Hit the sleep `sweet spot' to keep brain sharp
Too little and too much sleep linked to cognitive decline

Date:
October 20, 2021
Source:
Washington University School of Medicine
Summary:
Older adults who sleep short or long experienced greater cognitive
decline than those who sleep a moderate amount, even when the
effects of early Alzheimer's disease were taken into account,
according to a new study.



FULL STORY ==========================================================================
Like so many other good things in life, sleep is best in moderation. A multiyear study of older adults found that both short and long sleepers experienced greater cognitive decline than people who slept a moderate
amount, even when the effects of early Alzheimer's disease were taken
into account. The study was led by researchers at Washington University
School of Medicine in St.

Louis.


==========================================================================
Poor sleep and Alzheimer's disease are both associated with cognitive
decline, and separating out the effects of each has proven challenging. By tracking cognitive function in a large group of older adults over several
years and analyzing it against levels of Alzheimer's-related proteins
and measures of brain activity during sleep, the researchers generated
crucial data that help untangle the complicated relationship among sleep, Alzheimer's and cognitive function. The findings could aid efforts to
help keep people's minds sharp as they age.

The findings are published Oct. 20 in the journal Brain.

"It's been challenging to determine how sleep and different stages of Alzheimer's disease are related, but that's what you need to know to
start designing interventions," said first author Brendan Lucey, MD, an associate professor of neurology and director of the Washington University Sleep Medicine Center. "Our study suggests that there is a middle range,
or 'sweet spot,' for total sleep time where cognitive performance was
stable over time. Short and long sleep times were associated with worse cognitive performance, perhaps due to insufficient sleep or poor sleep
quality. An unanswered question is if we can intervene to improve sleep,
such as increasing sleep time for short sleepers by an hour or so, would
that have a positive effect on their cognitive performance so they no
longer decline? We need more longitudinal data to answer this question." Alzheimer's is the main cause of cognitive decline in older adults, contributing to about 70% of dementia cases. Poor sleep is a common
symptom of the disease and a driving force that can accelerate the
disease's progression.

Studies have shown that self-reported short and long sleepers are both
more likely to perform poorly on cognitive tests, but such sleep studies typically do not include assessments of Alzheimer's disease.

To tease apart the separate effects of sleep and Alzheimer's disease on cognition, Lucey and colleagues turned to volunteers who participate
in Alzheimer's studies through the university's Charles F. and Joanne
Knight Alzheimer Disease Research Center. Such volunteers undergo annual clinical and cognitive assessments, and provide a blood sample to be
tested for the high- risk Alzheimer's genetic variant APOE4. For this
study, the participants also provided samples of cerebrospinal fluid
to measure levels of Alzheimer's proteins, and each slept with a tiny electroencephalogram (EEG) monitor strapped to their foreheads for four
to six nights to measure brain activity during sleep.

In total, the researchers obtained sleep and Alzheimer's data on 100 participants whose cognitive function had been monitored for an average
of 4 1/ 2 years. Most (88) had no cognitive impairments, 11 were very
mildly impaired, and one had mild cognitive impairment. The average age
was 75 at the time of the sleep study.

The researchers found a U-shaped relationship between sleep and cognitive decline. Overall, cognitive scores declined for the groups that slept
less than 4.5 or more than 6.5 hours per night -- as measured by EEG --
while scores stayed stable for those in the middle of the range. EEG
tends to yield estimates of sleep time that are about an hour shorter
than self-reported sleep time, so the findings correspond to 5.5 to 7.5
hours of self-reported sleep, Lucey said.

The U-shaped relationship held true for measures of specific sleep phases, including rapid-eye movement (REM), or dreaming, sleep; and non-REM sleep.

Moreover, the relationship held even after adjusting for factors that can affect both sleep and cognition, such as age, sex, levels of Alzheimer's proteins, and the presence of APOE4.

"It was particularly interesting to see that not only those with short
amounts of sleep but also those with long amounts of sleep had more
cognitive decline," said co-senior author David Holtzman, MD, a professor
of neurology. "It suggests that sleep quality may be key, as opposed to
simply total sleep." Each person's sleep needs are unique, and people
who wake up feeling rested on short or long sleep schedules should not
feel compelled to change their habits, Lucey said. But those who are not sleeping well should be aware that sleep problems often can be treated.

"I ask many of my patients, 'How's your sleep?'" said co-senior author
Beau M.

Ances, MD, PhD, the Daniel J. Brennan, MD, Professor of Neurology. Ances
treats patients with dementia and other neurodegenerative conditions
at Barnes-Jewish Hospital. "Often patients report that they're not
sleeping well. Often once their sleep issues are treated, they may have improvements in cognition.

Physicians who are seeing patients with cognitive
complaints should ask them about their quality
of sleep. This is potentially a modifiable factor." ========================================================================== Story Source: Materials provided by
Washington_University_School_of_Medicine. Original written by Tamara
Bhandari. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Brendan P Lucey, Julie Wisch, Anna H Boerwinkle, Eric C Landsness,
Cristina D Toedebusch, Jennifer S Mcleland, Omar H Butt, Jason
Hassenstab, John C Morris, Beau M Ances, David M Holtzman. Sleep
and longitudinal cognitive performance in preclinical and
early symptomatic Alzheimer's disease. Brain, 2021 DOI:
10.1093/brain/awab272 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211020135920.htm

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