Research published in Sleep Health reveals that sleep fragmentation significantly impacts mental processing speed in older adults. The study found that the amount of time spent awake in bed after initially falling asleep correlates with slower cognitive performance the following day. This suggests that sleep continuity may be more crucial for cognitive function in later life than total sleep duration.

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Investigating the relationship between sleep and cognitive maintenance in older age, the study sought to track day-to-day variations in sleep and cognitive performance. Researchers focused on older adults without dementia to determine if sleep disturbances might indicate future cognitive issues, potentially guiding preventative measures against conditions like Alzheimer’s disease.

Orfeu M. Buxton, a lead author and professor at Pennsylvania State University, emphasized the need for understanding sleep's role in cognitive decline, particularly in light of a 2024 Lancet Commission report that noted a lack of clarity on whether sleep problems precede or follow cognitive impairment.

The team analyzed data from the Einstein Aging Study, including 261 diverse participants aged 70 and older, who were free of dementia. Over 16 days, participants wore Actiwatch devices to objectively measure their sleep patterns and completed cognitive tests using smartphones at six intervals throughout the day.

The cognitive assessments focused on tasks affected by aging, including visuospatial working memory and processing speed. Researchers specifically analyzed sleep characteristics, paying close attention to Wake After Sleep Onset (WASO), which indicates fragmented sleep.

Statistical analysis revealed that greater sleep fragmentation was associated with poorer cognitive performance across various measures, particularly in processing speed. Adjustments for potential confounding factors, including age, race, education, and health conditions, confirmed these findings.

The study examined both between-person and within-person effects, showing that individuals with higher sleep fragmentation generally performed worse on cognitive tasks. Importantly, even slight increases in wakefulness during the night correlated with slower processing speeds the next day.

The results indicated that overall sleep duration did not significantly predict cognitive performance, aligning with previous research suggesting that sleep quality may be more important than quantity for older adults. Buxton noted that a better night’s sleep with fewer disruptions was related to improved cognitive function the following day.

The authors proposed potential biological mechanisms explaining the impact of disrupted sleep on cognitive speed, such as interference with the brain's glymphatic system, which is active during deep sleep and responsible for clearing waste.

While this study provides insights into the day-to-day dynamics of sleep and cognition, its 16-day assessment period may not capture longer-term patterns. Further research is needed to explore the long-term impacts of sleep quality on cognitive decline.

The study was conducted by a team that includes Buxton, Qi Gao, Jonathan G. Hakun, Linying Ji, Alyssa A. Gamaldo, Suzanne M. Bertisch, Martin J. Sliwinski, Cuiling Wang, and Carol A. Derby.