Sleep and Your Lymphatic System: The Glymphatic Connection
Scientists think your brain may do some of its housekeeping while you sleep. Here’s what the glymphatic system is, what the research does and doesn’t show, and the sleep habits worth keeping either way.
Most of us know the feeling after a short night: a foggy head and a slow start. Brain research over the past decade has offered one possible piece of the explanation, a fluid-clearing system in the brain that seems to work harder during sleep, at least in mice.
That story is often told online with more certainty than the science supports. Here’s what the glymphatic system is, how it connects to the rest of your lymphatic system, what the main studies found and where they disagree. It’s general education, not medical advice.
What is the glymphatic system?
The glymphatic system is a brain-wide pathway in which cerebrospinal fluid, the clear fluid that cushions the brain and spinal cord, flows in along the spaces around arteries, mixes with the fluid between brain cells and drains out along veins, carrying waste with it.
A team led by Maiken Nedergaard at the University of Rochester Medical Center first described the pathway in mice in 2012, in Science Translational Medicine. The name blends “glial,” after the brain’s support cells, with “lymphatic,” because the pathway does a job lymph vessels do elsewhere in the body: collecting fluid from between cells.
Star-shaped glial cells called astrocytes are central to it. They carry water channels called aquaporin-4 where they wrap around blood vessels, and mice bred without aquaporin-4 cleared substances from brain tissue about 70% less effectively. One of those substances was beta-amyloid, a protein that builds up in the brains of people with Alzheimer’s disease. That explains much of the interest in this field, but nothing in this research shows that a sleep habit changes anyone’s risk of disease.
Is the glymphatic system part of the lymphatic system?
Not exactly. The glymphatic system is the brain’s own fluid pathway, but it hands off to the body’s lymphatic system: fluid leaving the brain can drain into lymph vessels in the meninges, the membranes around the brain, and on to lymph nodes in the neck.
Textbooks long said the brain had no lymphatic vessels. Then in 2015, a University of Virginia team reported in Nature that it had found working lymphatic vessels lining large veins in the meninges of mice, connected to the deep cervical lymph nodes in the neck. Elsewhere in the body, lymph travels through vessels with built-in pumps and one-way valves, as our guide to how lymph moves through the body explains.
What happens in your brain while you sleep?
In mice, sleep appears to open up the brain’s fluid channels. In a 2013 study in Science, Nedergaard’s team found that the space between brain cells grew by about 60% during natural sleep or anesthesia, and fluid exchange with the surrounding cerebrospinal fluid rose sharply.
Beta-amyloid also cleared faster during sleep. And when the team blocked norepinephrine, a chemical messenger that helps keep the brain alert, in awake mice, more fluid flowed in, much as it did during sleep. The suggestion: the brain chemistry of wakefulness keeps the channels narrower.
What do human studies show?
Human evidence is thinner, because the mouse methods involve injecting tracers and imaging the brain up close. Two studies are cited most often:
- Waves of fluid during deep sleep. In a 2019 Science study, researchers at Boston University and Massachusetts General Hospital scanned 13 sleeping adults. During non-REM sleep, large waves of cerebrospinal fluid flowed into the brain roughly every 20 seconds, linked to slow brain waves. The study measured fluid movement, not waste clearance.
- Slower clearance after a sleepless night. In a 2021 study in Brain, Oslo researchers injected an MRI tracer into the spinal fluid of 24 adults. The 7 kept awake overnight cleared it more slowly from most brain regions than the 17 who slept, and a recovery night didn’t close the gap. All were patients being assessed for suspected spinal fluid disorders.
How strong is the evidence?
Promising, but far from settled. Most of the research comes from mice and rats, often under anesthesia, the human studies are small, and at least one careful mouse study reached the opposite conclusion.
In 2024, an Imperial College London team reported in Nature Neuroscience that dye clearance from the brains of male mice was markedly reduced, not increased, during sleep and anesthesia. Until labs can explain why their results differ, sleep’s role in brain clearance is an open question.
| Study | Who was studied | What it found | What it can’t tell us |
|---|---|---|---|
| Iliff et al., 2012 | Mice | Described the pathway; clearance fell about 70% without aquaporin-4 | Whether people work the same way |
| Xie et al., 2013 | Mice | Space between brain cells grew about 60% in sleep | Whether human sleep does the same |
| Lee et al., 2015 | Anesthetized rats and mice | Side-lying moved tracer best, belly-down worst | Anything about sleeping people |
| Fultz et al., 2019 | 13 sleeping adults | Large fluid waves during non-REM sleep | Whether the waves remove waste |
| Eide et al., 2021 | 24 adult patients | A sleepless night slowed tracer clearance | How healthy people respond |
| Miao et al., 2024 | Male mice | Clearance fell during sleep and anesthesia | Which methods best reflect natural sleep |
No one has shown that a supplement, massage, gadget or bedtime trick speeds up brain clearance in people. If a product promises that, be skeptical.
Does sleeping position affect glymphatic clearance?
Possibly in rodents, but it’s unproven in people. In a 2015 study in The Journal of Neuroscience, anesthetized rats and mice moved tracer through their brains most efficiently lying on their side, and least efficiently lying on their belly with the head upright.
The researchers, from Stony Brook University and the University of Rochester, speculated that side sleeping, the most popular sleep posture, may have evolved partly to help the brain clear waste, but noted that the finding awaited testing in humans. Lying on the back also did well for clearing beta-amyloid.
So sleep in whatever position helps you sleep soundly. If you sleep on your back with your head slightly raised, as our guide to gentle morning habits for a puffy face suggests, there’s no evidence you’re missing out. Enough unbroken sleep is the part worth focusing on.
Does the rest of your lymphatic system rest at night?
No. Lymph vessels throughout your body keep contracting on their own while you sleep. What drops is the extra help: with your muscles still, there’s less outside squeezing until you get up and move.
That’s one reason a glass of water, a short walk and a few slow belly breaths make a good start to the day. Our 5-minute breathing practice for lymph flow and 10 daily habits for healthy lymph flow show how.
How much sleep do you need?
The CDC recommends at least seven hours a night for adults aged 18 to 60, seven to nine hours for ages 61 to 64, and seven to eight hours for adults 65 and older. Regularity matters too: going to bed and getting up at the same time every day tops the CDC’s list of healthy sleep habits.
What habits help you sleep well?
Most of what helps is simple and free. Based on the CDC’s advice, a workable routine looks like this:
- Fix your wake time. Keep it seven days a week, and count back at least seven hours to set your bedtime.
- Keep caffeine to the morning. The CDC suggests avoiding it in the afternoon and evening.
- Eat and drink early. Avoid large meals and alcohol before bedtime.
- Put screens away. Turn off devices at least 30 minutes before bed, and keep your bedroom quiet, relaxing and cool.
- Wind down your body. Try slow belly breathing or our gentle yoga sequence for lymph flow, which ends with legs up the wall.
- Move during the day. Regular exercise is on the CDC’s list too, and a morning walk puts your leg muscles back to work.
Where does an herbal routine fit?
Alongside good sleep, not instead of it. Cleavera isn’t a sleep aid, and its herbs haven’t been studied for any effect on the glymphatic system.
Our Lymphatic Drainage Drops are an alcohol-free extract of cleavers, red clover, stillingia and prickly ash, herbs traditionally used to support healthy lymphatic flow.* If you like an evening ritual, the second of your two 1 mL servings can go into caffeine-free herbal tea. See how to take lymphatic drainage drops for timing tips, or how it works for the thinking behind the formula.
When to talk to a doctor. This article is general education, not medical advice. See a doctor if you regularly have trouble falling or staying asleep, if you snore loudly or someone notices you stop breathing or gasp in your sleep, or if you feel unusually sleepy during the day. See a doctor promptly about new swelling, especially in one arm or leg, or swelling that comes with pain, redness or warmth.
Cleavera is for adults. Talk to your clinician first if you’re pregnant or nursing, take medication such as blood thinners or hormone therapy, have a hormone-sensitive or bleeding condition, or have surgery scheduled. Our guide to side effects and who should skip lymphatic drops has more.
Frequently asked questions
Does the brain have lymph nodes?
No. The brain itself has no lymph nodes. In mice, fluid leaving the brain drains through lymphatic vessels in the meninges, the membranes around it, to the deep cervical lymph nodes in the neck, according to a 2015 study in Nature. How much this route matters in people is still being studied.
Can you catch up on lost sleep on the weekend?
Not entirely, as far as we know. In the 2021 Oslo study, a night of recovery sleep didn’t make up for slower tracer clearance after a sleepless night, though the study was small and involved patients. The CDC advises going to bed and getting up at the same time every day.
Do naps count toward brain clearance?
Nobody knows. We couldn’t find studies measuring glymphatic activity during daytime naps in people. A short nap can help when you’re tired, but if naps make it harder to fall asleep at night, keep them brief and early, and focus on regular nighttime sleep.
Is it bad to sleep on your stomach?
There’s no human evidence that it harms brain clearance. In the 2015 rodent study, a belly-down position with the head upright moved tracer least efficiently, but those animals were anesthetized and positioned differently from a person asleep in bed. If you sleep well on your stomach, there’s no proven reason to change.
Can lymphatic massage or a supplement help the glymphatic system?
There’s no good evidence that either does. Gentle lymphatic massage works on vessels just under the skin, while the glymphatic pathway sits deep inside the brain. Cleavera’s herbs are traditionally used to support healthy lymphatic flow* in the body, but they haven’t been studied for the glymphatic system.
Sources
- Science Translational Medicine. Iliff JJ, et al. “A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid β.” 2012. pubmed.ncbi.nlm.nih.gov/22896675
- Science. Xie L, et al. “Sleep drives metabolite clearance from the adult brain.” 2013. pubmed.ncbi.nlm.nih.gov/24136970
- The Journal of Neuroscience. Lee H, et al. “The Effect of Body Posture on Brain Glymphatic Transport.” 2015. pubmed.ncbi.nlm.nih.gov/26245965
- Nature. Louveau A, et al. “Structural and functional features of central nervous system lymphatic vessels.” 2015. pubmed.ncbi.nlm.nih.gov/26030524
- Science. Fultz NE, et al. “Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep.” 2019. pubmed.ncbi.nlm.nih.gov/31672896
- Brain. Eide PK, et al. “Sleep deprivation impairs molecular clearance from the human brain.” 2021. pubmed.ncbi.nlm.nih.gov/33829232
- Nature Neuroscience. Miao A, et al. “Brain clearance is reduced during sleep and anesthesia.” 2024. pubmed.ncbi.nlm.nih.gov/38741022
- Centers for Disease Control and Prevention. “About Sleep.” cdc.gov/sleep/about
