dementia. Now, using data from the Framingham Heart Study (FHS), Matthew P. Pase, a fellow in the department of neurology at the Boston University School of Medicine (MED), and a team of MED researchers have found that people who experience less rapid eye movement (REM) sleep and take longer to reach the REM sleep stage may have a greater risk of developing dementia.
“We set out to discover which stages of sleep may be linked to dementia, and while we did not find a link with deep sleep, we did with REM sleep,” says Pase, an FHS investigator and the co-author of the study, which was published in the August 23, 2017, online issue of Neurology, the medical journal of the American Academy of Neurology. He presented his findings in July 2017 at the Alzheimer’s Association International Conference in London.
Pase’s team included co-author Jayandra J. Himali, a MED research assistant professor in the department of neurology who holds a joint appointment at the BU School of Public Health, and Sudha Seshadri, a MED professor of neurology, an FHS investigator, and a faculty member at BU’s Alzheimer’s Disease Center.
The team looked at 321 people over the age of 60—their average age was 67—whose sleep cycles were measured during an overnight sleep study between 1995 and 1998. Researchers followed the participants for an average of 12 years. During that period, 32 people were diagnosed with some form of dementia; of those, 24 were found to have Alzheimer’s disease.
Those who developed dementia spent an average of 17 percent of their sleep time in REM sleep; that figure was 20 percent for those who did not develop dementia. After adjusting for age and sex, researchers found that for every percent that REM sleep was reduced, there was a nine percent increase in the risk for all forms of dementia and an eight percent increase in the risk of dementia due to Alzheimer’s disease. The researchers came up with similar results after adjusting for other factors that could affect dementia risk or sleep, such as heart disease, depression symptoms, and medication use. They did not find an association between other stages of sleep and an increased risk for dementia.
“Different stages of sleep may differentially affect key features of Alzheimer’s disease,” says Pase. “Our findings implicate REM sleep mechanisms as predictors of dementia. The next step will be to determine which mechanisms of REM sleep lead to the greater risk of dementia. By clarifying the role of sleep in the onset of dementia, the hope is to eventually identify possible ways to intervene so that dementia can be delayed or even prevented.”
The researchers note that the limitations of the study include its small sample size and, because all the participants were of Caucasian descent, it is unclear how the results would apply to other ethnic groups. The study was supported by the National Heart, Lung, and Blood Institute, the National Institute on Aging, and the National Institute of Neurological Disorders and Stroke.
Earlier in 2017, Pase and Seshadri were co-authors of a study that found that older adults who began getting more than nine hours of sleep a night—but had not slept that much in the past—had double the risk of developing all forms of dementia, including Alzheimer’s, a decade later than those who slept nine hours or less. Those findings, which were based on FHS data, were reported in the journal Neurology.