Sleep less…remember less: the hidden link between sleep and memory loss

People often don’t get enough sleep for a variety of reasons, ranging from intentional choices like work or study demands (because who needs sleep when you’ve got deadlines, right?), to the growing concern with screen time (a.k.a. the “I’ll just watch one more episode” syndrome), and of course, procrastination (where your brain convinces you that 3 a.m. is a great time to suddenly get productive). But it’s not all fun and games—serious issues like insomnia, sleep apnoea, family responsibilities, or even shift work can also interfere with rest. Sleep disorders are increasingly common, with around one in three people in the UK affected, and they’re particularly prevalent among the elderly. However, not getting enough sleep can increase the risk of developing Alzheimer’s disease (AD).

How do sleep disorders impact Alzheimer’s disease?

Insomnia is characterised by difficulty falling asleep or staying asleep, which can lead to prolonged fatigue and memory issues. As shown in Figure 1, people with insomnia tend to have some similarity in markers as those with Alzheimer’s disease, such as an increased level of Aβ and tau proteins in the brain. This is primarily because a lack of sleep prevents the effective removal of harmful products from the brain – this accumulation increases a person’s risk of AD.

A plethora of experimental studies on humans and animals have shown that lack of sleep can lead to increased circulating levels of TNF-α and the gene resulting in more TNF-α secretion. This pro-inflammatory cytokine exacerbates AD pathology because neuroinflammation can lead to dysfunction and cell death, which are key markers of AD. Other pro-inflammatory cytokines, like IL-1, have been found to be relevant in the link between sleep deprivation and AD. Overexpression of IL-1 in the brain leads to abnormal changes in nerve cell structures especially relating to Aβ plaques. This highlights IL-1’s key role in plaque evolution and the synthesis of Amyloid Precursor Protein, which promotes amyloid production that eventually results in AD pathology. 

What type of sleep can impact one’s risk of Alzheimer’s disease?

Studies using more objective measures, like actigraphy (which tracks sleep-wake activity), found that sleep quality (sleep efficiency) is more important than total sleep time. For example, women with less than 70% sleep efficiency were more likely to experience cognitive impairment. Increased wakefulness during the night also moderated the relationship between amyloid deposition (a hallmark of AD) and memory decline.

Uncertainties…

However, it remains unclear whether poor sleep directly causes AD or if the disease itself leads to sleep disturbances. Some studies suggest a bidirectional relationship. Aging itself leads to poorer sleep quality, including reduced sleep efficiency, less slow-wave sleep (SWS), and more frequent awakenings. Sleep disorders like obstructive sleep apnoea, insomnia, and restless legs syndrome also become more common with age.

What are the next steps?

The good news is that many sleep disorders, including insomnia, are manageable, and improving sleep quality could be a simple yet powerful way to reduce Alzheimer’s risk. Additionally, early diagnosis and treatment of conditions like sleep apnoea and insomnia may help slow or even prevent neurodegenerative changes. s researchers continue to explore the intricate relationship between sleep and Alzheimer’s, one thing is clear: getting a good night’s sleep isn’t just about feeling refreshed. It is a crucial investment in long-term brain health.

Written by Blessing Amo-Konadu

Related articles: Overview of Alzheimer's / Hallmarks of Alzheimer's / CRISPR-Cas9 in AD treatment / Memory erasure

REFERENCES

Lucey, B. (2020). It’s complicated: The relationship between sleep and Alzheimer’s disease in humans. Neurobiology of Disease, [online] 144, p.105031. doi:https://doi.org/10.1016/j.nbd.2020.105031.

NHS (2023). Insomnia. [online] www.nhsinform.scot. Available at: https://www.nhsinform.scot/illnesses-and-conditions/mental-health/insomnia/.

Pelc, C. (2023). Not getting enough deep sleep may increase the risk of developing dementia. [online] Medicalnewstoday.com. Available at: https://www.medicalnewstoday.com/articles/not-getting-enough-deep-sleep-may-increase-dementia-risk#Clarifying-the-link-between-sleep-aging-and-dementia-risk [Accessed 22 Dec. 2024].

Sadeghmousavi, S., Eskian, M., Rahmani, F. and Rezaei, N. (2020). The effect of insomnia on development of Alzheimer’s disease. Journal of Neuroinflammation, 17(1). doi:https://doi.org/10.1186/s12974-020-01960-9.