Across the body

Brain, Spine, Muscle and Nerve Conditions and Surgery

Across the body

Brain, Spine, Muscle and Nerve Conditions and Surgery

Neurology, developmental medicine, and neurosurgery are medical specialties that focus on the form, function, and health of the nervous system, which includes the central (CNS) and peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, whereas the PNS includes everything from the nerves that leave our brain and spinal cord to the interaction of those nerves with other nerves or muscles and the muscles themselves. Because sleep and circadian health are primarily neurologic processes, there is a whole lot for us to unpack on the relationship with neurology-based disorders.

The nervous system is quite dynamic, and from the time a developing fetus is in utero, the nervous system is already developing and maturing, and this continues until we are in our 30s. Across our lives, there are many factors that contribute to the overall health of our nervous system, and, of course, sleep and circadian factors are critically relevant. 

Neurodegenerative Diseases and Sleep

Neurodegenerative diseases are conditions that cause progressive changes to the brain and nervous system, resulting in symptoms and function that worsen over time. Understanding how sleep and circadian rhythms interconnect with these brain diseases is vitally important. 

We continue to see that the story about sleep and circadian health and its relationship with overall brain health continues to develop, with more details emerging. However, an ongoing theme consistently demonstrates that poor-quality sleep and disturbed circadian rhythms can both signal, or be a sign of, as well as be a cause or exacerbating factor for neurodegenerative diseases, like Alzheimer’s disease (AD) and Parkinson’s disease (PD). What do we mean? 

Brain disorders can result in the development or worsening of sleep and circadian problems.1,2 Alternatively, having a chronic sleep or circadian disorder creates a less healthy brain environment, which can result in a higher likelihood of developing neurodegenerative conditions. The result? An ugly cycle that has the potential to speed up disease progression. Of course, other individual factors also play a role, like our genetics, environment, and other health considerations. However, if we can use this understanding of the full 24 hours to optimize our brain performance and overall health while also helping us sleep better, then sign us up.

In general, over the course of 24 hours, expected biological processes occur when we are both asleep and awake. Some of these processes are critically aligned with having an expected timing, regularity, and duration of our sleep. For instance, during wakefulness, our brain is very active, producing remnants from this activity that circulate in the cerebrospinal fluid (CSF) and only increase with wakefulness and, if not cleared, can be damaging to the brain. During sleep, especially deep or slow-wave sleep, there is a marked increase in the brain’s ability to clear these waste products, including toxins such as beta-amyloid (A𝛽), one of the culprits for AD, through the glymphatic system.3 Think of it kind of like the CNS equivalent of our lymphatic system, or the system that helps our body get rid of waste and protects us from illness and infection.

Our brain environment is highly regulated by specialized cells and structures, such as the covering of the brain or meninges, specialized blood vessels, and specific nerve cells called glial cells. The combination of some of these creates the blood-brain barrier, essentially a filter that selects what gets in. On the other hand, the glymphatic (think combo of glial and lymphatic) system is a system of vessels that is highly responsible for getting things out of the CNS and is highly active at night while we sleep, especially during deep or slow-wave sleep. Clearly, a well-matched duo, at least when they are on the same rhythm. 

What happens when we fall out of sync? Let’s take a look at two neurodegenerative diseases—PD and AD—and see. 

PD and Sleep 

Did you know that sleep symptoms, especially excessive daytime sleepiness, are one of the most commonly encountered nonmotor symptoms of PD? In fact, most people with PD have at least one sleep problem, and sometimes these can be present as a clue that a person is at risk for PD. REM sleep behavior disorder (RBD) has long been associated with PD and is a condition that raises concern for the future development of PD. RBD more commonly develops in people between the ages of 50 and 60 and may be present before any other symptoms of PD occur.  It is important to distinguish that RBD is not exclusive to PD and can be seen in conditions like narcolepsy or withdrawal from certain psychiatric medications and may not be related to PD at all. 

Scientific evidence4 shows that when people with RBD are studied for more than 10 years, between 80% and 90% of them will develop PD or a Parkinson-like disorder. Those people with RBD who eventually develop PD are more likely to have rapidly worsening symptoms. Having a sleep disorder, not including obstructive sleep apnea (OSA) but particularly insomnia, is associated with an increased risk of developing PD. Whether (1) the early changes in the brains of people with PD affect their circadian rhythm or sleep-wake circuits or (2) the sleep disturbances hasten the progression of PD is both likely and not mutually exclusive.

Sleep and AD

As in PD, people who have a sleep or circadian disorder, such as disrupted circadian rhythm, insomnia, or OSA, are more likely to develop AD. In fact, longitudinal studies5,6 (meaning research studies that follow people over an extended period of time to assess a specific question or series of questions) demonstrate that more suppressed, unstable, and fragmented daily activity rhythms are associated with a higher risk of developing AD dementia in older people with normal to mildly impaired cognition, but also increase the risk for those with mild cognitive impairment to convert to AD.  

People living with AD have a progressive circadian dysregulation and cognitive impairment that far exceeds age-expected changes over time. Between 25% and 60% of people with AD have a sleep disorder; more than half have insomnia.7 People with AD often have fragmented sleep (they sleep for a brief period, wake up, return to sleep, wake up again, over and over throughout the night), are more easily awakened at night, and are less active during the day, as compared with people without AD. As you can imagine, this fragmented sleep is disruptive not only for the person with AD but also for their family and caregivers. 

Researchers have shown that restricting sleep for even a single night can lead to a buildup of amyloid-β protein in the brain. If those nights of sleep deprivation pile up, the buildup of amyloid-β may pave the road toward Alzheimer’s disease.

Is it Possible to Boost my Glymphatic System? 

The best way to help your brain remove the toxins that accumulate throughout the day starts at night. First and foremost among the recommendations is to get a good night’s sleep—making sure that you get plenty of slow-wave or deep sleep. This means good sleep hygiene and habits that ensure enough time for sleep at the right time of the light-dark or circadian cycle. In addition, exercise, no or low amounts of alcohol, blood pressure control, and a healthy diet (one that is high in omega-3 fatty acids). Foods that are high in omega-3 fatty acids are fatty fish, walnuts, flaxseeds, soy beans, and chia seeds. 

HOT OFF THE PRESS!

A new study9 examining sleep among 733 women in their 80s who live in their homes found that increasing sleepiness increased the risk for developing dementia. At baseline and 5 years later, the women wore actigraphs (see the diagnosing sleep disorders section of the website) that measured the length of daytime naps and nighttime sleep. During the 5-year study period, 164 women developed mild cognitive impairment, a change in thinking and memory, and another 93 were diagnosed with dementia. After accounting for other health conditions, researchers found that increased sleepiness (that is, longer total sleep duration) doubled the participants’ risk of developing dementia, as compared to those participants who had no change in their sleep.

Back to the chicken and egg phenomenon, was the sleepiness a risk factor for or a sign of the dementia? We are back to thinking about that bidirectional relationship in which brain disease increases the risk of having disturbed sleep, and disturbed sleep increases the risk of developing brain disease. As the authors of this study said, “concurrent declines in sleep health and cognition may exacerbate one another, creating a vicious cycle and accelerating deterioration in both.”9

References

  1. Khandayataray P, Murthy MK. Exploring the nexus: sleep disorders, circadian dysregulation, and Alzheimer’s disease. Neuroscience. 2025;574:21-41.
  2. Nassan M, Videnovic A. Circadian rhythms in neurodegenerative disorders. Nat Rev Neurol. 2022;18(1):7-24.
  3. Kylkilahti TM, Berends E, Ramos M, et al. Achieving brain clearance and preventing neurodegenerative diseases–a glymphatic perspective. J Cereb Blood Flow Metab. 2021;41(9):2137-2149.
  4. Antelmi E, Lanza G, Mogavero MP, et al. Intersection of sleep disorders and Parkinson disease: unveiling the bidirectional relationship. Mov Disord Clin Pract. 2025;12(1):11-20.
  5. Duncan MJ, Guerriero LE, Kohler K, et al. Chronic fragmentation of the daily sleep-wake rhythm increases amyloid-beta levels and neuroinflammation in the 3xTg-AD mouse model of Alzheimer’s disease. Neuroscience. 2022;481:111-122.
  6. Van Egroo M, van Someren EJW, Grinberg LT, Bennett DA, Jacobs HIL. Associations of 24-hour rest-activity rhythm fragmentation, cognitive decline, and postmortem locus coeruleus hypopigmentation in Alzheimer’s disease. Ann Neurol. 2024;95(4):653-664.
  7. Benca R, Herring WJ, Khandker R, Qureshi ZP. Burden of Insomnia and sleep disturbances and the impact of sleep treatments in patients with probable or possible alzheimer’s disease: a structured literature review. J Alzheimers Dis. 2022;86(1):83-109.
  8. Morse A, Kothare S. Cross linkage between quality of sleep and neurologic conditions in age-diverse populations. Astrocyte. 2018;5(1):63.
  9. Milton S, Cavailles C, Ancoli-Israel S, Stone KL, Yaffe K, Leng Y. Five-year changes in 24-hour sleep-wake activity and dementia risk in oldest old women. Neurology. 2025;104(8):e213403.