We know that sleep helps us feel rested and energized to go about our day, but what does it do to the brain? Studies have shown that during sleep, our brain clears out proteins and chemicals including amyloid beta, which is one of the proteins involved in Alzheimer’s Disease. In a systematic review by Gonzales et al., the researchers found a connection between disordered sleep and AD, with 45% of those with cognitive impairment having experienced sleep disturbances before the onset of their disease. Further, sleep disorders were prevalent in 55.9% of those with AD but only 15.2% of individuals without AD.
Using advanced imaging technology such as PET scans, researchers have also been able to determine that the number of hours you sleep per night is inversely correlated to the burden of amyloid beta in the brain, with people who sleep more than 7 hours per night having the lowest burden and those who sleep less than 6 hours per night having the highest burden. In other words, the less you sleep, the more amyloid beta you have in your brain and the greater your risk of cognitive decline. Furthermore, those with insomnia have been found to have greater burdens of both amyloid beta and tau due to higher levels of inflammation. Those with obstructive sleep apnea experience periods of decreased brain oxygenation, which leads to greater production of amyloid beta, which adds to the decreased clearance that comes with disturbance of sleep. Disruptions in sleep-wake cycles are again associated with increased amyloid beta burden. Sleeping at night is suggested to be protective against increased levels of amyloid beta, while sleeping during the day contributes to greater burden, specifically in areas of the brain found to be affected first by AD. Moreover, by looking at brain waves measured from an electroencephalogram (EEG) during sleep, researchers have found fewer K-complexes (patterns which are thought to be involved in memory consolidation), in brain areas associated with memory. This increased burden is what links disruptive sleep to nearly twice the risk of cognitive impairment and dementia. Those with fragmented sleep have been found to have a 1.5x increased risk of developing AD. In our own work with WITS, we have shown that hypoxemia caused by obstructive sleep apnea, as well as self-reported poor sleep, may be related to accumulation of tau and contribute to memory loss.
Although the exact mechanism by which sleep increases risk of dementia is unclear, it is clear that good sleep hygiene, including quality and sufficient sleep are important to maximizing health and minimizing risk of cognitive decline. Take this information as permission to wind down early after a long day and prioritize your sleep–it may help your brain stay sharper for longer!
Find WITS research on AD and sleep here:
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Article of Interest:
Gonzales PNG, Villaraza SG, Rosa JCD. The association between sleep and Alzheimer's disease: a systematic review. Dement Neuropsychol. 2024 Aug 26;18:e20230049. doi: 10.1590/1980-5764-DN-2023-0049. PMID: 39193464; PMCID: PMC11348879.
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