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AMSTERDAM -- Better sleep consolidation and the absence of sleep apnea were associated with better global cognition over 5 years, a pooled analysis of sleep studies in nearly 6,000 adults showed.

Across five cohorts, higher sleep maintenance efficiency (pooled β per 1% increase 0.08, P<0.01) and lower wake after sleep onset (pooled β per 1-min increase -0.07, P=0.02) were associated with better global cognition, reported Matthew Pase, PhD, of Monash University in Melbourne, Australia, at the Alzheimer's Association International Conference. Results were also published in .

An apnea-hypopnea index (AHI) score of 5 or more, indicating mild to severe obstructive sleep apnea, was associated with poorer global cognition (pooled β -0.06, P=0.01) compared with an AHI less than 5. Comparable results were found for moderate to severe apnea. Sleep stage percentages were not associated with global cognition across cohorts.

Prior research has shown a bidirectional relationship between dementia and sleep that may span decades.

"Most of our knowledge on sleep, cognition, and dementia relationships comes from studies using subjective sleep or analysis of activity patterns using actigraphy," Pase said. "We used in-home, gold-standard sleep studies to clarify the aspects of sleep that are most strongly related to cognitive function in almost 6,000 persons."

"The significance of mild asymptomatic sleep apnea has previously been unclear as studies tend to examine participants who have presented with sleep complaints," Pase pointed out. "Since participants in this community-based study did not present with any specific sleep complaints, the association between even mild obstructive sleep apnea and poorer cognition is an important observation."

"Approximately half our sample had evidence of at least mild obstructive sleep apnea," he added. "Treatment trials are needed to determine whether sleep treatment can mitigate cognitive decline."

Pace and colleagues curated data from the newly created Sleep and Dementia Consortium, incorporating information from five U.S. population-based cohorts: the study, the , the , the , and the .

The inaugural analysis included 5,946 participants with no history of stroke or dementia who underwent overnight, home-based type II polysomnography (PSG) and neuropsychological assessments over 5 years of follow-up. Results were adjusted for demographic variables, time between PSG and neuropsychological testing, BMI, antidepressant use, and sedative use.

"The use of five pooled independent community cohorts enabled us to draw robust conclusions, as compared to any single study alone," Pase said.

Across cohorts, 31.5% of participants were women, and mean ages ranged from 58 to 89 at the time of PSG. The median wake after sleep onset time ranged from 44 to 101 minutes, and the prevalence of moderate to severe apnea ranged from 17% to 29%.

The percentage of people with at least mild obstructive sleep apnea ranged from 45% to 64%, reflecting differences in age and sex of the cohorts, Pase noted.

Pooled estimates showed short total sleep time was associated with poorer attention and processing speed. Pooled effects did not show overall associations between sleep and learning and memory or visuospatial abilities.

A limitation of the study was that sleep and cognition were assessed at one time point. Given that associations between sleep and brain health are likely bidirectional, longer follow-ups may be needed to unravel temporal associations between poor sleep and cognitive impairment, Pase noted.

"Having established the Sleep and Dementia Consortium, we now have a resource to examine other important questions, including which aspects of sleep are most strongly related to the risk of dementia up to 20 years in the future," he said.

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