Study expands the science on the link between sleep and dementia

By Kristen Rogers, CNN

(CNN) — If you find yourself sleepy during your daily activities in your older age, you may need to consider it more than an inconvenience — since the fatigue may indicate you’re at higher risk for developing a condition that can lead to dementia, a new study has found.

Among participants who experienced excessive daytime sleepiness and a lack of enthusiasm, 35.5% developed motoric cognitive risk syndrome compared with 6.7% of people without those problems, according to the study published Wednesday in the journal Neurology.

Motoric cognitive risk syndrome, or MCR, is marked by slow walking speed and complaints of memory problems among older people who don’t already have dementia or a mobility disability. The risk of developing dementia more than doubles in those with this syndrome, which was first described in 2013.

“Previous studies have shown a link between sleep disorders and the risk of dementia,” said first study author Dr. Victoire Leroy, assistant professor of geriatric medicine at Tours University Hospital in France, via email.

But some of those scientific reports examined that link largely at only one point in time, according to the study. Not much has been known about the relationship between certain aspects of poor-quality sleep and pre-dementia syndromes, either, Leroy and the research team wrote — so they wanted to expand the research in this field.

“Establishing the relationship between sleep dysfunction and MCR risk is important because early intervention may offer the best hope for preventing dementia,” the authors said.

Tracking sleep patterns

The findings are based on 445 adults who were age 76 on average and recruited from New York’s Westchester County for the Central Control of Mobility and Aging study, which assesses the cognitive processes and brain mechanisms that regulate mobility in aging. Participants walked on treadmills so their initial gaits could be recorded, then were assessed annually from 2011 to 2018.

The study authors also collected yearly data on participants’ recollections of their sleep quality and quantity in the two weeks leading up to the assessments. Specifically, the team gleaned details within seven components of the Pittsburgh Sleep Quality Index: subjective sleep quality, time it takes to fall asleep, sleep duration, sleep efficiency (ratio of total hours asleep to total hours in bed), sleep disturbances, use of sleep-inducing medication, and daytime dysfunction, such as having trouble staying awake during activities or feeling less enthusiasm to get things done.

Over a follow-up period of roughly three years on average, 36 participants developed motoric cognitive risk syndrome. Compared with “good” sleepers, “poor” sleepers had only a slightly higher risk of MCR. But when the authors considered the seven sleep components separately, only daytime dysfunction was associated with 3.3 times higher risk of MCR.

The study findings may help physicians and patients be more open to asking questions about sleep patterns, and to looking more closely at walking speed when making an early diagnosis, said Dr. Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Florida. Richardson wasn’t involved in the study.

Sleep’s link to brain decline

The study has a few “serious” limitations, said Dr. Tara Spires-Jones, professor of neurodegeneration and director of the Centre for Discovery Brain Sciences at the University of Edinburgh in Scotland, via email.

“The sleep measurements were self-reported, not measured by a scientist, and these self-reports could be biased by people with memory issues,” said Spires-Jones, who wasn’t involved in the study. “The participants in the study were also largely white, and the group was much smaller than similar single-timepoint studies, so the results will be stronger if confirmed in future studies.”

The authors acknowledged that while the length of their study, at roughly three years, is longer than that of some previous research, the follow-up period is still short.

Motoric cognitive risk syndrome is newly identified, so experts still have a lot to learn before they can explain in detail what causes it and how it affects the body, Isaacson said. This is complicated by the lack of “definitive pathological biomarkers” for MCR thus far, Isaacson said.

But “several mechanisms might explain this association,” Leroy said. “Sleep plays a role in ‘cleaning up’ neurotoxins accumulated in the brain. In addition, previous studies have shown a greater accumulation of proteins associated with Alzheimer’s disease in sleep-deprived individuals.

“One possible alternative or additive way is through the activation of brain inflammatory response, which is observed in Alzheimer’s disease and related dementias,” Leroy said.

It’s unclear why out of seven sleep components, daytime dysfunction was the only one significantly associated with MCR risk, when one might think that the other six components — which included sleep quality and quantity — would play a role in daytime dysfunction, experts said.

Spires-Jones pointed out that for the potential link between daytime dysfunction and MCR, reverse causation is also possible.

“Scientific evidence is suggesting that when you are in the early stages of dementia, pathological changes in the brain disrupt sleep,” she added — meaning it’s “likely the early disease causing sleep disruption, not disruption causing disease.”

It’s well known that sleep disturbances such as REM sleep behavior disorder can be early predictors of conditions including Lewy body dementia or Parkinson’s disease, Isaacson said.

Monitoring sleep health in aging

The study results show how precious sleep is, Leroy said.

People having trouble with their sleep should talk to their doctors, consider completing a sleep questionnaire, and discuss whether an at-home or in-hospital sleep study may be helpful, Isaacson said.

“There are now many treatments, both drug and non-drug approaches, that may be able to help depending on the exact problem found,” he added. “Treating sleep disturbances should pay dividends for many years, even decades, on overall brain health and dementia prevention.”

You can take other measures to protect your brain during aging.

“Living a healthy lifestyle including eating well, maintaining a healthy weight, keeping your body and brain active, and treating any hearing loss are all ways of boosting brain resilience and likely lowering dementia risk,” Spires-Jones said.

“This is not to blame people who have dementia for their lifestyle choices,” she added. “Best estimates indicate that less than half of the risk of dementia is due to this type of modifiable risk factor with the rest of the risk likely due to genes we inherit.”

However, given the potential to modify your risk and the growth of medical research and treatments, Spires-Jones added, there is reason to be hopeful.

If you’re already experiencing mobility issues, fall prevention can help, Isaacson said — that can include physical and occupational therapy evaluation, and at-home adaptations such as installing bars in the shower, removing clutter and using night-lights.

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