Daily rhythm and metabolic syndrome: a study of 272 adults
Study of 272 adults with a wrist device: metabolic syndrome was linked more to heart rate rhythms than to sleep. An association, not a cause.
Blog · Sleep
Sleep and cognitive decline: a review of 17 studies
Review of 17 longitudinal studies: fragmentation, less REM sleep and apnoea are linked to cognitive decline. The evidence is still mixed.
A systematic review published in the Journal of Alzheimer's Disease in 2024 gathered 17 longitudinal studies to find out which objectively measured sleep parameters are associated with cognitive decline.
The authors warn that the findings are promising, but the evidence is still limited: the studies use very different methods. They therefore call for more consistent studies and, in research, for tools that record sleep continuously, such as actigraphy or EEG headbands.
The five sleep biomarkers associated with cognitive decline
The qualitative synthesis of the 17 studies points to five sleep-related predictors of cognitive decline: sleep fragmentation (frequent awakenings, poor continuity), reduced sleep efficiency (the ratio of time asleep to time in bed), reduced REM sleep, increased light sleep (N1/N2 at the expense of deep N3 sleep) and sleep-disordered breathing (apnoea and hypopnoea). Some finer measures of sleep structure were also associated, but results were inconsistent across studies.
The U-shaped relationship with neurodegeneration
Sleep duration shows a U-shaped relationship with later neurodegeneration: both excessive sleep (over 9 hours) and insufficient sleep (under 6 hours) are associated with a higher risk of cognitive decline.
Why REM sleep is studied
REM sleep plays a role in memory processes. Some studies associate its chronic reduction with the build-up of beta-amyloid and tau, the neuropathological markers of Alzheimer's.
The Digital Twin and this research
The Digital Twin lines up the data your devices write to your phone, such as steps, heart rate and sleep, and shows you how they change over time. It does not look for signs of Alzheimer's and it does not diagnose: this research describes groups of people, not you. If you notice changes in your sleep or your memory, talk to your doctor.
The source is at the bottom. Open it.
The source
This summary starts from research by others. It is not medical advice for you: talk it over with your doctor.
- Carpi M. et al., Journal of Alzheimer's Disease (2024), (opens in a new tab)pubmed.ncbi.nlm.nih.gov
Their study. Your data.
Related reading
Early Parkinson’s and REM disorder: a study of 413 people
Study of 413 people with early Parkinson's: probable REM sleep behaviour disorder was linked to faster cognitive decline. An association, not a cause.
Irregular sleep and the heart: a study of 1,992 adults
Study of 1,992 adults: highly variable sleep duration and timing were linked to about double the cardiovascular risk. An association, not a cause.
More studies, same rule: read the source.