What is the glymphatic system?
Your brain has its own built-in waste-removal network, called the glymphatic system. Researchers first described it in 2012 (Iliff et al., 2012). It works like a network of tiny drainage channels that wash away proteins and other waste that build up during the day.
Think of it as the overnight cleaning crew for your brain. It does its best work when the lights go out.
How it works
Cerebrospinal fluid (CSF) is the clear fluid that surrounds your brain and spinal cord. It flows along the spaces around your brain’s arteries, picks up waste from brain tissue, and carries it out along veins and lymphatic vessels in the lining of your skull (Louveau et al., 2015).
Special water channels called aquaporin-4 (AQP4) sit on star-shaped brain cells called astrocytes. They help fluid move in and out of brain tissue.
Two natural pumps help push the fluid along:
- Your heartbeat. Each pulse makes the brain’s arteries widen slightly.
- Your breathing. Each breath changes the pressure in your chest, which moves CSF up and down (Dreha-Kulaczewski et al., 2015).
Scientists still debate how much fluid moves and what drives it, so this picture is still being refined (Hladky & Barrand, 2022).
Why sleep is essential
The cleaning crew is far more active during deep (NREM) sleep than when you are awake. In mice, the spaces between brain cells expand by about 60% during sleep, so fluid flows through more easily (Xie et al., 2013). In people, deep sleep brings slow, rhythmic waves of CSF flow (Fultz et al., 2019).
Human evidence is growing:
- In a tracer study, a night without sleep slowed the clearance of a tracer from the brain (Eide et al., 2021).
- In a 2026 randomized crossover study of 39 people, blood levels of amyloid-beta and tau were higher after normal sleep than after sleep deprivation. This fits with the brain moving these proteins out into the blood (Dagum et al., 2026).
What happens when it slows down?
When glymphatic function declines, waste can build up in the brain. Ageing, poor sleep, chronic stress, certain health conditions and head injuries can all slow it down. Reduced clearance is increasingly linked to:
- Alzheimer’s disease and cognitive decline
- Parkinson’s disease and related conditions
- Traumatic brain injury and post-concussion problems
- Stroke recovery
- Poor sleep and chronic stress
These are links, not proven causes. Researchers are still working out which comes first.
What can support it?
Sleep has the strongest human evidence. Most other supports are early, or come from animal studies.
| Practice | What the research shows | Evidence in humans |
|---|---|---|
| Quality sleep, especially deep sleep | Boosts clearance of waste proteins | Strongest |
| Side (lateral) sleeping | Better drainage than stomach sleeping in animal studies (Lee et al., 2015) | Not yet tested |
| Regular exercise | A 12-week cycling programme increased measures of brain fluid exchange in a small study (reviewed in Wrzesień et al., 2026) | Early |
| Omega-3 fats (fish, flaxseed, walnuts) | May help AQP4 water channels work better in animal studies | Animal studies only |
| Stress reduction | Chronic stress hormones affecting astrocytes may impair the system | Mechanistic |
| Slow deep breathing | Increases CSF movement in awake adults | Fluid movement shown, clearance not measured |
| Mind-body practices (yoga, meditation, tai chi) | Yoga improves sleep quality; direct glymphatic research is just beginning | Preliminary |
Where yoga fits in
Direct research on yoga and the glymphatic system is still emerging. Yet yoga works on several things that do matter:
- Better sleep. Yoga consistently improves sleep quality.
- Less stress. Lower stress hormones may protect the AQP4 water channels.
- Breathing and posture. Breath is one of the two natural pumps that move CSF.
- Movement and circulation. Exercise-type benefits for the lymphatic vessels.
Breath is the best-studied link so far. In 2025, MRI scans of 45 adults (20 trained in slow lower-abdominal breathing, 25 untrained) showed that slow deep breathing increased CSF movement and net flow, especially at the base of the skull (Lim et al., 2025). In an earlier study of 18 healthy adults, funded by the U.S. National Center for Complementary and Integrative Health (NCCIH), four yogic breathing patterns increased the upward flow of CSF compared with normal breathing. Deep belly breathing had the biggest effect and more than doubled the part of CSF movement driven by breathing (Yildiz et al., 2022).
These studies measured how fluid moves. They did not measure how much waste was cleared (Wrzesień et al., 2026).
Skull Shining Breath (Kapalabhati) and CO₂ tolerance: what the research says
No study has yet tested Kapalabhati or CO₂ tolerance training on glymphatic function. What exists are pieces of the puzzle, and they do not all point the same way.
| Question | What the research shows | Evidence |
|---|---|---|
| Does slow deep breathing move CSF? | Yes. In awake adults it increased CSF displacement and net flow (Lim et al., 2025) | Human MRI |
| Do brief swings in CO₂ drive CSF inflow? | Yes, in a lab study with controlled gas. Blood levels of brain proteins also rose, but better clearance is unconfirmed (Erhardt et al., 2025) | Small human study |
| What does Kapalabhati do to brain blood flow? | In 18 healthy young adults, one minute lowered blood-flow speed in a main brain artery and raised vessel resistance (Nivethitha et al., 2017) | Small human study |
Why CO₂ matters to the brain
CO₂ is the main chemical signal that sets how wide your brain’s blood vessels are. More CO₂ widens them. Less CO₂, as happens with over-breathing, narrows them (PET study of nine healthy adults). Glymphatic flow is helped by pulsing and by slow, rhythmic widening and narrowing of brain vessels. In mice, these slow vessel rhythms, driven by norepinephrine, help power clearance during sleep (Hauglund et al., 2025). So CO₂ is a plausible lever.
What is CO₂ tolerance?
CO₂ tolerance describes how comfortably you handle rising CO₂ before you feel a strong urge to breathe. Many breathwork teachers check it with a breath-hold test such as the BOLT score (McKeown, 2015). It is an informal screening tool, not a medical test. The link between CO₂ tolerance and glymphatic health is a hypothesis built from the physiology above, not a research finding.
The closest evidence: brief CO₂ swings
In a 2025 study, older adults, some with Parkinson’s disease, breathed short doses of CO₂ from a monitored gas system, alternating with normal air. The brain’s blood vessels widened and narrowed in a rhythm, and more CSF flowed into the brain. After three 10-minute sessions, blood levels of several brain proteins rose, including amyloid-beta and tau. The response was weaker in Parkinson’s disease (Erhardt et al., 2025). A 2026 review calls this promising but unreplicated, and notes that higher blood levels do not prove better clearance (Wrzesień et al., 2026). The study used lab-controlled gas. A breathing practice cannot copy it.
Skull Shining Breath (Kapalabhati)
Kapalabhati means “skull shining.” The Hatha Yoga Pradipika lists it among the cleansing practices, describing quick, bellows-like breathing (Muktibodhananda, 1985). In practice it uses quick, forceful exhales driven by the belly, with passive inhales, often at about two breaths per second (Kapalabhati fNIRS study).
In the 2017 transcranial Doppler study, one minute of Kapalabhati lowered blood-flow speed in the middle cerebral artery and raised vessel resistance. Holding the breath after a full exhale did the opposite: more flow and less resistance (Nivethitha et al., 2017). This fits the physiology. Fast breathing blows off CO₂, which narrows brain vessels. A breath hold lets CO₂ build up, which widens them.
So Kapalabhati is a short, energising, CO₂-lowering practice. That is different from the slow deep breathing that moved CSF in the MRI studies. Whether the swing in CO₂ across rounds, followed by the quiet pause afterwards, could create helpful vessel rhythms is an interesting question. Worth further research!
Key takeaways
- Your brain clears waste more actively while you sleep, especially in deep sleep.
- Sleep has the strongest human evidence. Slow deep breathing moves CSF in awake adults. Exercise looks promising.
- Kapalabhati and CO₂ tolerance have not been tested for glymphatic effects. They are ideas worth studying, not proven benefits.
Important notes
- Research on mind-body practice and glymphatic function is preliminary and mechanistic. Yoga and breathing are supportive, not a treatment for neurological disease.
- If you have concerns about memory, sleep or neurological symptoms, please talk with your healthcare provider.
- This post is educational. It describes research and general practices. It does not diagnose or treat any condition.
References
Research
- Dagum P, Elbert DL, Giovangrandi L, et al. (2026). The glymphatic system clears amyloid beta and tau from brain to plasma in humans. Nature Communications 17:715. doi:10.1038/s41467-026-68374-8
- Dreha-Kulaczewski S, Joseph AA, Merboldt KD, et al. (2015). Inspiration is the major regulator of human CSF flow. Journal of Neuroscience 35:2485-2491. doi:10.1523/JNEUROSCI.3246-14.2015
- Eide PK, Vinje V, Pripp AH, Mardal KA, Ringstad G (2021). Sleep deprivation impairs molecular clearance from the human brain. Brain 144:863-874. doi:10.1093/brain/awaa443
- Erhardt EB, Mayer AR, Lin HC, et al. (2025). The influence of intermittent hypercapnia on cerebrospinal fluid flow and clearance in Parkinson’s disease and healthy older adults. npj Parkinson’s Disease 11:334. doi:10.1038/s41531-025-01179-6
- Fultz NE, Bonmassar G, Setsompop K, et al. (2019). Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science 366:628-631. doi:10.1126/science.aax5440
- Hauglund NL, Andersen M, Tokarska K, et al. (2025). Norepinephrine-mediated slow vasomotion drives glymphatic clearance during sleep. Cell 188:606-622. doi:10.1016/j.cell.2024.11.027
- Hladky SB, Barrand MA (2022). The glymphatic hypothesis: the theory and the evidence. Fluids and Barriers of the CNS 19:9. doi:10.1186/s12987-021-00282-z
- Iliff JJ, Wang M, Liao Y, et al. (2012). A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid beta. Science Translational Medicine 4:147ra111. doi:10.1126/scitranslmed.3003748
- Lee H, Xie L, Yu M, et al. (2015). The effect of body posture on brain glymphatic transport. Journal of Neuroscience 35:11034-11044. doi:10.1523/JNEUROSCI.1625-15.2015
- Lim S, Cogswell PM, Jacobson DN, et al. (2025). Human cerebrospinal fluid net flow enhanced by respiration during the awake state. Nature Communications 16:11499. doi:10.1038/s41467-025-66548-4
- Louveau A, Smirnov I, Keyes TJ, et al. (2015). Structural and functional features of central nervous system lymphatic vessels. Nature 523:337-341. doi:10.1038/nature14432
- Nivethitha L, Mooventhan A, Manjunath NK, et al. (2017). Cerebrovascular hemodynamics during the practice of Bhramari pranayama, Kapalbhati and Bahir-Kumbhaka: an exploratory study. Applied Psychophysiology and Biofeedback. Springer
- Wrzesień MM, Poboży K, Turek G, Czyzewski W, Zhu B, Ząbek M (2026). Modifiable glymphatic-related brain clearance physiology in humans: a critical narrative review of interventional evidence. Frontiers in Neuroscience20:1984401. doi:10.3389/fnins.2026.1984401
- Xie L, Kang H, Xu Q, et al. (2013). Sleep drives metabolite clearance from the adult brain. Science 342:373-377. doi:10.1126/science.1241224
- Yildiz S, et al. (2022). Immediate impact of yogic breathing on pulsatile cerebrospinal fluid dynamics. NCCIH research summary
- Changes in human cerebral blood flow and cerebral blood volume during hypercapnia and hypocapnia measured by positron emission tomography (2003). PubMed 12796714
- Frontal hemodynamic responses to high frequency yoga breathing in schizophrenia: a functional near-infrared spectroscopy study. PMC3970016
Further reading on Kapalabhati
- Budhi RB, Singh D, Goswami J, Manjunath NK, Vinchurkar S (2024). Influence of high-frequency yoga breathing (Kapalabhati) on states changes in gamma oscillation. International Journal of Yoga 17(2):106-115. doi:10.4103/ijoy.ijoy_5_24
Books
- Brown RP, Gerbarg PL (2012). The Healing Power of the Breath. Shambhala.
- Iyengar BKS (1981). Light on Pranayama. Crossroad.
- McKeown P (2015). The Oxygen Advantage.
- Muktibodhananda S (1985). Hatha Yoga Pradipika. Bihar School of Yoga.
- Nestor J (2020). Breath: The New Science of a Lost Art. Riverhead Books.
- Porges SW (2011). The Polyvagal Theory. W. W. Norton.
