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Fascinating research on how breathwork can clean your brain: Wisdom Wednesdays · Hardiness with Dr Paul Taylor

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  Speaker 1: Hey everybody, welcome to another edition of Wisdom Wednesdays. Now
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  Speaker 1: I came across a series of research papers recently that
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  Speaker 1: I think are absolutely fascinating and they connect three things
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  Speaker 1: that on the surface don't seem like they should have
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  Speaker 1: much to do with each other and it's breathing, carbon
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  Speaker 1: dioxide and the brain's waste clearance system called the glymphatic system.
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  Speaker 1: And the researchers may have come across a mechanism to
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  Speaker 1: improve brain health and and even reduce your risk of
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  Speaker 1: developing Alzheimer's disease. Now, it's early research, but the mechanism
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  Speaker 1: is pretty fascinating, and it may give us another reason
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  Speaker 1: to pay attention to something I've spoken about for years,
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  Speaker 1: which is the power of breath work. So let's dive
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  Speaker 1: into it. Now, you may have heard me talk before
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  Speaker 1: about the glymphatic system. Think of it as part of
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  Speaker 1: the brain's housekeeping system and the brain's equivalent to the
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  Speaker 1: body's lymphatic system. So in the brain's glymphatic system, so
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  Speaker 1: it's lymphatic with a G, cerebral spinal fluid, that fluid
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  Speaker 1: around your brain and spinal cord, it moves through and
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  Speaker 1: around your brain tissue. And what it does, part of
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  Speaker 1: its job is to help transport metabolic waste products away
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  Speaker 1: from the neurons when they dump them into the cerebral
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  Speaker 1: spinal fluid. And some of those waste products are proteins
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  Speaker 1: that we really do not want accumulating in excessive amounts.
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  Speaker 1: Things like amyloid beta, tau and alpha-synuclein, which are all
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  Speaker 1: associated with Alzheimer's disease, Parkinson's disease and some other forms
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  Speaker 1: of neurodegeneration. You may have heard of them before. Now,
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  Speaker 1: for years, one of the big things we've known about
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  Speaker 1: the glymphatic system is that it becomes particularly active during sleep.
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  Speaker 1: But researchers at the University of New Mexico and the
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  Speaker 1: MIND Research Network, including Dr. Sophia Ryman, have been asking
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  Speaker 1: a really interesting question. What actually drives that flow of
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  Speaker 1: the cerebral spinal fluid? And could we deliberately stimulate it
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  Speaker 1: while we're awake? And one of the answers may be
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  Speaker 1: something called vasomotion. Now, your cerebral blood vessels, they don't
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  Speaker 1: just sit there at a fixed diameter. They actually expand
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  Speaker 1: and contract. And when the volume of blood inside the
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  Speaker 1: skull changes, cerebral spinal fluid has to move as well.
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  Speaker 1: And because the skull, after all, is a pretty fixed box.
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  Speaker 1: So imagine those blood vessels rhythmically expanding and contracting, almost
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  Speaker 1: like a very slow pump. And recent research has shown
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  Speaker 1: that during non-REM sleep, levels of norepinephrine in the brain,
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  Speaker 1: which the Yanks call it norepinephrine, we call it noradrenaline,
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  Speaker 1: Levels of that in the brain oscillate at a remarkably
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  Speaker 1: slow rhythm, roughly once every 50 seconds. Now, that's important.
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  Speaker 1: Hold on to that once every 50 seconds. Those oscillations
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  Speaker 1: cause the arteries to constrict and dilate, producing corresponding waves
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  Speaker 1: in the cerebral spinal fluid, which is one of the
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  Speaker 1: mechanisms by which that movement of the cerebral spinal fluid
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  Speaker 1: appears to act like a pumping mechanism for the glymphatic system,
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  Speaker 1: helping move fluid through the spaces around blood vessels and
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  Speaker 1: through brain tissue, carrying metabolic waste products away from the brain.
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  Speaker 1: But there's another powerful way to make cerebral blood vessels expand.
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  Speaker 1: And it's something that most of us think of as
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  Speaker 1: a waste gas and it's carbon dioxide or CO2. Now,
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  Speaker 1: this is where the first experiment gets really interesting. So
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  Speaker 1: in a 2025 study, Ryman and colleagues studied healthier, older
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  Speaker 1: adults and people with Parkinson's disease. In these patients, they
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  Speaker 1: experimentally manipulated their carbon dioxide levels. So participants alternated between
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  Speaker 1: breathing normal air and breathing air containing increased amounts of CO2.
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  Speaker 1: So essentially, it was a kind of a rhythm of
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  Speaker 1: high CO2, normal CO2, high CO2, normal CO2, high CO2.
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  Speaker 1: And they pretty much mimicked the timing of those natural
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  Speaker 1: oscillations I mentioned earlier, the 50 second oscillation that we've
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  Speaker 1: seen that's important in the glymphatic system. And they did
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  Speaker 1: three roughly 10 minute sessions. That was about 30 minutes
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  Speaker 1: in total over the day. And as the carbon dioxide increased,
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  Speaker 1: the cerebral blood vessels dilated significantly. As it decreased, they constricted.
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  Speaker 1: And that rhythmic vasomotion was accompanied by increased movement of
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  Speaker 1: the cerebral spinal fluid. In other words, they appeared to
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  Speaker 1: be creating a pump in the brain by manipulating the
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  Speaker 1: level of carbon dioxide. But then they measured what appeared
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  Speaker 1: in the blood. And after the intermittent CO2 exposure, they
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  Speaker 1: detected increased concentration of a whole collection of brain-derived proteins,
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  Speaker 1: including alpha-synuclein, alpha-loid beta-40 and 42, neurofilament-light GFAP, and phospholated tau-217. Now,
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  Speaker 1: the interpretation is that increasing their appearance in the blood
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  Speaker 1: may indicate that these substances were being moved out of
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  Speaker 1: the brain and because of the increased movement of the
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  Speaker 1: cerebral spinal fluid, that vasomotion. Now, this doesn't prove that
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  Speaker 1: they had suddenly cleaned amyloid plaques and other things out
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  Speaker 1: of somebody's brain, but the evidence is consistent with increased clearance. Then,
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  Speaker 1: in 2026, the same group published an even more interesting experiment.
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  Speaker 1: This time, they studied 44 people, 22 healthy controls, and
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  Speaker 1: 22 people with chronic traumatic brain injury. Again, they created
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  Speaker 1: oscillations in CO2 for about 30 minutes. They measured several
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  Speaker 1: brain derived proteins before the intervention and then repeatedly afterwards.
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  Speaker 1: And here's what happened. At about 45 minutes after the
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  Speaker 1: CO2 intervention and GFAP increased significantly in the blood. Neurofilament
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  Speaker 1: light increased and brain-derived tau increased significantly. And then around
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  Speaker 1: the 90-minute mark, something really interesting happened. The concentrations fell
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  Speaker 1: below their starting levels. And by about two and a
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  Speaker 1: half hours, they had largely returned towards baseline. So they,
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  Speaker 1: the authors, they described this as initial protein efflux followed
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  Speaker 1: by potential depletion. right? Now that is pretty bloody interesting,
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  Speaker 1: but blood biomarkers are not the same thing of taking
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  Speaker 1: a biopsy of someone's brain and proving that you've removed
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  Speaker 1: the tau and the other nasty proteins from the brain tissue.
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  Speaker 1: And the authors did acknowledge that limitation, but the pattern
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  Speaker 1: is exactly what you'd expect to see if you temporarily
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  Speaker 1: increase movement of these proteins out of the brain and
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  Speaker 1: and into the circulation. And that is a really interesting finding.
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  Speaker 1: And now we get to the part that really caught
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  Speaker 1: my attention, because you might quite reasonably be saying, hey,
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  Speaker 1: that's great, but I'm not going to sit in an
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  Speaker 1: MRI scanner breathing 5% carbon dioxide. Fair point. But what
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  Speaker 1: else increases CO2? And that is where the third paper
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  Speaker 1: comes in. Ryman and colleagues published a paper called Harnessing
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  Speaker 1: Brain Rhythms to Activate the Glymphatic Pathway via Controlled Breathing
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  Speaker 1: and Intermittent CO2. And they put forward what I think
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  Speaker 1: is a pretty fascinating hypothesis and a pretty solid one
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  Speaker 1: to boot. Now, as I mentioned earlier, during non-REM sleep,
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  Speaker 1: some of the vascular oscillations associated with cerebrospinal fluid movement
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  Speaker 1: occur at around 0.02 hertz. And that means roughly one
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  Speaker 1: cycle every 50 seconds. That's what I talked about right
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  Speaker 1: at the start. And the researchers point out that you
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  Speaker 1: could theoretically produce a similar rhythm while awake using repeated
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  Speaker 1: breath holds. So when you hold your breath, your CO2
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  Speaker 1: starts to rise and then that increased CO2 dilates your
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  Speaker 1: cerebral blood vessels. And then when you resume breathing, normally
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  Speaker 1: the CO2 falls again and the blood vessels or the
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  Speaker 1: vessels begin to constrict. then you repeat it in a
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  Speaker 1: 50-second breath cycle. And I'll get more to that later on.
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  Speaker 1: So rather than CO2 on, CO2 off using a gas cylinder,
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  Speaker 1: you're mimicking it through cycles of breath, hold, breathe, breath, hold, breathe.
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  Speaker 1: And by doing this, you're generating repeated oscillations in the
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  Speaker 1: diameter of your cerebral blood vessels and therefore creating that movement. Now,
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  Speaker 1: the researchers specifically hypothesize that breath hold cycles occurring roughly
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  Speaker 1: every 50 seconds could potentially stimulate the sort of very
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  Speaker 1: slow vasomotion that appears important for glymphatic flow during sleep.
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  Speaker 1: And that's not me extrapolating widely. That's the hypothesis they
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  Speaker 1: actually put forward in the paper. And breathing may potentially
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  Speaker 1: influence your cerebral spinal fluid in another way as well.
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  Speaker 1: Every time your diaphragm moves, you're changing pressure inside your chest,
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  Speaker 1: And those pressure changes affect what's called venous return from
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  Speaker 1: the brain and produce movement of cerebrospinal fluid. breathing may
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  Speaker 1: give you two different mechanisms. Firstly, you've got a mechanical
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  Speaker 1: pump from the pressure changes created by the expansion and
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  Speaker 1: contraction of the diaphragm. And then secondly, you've potentially got
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  Speaker 1: a vascular pump in the brain produced by the oscillations
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  Speaker 1: in carbon dioxide. Now, If you're familiar with pranayama, none
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  Speaker 1: of this sounds particularly exotic. So yogic traditions have been
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  Speaker 1: deliberately manipulating breathing for centuries. And one technique is called kumbhaka,
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  Speaker 1: which essentially involves breath retention. And from a physiological perspective,
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  Speaker 1: that's important because when you stop breathing, your cells don't
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  Speaker 1: stop producing carbon dioxide. So your carbon dioxide goes up.
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  Speaker 1: And this is also the basis of what we call
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  Speaker 1: CO2 tolerance trainings. And I've got a CO2 tolerance protocol
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  Speaker 1: in my app, which we've been using on military guys,
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  Speaker 1: and that uses controlled breath holds. Increasing by about two
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  Speaker 1: seconds every week to help people improve their CO2 tolerance.
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  Speaker 1: But with a slight tweak to that protocol, it might
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  Speaker 1: also help clean the brain of waste products. So as
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  Speaker 1: I said earlier, these researchers suggest breathing cycles of around
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  Speaker 1: 50 seconds. Now that doesn't mean you do a five
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  Speaker 1: second inhale and a 45 second breath hold. it means
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  Speaker 1: that your CO2 should rise and fall about every 50 seconds. Now,
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  Speaker 1: that could be a five-second inhale followed by a 20-second
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  Speaker 1: hold and then 25 seconds of normal breathing. Or it
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  Speaker 1: could be a five-second inhale and a very slow 25-second
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  Speaker 1: exhale and then the rest at normal breathing. But the
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  Speaker 1: key here is a significant rise and fall in CO2
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  Speaker 1: every 50 seconds. Practice for as many cycles as you
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  Speaker 1: have the time or inclination for. And they did three
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  Speaker 1: 10-minute cycles throughout the day. And I want to actually
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  Speaker 1: just cap off this podcast by making a really important
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  Speaker 1: distinction in breathwork modalities. So if your aim is to
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  Speaker 1: create these temporary rises and falls in CO2, you don't
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  Speaker 1: want to do any controlled hyperventilation, which brings me to
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  Speaker 1: the Wim Hof method. Now, I like Wim and I
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  Speaker 1: like the breathing technique he teaches. I've used it myself.
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  Speaker 1: And there's some really interesting physiological effects associated with the
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  Speaker 1: Wim Hof method, such as increases in adrenaline and dopamine
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  Speaker 1: and the priming of the immune system. But from a
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  Speaker 1: CO2 perspective, it is doing almost the exact opposite of
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  Speaker 1: what we're talking about here. The big repeated breaths at
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  Speaker 1: the beginning of the Wim Hof method are essentially a
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  Speaker 1: controlled hyperventilation. and hyperventilation blows off carbon dioxide. So in
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  Speaker 1: the famous 2014 study of Wim Hof from Radboud University,
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  Speaker 1: the trained participants produced what the researchers called an immediate
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  Speaker 1: and profound fall in arterial CO2. The blood then became
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  Speaker 1: markedly alkaline, with the pH reaching as high as 7.75
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  Speaker 1: in some subjects, and then they held their breath. So
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  Speaker 1: during that breath hold, That's when the CO2 begins to climb,
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  Speaker 1: but it's climbing from an artificially low starting point. And
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  Speaker 1: another study gives a really good illustration of this. Researchers
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  Speaker 1: looked at competitive breath-hold divers who hyperventilated before a maximum breath-hold.
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  Speaker 1: And their end tidal CO2 immediately before the breath-hold, after
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  Speaker 1: they'd done the hyperventilation, it averaged only 18.9 millimetres of mercury.
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  Speaker 1: Normal CO2 is roughly 30 to 45. Then these guys
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  Speaker 1: held their breath for an average of 284 seconds. That's
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  Speaker 1: getting close to five minutes. And even after almost five
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  Speaker 1: minutes without breathing, their end tidal CO2 had only climbed
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  Speaker 1: to 38.3 millimetres of mercury. In other words, it had
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  Speaker 1: basically just returned to the normal range. Meanwhile, oxygen had
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  Speaker 1: fallen dramatically. And that's why the controlled hyperventilation allows such
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  Speaker 1: long breath holds. You've removed much of the CO2 signal
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  Speaker 1: that creates the urge for us to breathe. It's not
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  Speaker 1: low oxygen, it's high CO2 that makes you want to breathe.
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  Speaker 1: But it's also why I would not choose the Wim
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  Speaker 1: Hof method if my specific goal was to produce these
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  Speaker 1: controlled hypercapnic oscillations to activate the glymphatic system. Now, Wim
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  Speaker 1: Hof uses largely a hypocapnic hypoxic intervention, which means low CO2,
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  Speaker 1: low oxygen, rather than a straightforward hypoxic hypercapnic, which means
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  Speaker 1: high CO2, which is the one that we're really after,
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  Speaker 1: that oscillating of the CO2. So if you're trying to
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  Speaker 1: replicate what we're talking about in this study, the protocol
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  Speaker 1: is much simpler. It's the kumbhaka or short CO2 tolerance
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  Speaker 1: breath holds. A bit of normal breathing, normal exhalation, then
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  Speaker 1: you do a comfortable breath hold, And then you breathe
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  Speaker 1: normally again. No massive preparatory breaths. You're not trying to
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  Speaker 1: break the breath holding record. It's not a macho competition.
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  Speaker 1: It's just enough of a hold for CO2 to rise. Ideally,
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  Speaker 1: where you feel that little bit of discomfort. And then
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  Speaker 1: you follow it by normal breathing so that it falls again.
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  Speaker 1: And then you repeat. So the point isn't to maximize CO2.
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  Speaker 1: The point is the oscillation. the vascular rhythm that helps
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  Speaker 1: to move your cerebrospinal fluid. Now, I do want to
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  Speaker 1: emphasize again, we don't yet have the study that I'd
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  Speaker 1: really like to see. Nobody's demonstrated that doing this protocol
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  Speaker 1: every morning clears tau from your brain and reduces your
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  Speaker 1: risk of Alzheimer's disease. But what we do have is
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  Speaker 1: evidence that experimentally oscillating CO2 increases cerebral spine fluid movement.
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  Speaker 1: And we have evidence that experimentally oscillating CO2 increases the
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  Speaker 1: appearance or the bringing out of several brain derived proteins
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  Speaker 1: into the blood. which is consistent with efflux or movement
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  Speaker 1: out of the brain. And then we have evidence that
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  Speaker 1: brain-derived tau follows that pattern. And now we have a
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  Speaker 1: biologically plausible argument from the researchers themselves that controlled breath
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  Speaker 1: holding may be able to engage some of these same mechanisms.
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  Speaker 1: And for me, it's pretty fascinating and it's good enough
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  Speaker 1: evidence for me to put this into practice. Because once again,
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  Speaker 1: we have an example of an ancient, breathing practice bumping
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  Speaker 1: into modern physiology. People practicing Kumbhaka thousands of years ago
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  Speaker 1: knew nothing about phosphorylated tau and Alzheimer's disease, cerebrospinal fluid
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  Speaker 1: or glymphatic clearance, but they had discovered a very powerful
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  Speaker 1: way of manipulating human physiology and were only just beginning
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  Speaker 1: to understand what some of those physiological changes may actually do.
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  Speaker 1: So if you're ready, practice breathwork. Here's the takeaway. Don't
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  Speaker 1: assume that every form of breath work does the same thing.
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  Speaker 1: Slow controlled breathing helps to switch on your parasympathetic nervous system.
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  Speaker 1: Wim Hof breathing, you're driving down CO2 and you can
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  Speaker 1: increase your breath hold. But if you're doing Kumbhaka or
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  Speaker 1: CO2 tolerance training without the prior hyperventilation, you're allowing that
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  Speaker 1: CO2 to rise and fall. And I do want to
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  Speaker 1: say one just thing about breath hold. It should be
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  Speaker 1: comfortable and controlled. Do not ever practice prolonged breath holds
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  Speaker 1: in water when you're driving, when you're standing somewhere you
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  Speaker 1: could fall over or in any situation where losing consciousness
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  Speaker 1: would put you at risk. We want to be doing
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  Speaker 1: controlled breath work practices that manipulate our physiology in very
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  Speaker 1: specific ways. So that's it for this week, folks. Catch
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  Speaker 1: you next time.