#131 - Sleeping with Pets

Hi there, it's Matt here and welcome back to the podcast. Today we are talking about a special topic, pets, in honor of National Pet Day over the weekend. I want you to imagine something. Picture a woman, let's call her Mara. She lived roughly 12,000 years ago somewhere on the edge of what we now call the Near East. The nights where she lives are cold and dark and long. She has fire, she has shelter, she has her small community, and she has something else, something that arrived at the edges of her camp a few generations back drawn by food scraps and proximity. Dogs or nearly dogs, proto-dogs really, the descendants of wolves who at some point made a calculated gamble that the human camp was a better bet than the wilderness. On a cold night, Mara doesn't agonize over whether it's appropriate to let the animals sleep near her. She doesn't wonder if this is good sleep hygiene. She doesn't Google it. She does what the situation calls for. They share warmth. She sleeps. The dog sleeps. One shelter. Now here's what I find remarkable about that image. It is not a metaphor. sentimental reconstruction. It is, as far as we can tell from the genetic, archaeological, and anthropological record, what actually happened. Genetic evidence places the domestication of dogs at least 15,000 years ago, possibly longer. And ethnographic accounts from multiple continents document that humans and their dogs have been sharing sleeping spaces ever since. Indigenous Australians, for instance, were documented sleeping alongside dogs on cold nights specifically for warmth. A practice so embedded in everyday life that it gave rise to an expression we still use today, a three-dog night, uh meaning it's cold enough that you need three dogs pressed against you just to make it to morning. And then something changed. Not the dogs, not the humans, not the biology. What changed was the culture. Somewhere in the centuries of industrialization and urbanization and the rise of what historians call the civilizing process, sleep became private, beds became personal. The idea that an animal sharing your sleeping space was somehow unhygienic, inappropriate, even morally suspect. This idea arrived with the authority of the medical establishment behind it. Many clinicians for decades simply advised patients to get the pet out of the bedroom. No caveats, no nuance, no particular body of evidence to back it up. Here's the thing though, that advice was not ancient wisdom distilled from centuries of careful observation. It was a cultural invention, a relatively recent one, and as we are about to see, the science, when we finally got around to actually doing it, tells a considerably more nuanced and I think considerably more interesting story. Because I want you to hold that context in mind as we go through this episode. We are not asking whether humans should start doing something new and potentially dangerous. We are asking, for the first time with rigorous instruments and proper methodology, what has been happening for 15,000 years. And the scale of the phenomenon we are studying is, when you actually look at it, staggering. Roughly more than half of US households own at least one pet. In Europe, the figures are somewhat similar. And of those pet-owning households, roughly half of dog owners, and even slightly more cat owners, share a bed or bedroom with their animal. Think about that number for a moment. Tens of millions of people every single night curled up with a dog or a cat or both in their sleeping space. This is not the behavior of the unusually eccentric or the sentimentally extreme. This is one of the most common human sleeping arrangements on the planet. And until about a decade ago, almost no one had studied it properly. So, let's fix that. Here is what the science actually says. The good, the complicated, and the genuinely surprising. Let's start with something I find quietly delightful. Dogs, it turns out, may be functioning as living alarm clocks for their owners. Not in the disruptive sense, but in the biological sense. A survey of nearly a thousand adult women across the United States found that dog owners had statistically earlier bedtimes, earlier

wake times, and here's the key part, less variability in their wake times between workdays and weekends compared to women who owned only cats or no pets at all. Now, if you've spent any time on this podcast, you know how much I mention that wake time consistency being one of the fundamental pillars of good sleep. Every time you sleep in on a Saturday to recover from the week, something that, I have to tell you, does not work the way most people imagine, you are shifting your biological clock backward. You are giving yourself a kind of internal jet lag. You are fraying the very circadian rhythm that orchestrates virtually everything your body does well. And here, these dog-owning women were protecting that rhythm, not through discipline or self-deprivation, but through biological demand. The dog needed walking. The dog needed feeding. And so, the owner got up every morning at roughly the same time. Think about what that means. For years, sleep scientists have been urging people to maintain consistent wake times as one of the most important things they can do for sleep health. And this whole time, quietly, reliably, without ever reading a sleep guidebook, the dog was already handling it. There is something almost comedic about this. Something that makes you wonder, not for the first time, who is actually training whom. A partner of today's podcast is Caraway. Now, we are well into the new year, which means that most New Year's resolutions have probably quietly fallen by the wayside, but my promise to cook more at home remains alive, and that is in no small measure due to my Caraway Cookware. Now, I've mentioned it before, I study the neuroscience of sleep, which I think is probably one of the most complex biological systems that we know. Yet, somehow, I cannot cook an egg without creating a carbon-based archaeological artifact. It's terrible. My relationship with cookware previously has been apply heat, forget about it, hear smoke alarm, and then apologize to my wife. But, Caraway ceramic coating is so naturally nonstick that I cannot burn a single thing. It's remarkable. Eggs slide off rather than welding themselves permanently to the pan, and clean up takes just 90 seconds because of that nonstick material. Just add warm water, rinse, and you're done. Also, the non-toxic ceramic coating matters a great deal to me. It is third-party tested, and it has no forever chemicals. That really is essential. I should also note that there are over a hundred thousand people who've given Caraway five-star rating, so I'm not the only one to be raving about them. They've also released a new kitchen timer and an expanded bakeware plus collection. All of that makes me look because I now have it replete in my kitchen as though I've seriously got my kitchen skills together. It's desperately misleading, but it is so appreciated. So, if you buy the cookware set, it will save you up to a hundred and ninety dollars versus buying it all individually. That's what I ended up going for and you can get a discount. So, if you visit carawayhome. com/mattwalker, you will get an additional 10% off. Even an additional 10% off above and beyond the hundred and ninety dollars that you save. So again, that is carawayhome. com/mattwalker or if you're at checkout, just use the code Matt Walker all one word and you will get your discount. So, that's Caraway non-toxic kitchenware made modern. What about the actual quality and architecture of sleep itself? Because that's the harder question. And this is where we need to be precise because the science is more nuanced than either the pet enthusiasts or the sleep purists would have you believe. The best objective study of what a dog actually does to human sleep overnight came from the Mayo Clinic. Researchers recruited 40 healthy adults with no sleep disorders and gave everyone a wrist actigraph, an accelerometer-based device that tracks movement to distinguish sleep from wakefulness. Their dogs were given equivalent monitors. Both wore them for seven consecutive nights in their own homes in their ordinary sleeping arrangements. And then the researchers looked at what sleep scientists call sleep efficiency, the percentage of time spent in bed that you are actually asleep. Think of it like the fuel economy of your night. A

reading of 80% or above is generally considered satisfactory in clinical sleep medicine. The result? When the dog was present somewhere in the bedroom, anywhere in the bedroom, human sleep efficiency averaged 81% above the threshold. Not perfect, but solidly acceptable. The researchers' conclusion was measured and clear. A single dog in the bedroom does not markedly disturb human sleep. But here is where it becomes interesting. The same study found that sleep efficiency dropped significantly when the dog moved from elsewhere in the room onto the bed itself. I have an analogy for this that I think captures it well. Having a dog in your bedroom is like background music playing softly while you try to read. Present, slightly distracting, mostly manageable. Having a dog on your bed is like that music being performed live by a small band who happens to share your mattress, re-positions every 30 minutes, occasionally places a paw directly on your face, and has absolutely no concept of personal space. The difference is not subtle, and the data confirms it. But now, here is the part that truly puzzles me, and I mean genuinely puzzles me, in the best possible way, because the best puzzles in science are the ones that reveal something about how little we actually understand. Multiple independent studies using actigraphy have found the same thing. When dogs move at night, their owners move too. When the dog wakes up, the owner follows, whether they remember it the next morning or not. This is objective. The sensors don't lie. The data shows real measurable disruption at the physiological level. Study after study in different countries with different methodologies finds the same paradox. The accelerometer says disruption. The person says comfort. It's like running every diagnostic on a car and getting multiple warning lights, then having the driver step out and tell you that was the smoothest ride they'd had in years. How do you reconcile that? There are several possible explanations. The first possibility is that the psychological benefit of the animal's presence, the warmth, the sound of breathing, the physical weight of another living creature, the simple fact of not being alone in the dark, genuinely outweighs the physical disruption. Not just masks it, actually outweighs it. The second possibility is that actigraphy, powerful as it is, may be a blunt instrument in this particular context. When two bodies are sharing a surface, the device picks up movement that may not actually represent meaningful disruption to sleep architecture in the way that full gold standard polysomnography would reveal. A third possibility is that we are, at least in part, seeing confirmation bias. People who choose to sleep with their pets are the people who want to sleep with their pets. And that wanting shapes their retrospective experience powerfully. The honest answer is we don't know. And what we don't know matters because the next chapter of the story cuts in a different direction. A partner for today's episode is AG1. I've been using AG1 for quite some time now, and just for the record, I buy it myself to stay away from any of those trappings of free product. AG1 has just released the new formulation, which is AG1 next gen. It's still one scoop, once a day, but now comes with many upgraded probiotics, plus additional vitamins and minerals. I also explored their four human clinical trials to prove out their efficacy, with the data showing a marked boost in healthy gut bacteria. And that's the thing. I appreciate how AG1 keeps adapting to new scientific findings. They have made many formula changes over the years, and each new iteration keeps it at the cutting edge of this space. As I've mentioned, I began my AG1 journey over four years ago. Any company that holds their scientific rigor to the flames of clinical trials means a lot to me. So, subscribe today to try the next gen of AG1. If you use the following link, you'll also get a free bottle of AGD3K2, as well as an AG1 welcome kit, and five of the upgraded AG1 travel packs with your first order. So, make sure to check out drinkag1. com/mat walker. That's drinkag1. com/mat

In 2024, a nationally representative study of more than 1,500 American adults, one of the largest and most carefully designed studies in this space, found that co-sleeping with pets was associated with poorer perceived sleep quality and greater insomnia severity across the entire sample. This was not a study of people who were already struggling with sleep. This was a cross-section of the country, and the effect was driven primarily by dog owners, not cat owners. It was also more pronounced in people with more than one animal in the sleep environment. But, here's the critical caveat I need you to hold in mind. The study could not establish cause and effect. It was a snapshot in time, not a movie. And the researchers themselves raised what is called reverse causation as a genuine alternative explanation. Maybe it's not that the dog is making you sleep poorly. Maybe it's that people who are already struggling to sleep are precisely the ones most likely to pull the dog in close at night. The chronic pain literature speaks to this directly, and I think beautifully. A qualitative study of patients living with chronic pain found that for these people, their dogs were not disrupting their sleep. In fact, they were helping them get to sleep. They were reducing anxiety as bedtime approached, distracting from the relentless cognitive loop of pain anticipation. The physical warmth of another body, a consistent, predictable routine that gave form and shape to nights that might otherwise be formless and dreaded. For someone whose bedroom has become a place of dread of lying awake in the dark, wondering how bad this night will be, a dog can function as something close to a neurological anchor, something real and present that says, in a language older than any word for it, you are not alone in this. Now, what about children? A Canadian research group recruited 188 young people aged 11 to 17 and threw the full arsenal of sleep measurement at them. Standardized questionnaires for both kids and parents, one night of gold standard home polysomnography, and two continuous weeks of wrist actigraphy accompanied by daily sleep diaries. They divided the kids into three groups, those who never co-slept with their pets, those who sometimes did, and those who did so frequently. Then they compared every dimension of sleep they could measure, duration, efficiency, onset latency, number of awakenings, timing, quality. The result was essentially identical across all three groups on every objective measure. Whether you looked at the questionnaires, the actigraphy, or the polysomnography, and polysomnography is the gold standard, and it showed no meaningful difference between children who frequently slept with their pets and those who never did. An interesting caveat though is that the children who co-slept most often with their pets did report the highest subjective sleep quality. A separate study of over 260 No differences by co-sleeping status, age, or gender. For young people, the evidence points toward a verdict of neutral to mildly positive. The furry bedfellow, at least for kids, appears to be doing no measurable harm and may even be doing some subjective good. Over the past 18 months, I've committed to a serious hypertrophy program. My natural body type runs lean. Gaining mass doesn't come easily to me. So, to move the needle, I've had to train with greater intensity, higher volume, and significantly more calories. But with that effort comes a concern I take seriously, which is inflammation, the kind that quietly undermines recovery before you ever feel it. You've heard me say that sleep is the Archimedes lever for bringing inflammation down, and I track mine carefully. But here's the question I had to ask myself. If I hold sleep to that standard, why wouldn't I hold inflammation itself to the same standard? That's why I use Function Health. I also personally know the team behind it, genuinely high-quality people making a genuinely high-quality difference with a genuinely high-quality product. Proud to call them supporters of this podcast and friends. Over 160 lab tests a year

including HS-CRP, vitamin D, and glucose, giving me high-resolution mapping of my inflammation, and so much more. I really could not recommend them more highly. Visit functionhealth. com/mattwalker or use code mattwalker25 for $25 off. That's I have saved the most surprising finding for the end of this episode. We have spent virtually all of our scientific effort asking one question. What does the pet do to the human sleep? It took quite a while for anyone to think to ask the obvious follow-up. What does the human do to the pet sleep? A research group working based in Budapest used a fully non-invasive polysomnography setup to measure the brain activity, eye movements, heart rate, muscle tone, and breathing of nine family dogs while they slept. In one condition, the dog's owner was present in the room sitting quietly. In the other, a friendly, warm, non-threatening human was in the room, but it wasn't their person. Same environment, same temperature, same ambient conditions, just a different human in the chair. The results were unambiguous. With their owner present, dogs fell asleep significantly faster. Their sleep efficiency was significantly higher, and they spent significantly more time in deep, non-rapid eye movement sleep. A friendly stranger could replicate none of this. The owner's presence wasn't just comfortable for the dog. It was, in measurable physiological terms, necessary for the dog's best sleep. And if you want behavioral confirmation in a large, longitudinal study tracking thousands of puppies across the United Kingdom, researchers found that when dogs were simply given overnight access to people, no training, no reward, no coercion, approximately 87% of them chose to position themselves near their human. Not because they were trained to, not for any tangible benefit, because that is, apparently, where a dog wants to be when the lights go out. The bed is a two-way preference. You have chosen the dog. The dog has chosen you. And we now know, for the first time, with polysomnographic certainty, that this mutual preference has a real physiological basis on the animal's side of the equation. You are not just taking comfort from your dog's presence at night. You are genuinely helping your dog sleep. So, what do we do with all of this? Let me close with a few things the evidence actually supports. The practical upshot of 15,000 years of shared sleepings, finally examined under the right instruments. If you are sleeping well and sharing a bed or bedroom with your pet, the research gives you very little reason to change anything. The disruption of sharing the bed is real but modest and largely tolerable for most people. The subjective benefits appear to be real. And apparently, you are giving your dog a meaningfully better night's sleep than they would have without you. That seems like a genuinely good deal. If you are struggling with your sleep and wondering whether your pet is part of the problem, the most evidence-consistent move is not to exile the animal from the room entirely because that removes the potential benefits along with the disruption. The clearer, more measured step is to move them off the mattress. The Mayo Clinic data could not be much clearer. The room preserves satisfactory sleep efficiency. The bed reduces it significantly. A comfortable dog bed in the bedroom a few feet from you is the compromise that the science would endorse. Try it for a few weeks before drawing conclusions. If you have multiple pets in your sleep environment, that could be worth examining. The evidence suggests that the effects compound. One is generally manageable. Three may be a different physiological proposition entirely and the data bears that out. The relationship between number of pets and insomnia severity is not flat. It scales, which is something worth knowing before you decide that a second dog in the bed is just more of the same good thing. One more nuance worth naming. Dogs and cats are not interchangeable in this literature. The negative associations with sleep quality in the large national study were driven almost entirely by dog ownership, not cat ownership. And

separate research found that cats in bed were about as disruptive as human bed partners and associated with less comfort and security than dogs. Cats, as it turns out, are nocturnal by nature in a way that dogs are not. And their circadian misalignment with their owners shows up in the data. So, if disruption is your primary concern and you have a choice in the matter, the species question is not trivial. And finally, if you are someone who sees a sleep specialist or if you are a clinician who works with people who struggle to sleep, there is a question that almost never appears on the intake form, "Is there an animal in your bedroom? " Given that roughly half of all pet owners sleep alongside their animals every night and given that this clearly interacts with sleep in ways we are only beginning to map with proper science, that question deserves to be standard practice. Ask it. The answer might matter more often than you expect. We started this episode with Mara 12,000 years ago sleeping alongside her dog in the cold because it was practical and warm and sensible. We end with a research team in Budapest attaching miniature electrodes to the head of a dog who sleeps more deeply, falls asleep more quickly, and achieves more restorative sleep when its person is in the room. Same ancient relationship, same mutual preference, just considerably better instruments. Thank you so much for listening to today's episode. If you enjoyed, make sure to share the episode with any pet owners you might know. And with that, I'll bid you a good night. Take care for now, and I'll see you in the next episode. — Mhm.