Do animals recognise when we are feeling the pressure? How can dogs help us when our stress hormones fail? And how has studying stress in horses helped us understand human hormones? Claire Pesterfield, Michelle Sutherland, Dr Clara Wilson and Dr Ruth Morgan let the cat out of the bag as we ask, “Can my pet pick up my stress?”
Hello and welcome to Hormones: The Inside Story, the podcast from the Society for Endocrinology. I'm Dr Sally Le Page, an evolutionary biologist and science presenter, and I'll be chatting with a whole bunch of hormone scientists - or endocrinologists - to bring you surprising stories and cutting edge research from the world inside your body.
In this episode, we're asking the question: can my pet pick up my stress? We'll be finding out all about stress and the hormones behind it...
Ruth: So cortisol is known as the stress hormone, but the most important thing to know about it is it's absolutely essential for life.
Sally: What happens when these hormones fail...
Michelle: I can't deal with any stresses, whether it be happy stress or sad stresses.
Sally: And most importantly, about some very good dogs putting stress to the test...
Clara: Fingal our lurcher when he found the stress, his tail would start wagging because he was like, "I found it, I'm gonna get my cheese."
Sally: We all know life isn't always stress-free. Everyday we face unexpected challenges, whether it be situational pressures from work or relationships, daily annoyances like being stuck in traffic when you *really* need to get there on time, or health challenges like fighting off an infection such as a cold. Fortunately, we have evolved an array of finely-tuned responses to help us deal with the many surprises that come our way, to help us keep our minds and bodies in a healthy state - or, at least, that's the idea.
Sally: And we are not alone in having to manage stress either. Cows get anxious when they're separated from their herd, dogs may become nervous when fireworks go off outside or when they're left alone at home for too long. In fact, pet parents are usually pretty good at identifying when their pet is stressed, but do animals recognise when we are feeling the pressure? And is that a good or a bad thing, both for us, and for them?
Sally: If we're going to untangle these knotty questions, we should probably start with the basics: what is stress, and what do my hormones have to do with it?
Sally: You've probably heard of one of the stress hormones already: adrenaline, the chemical in our bodies responsible for the infamous fight or flight response. Also known as epinephrine, this is what gives you that sudden rushing sensation and sends your heart racing when something exciting or stressful happens - whether it's a fun thing like going down a rollercoaster, or something much less fun, like heading into an exam or being shouted at by your boss.
Sally: But there is a second hormone I'd like you to meet, one that sometimes gets a bad rep but which we cannot live without. Let me introduce you to the hormone at the centre of our story today: cortisol.
Claire: Cortisol is like a stress hormone.
Sally: That's Claire Pesterfield, a medical liaison officer and nurse at the charity Medical Detection Dogs.
Claire: It helps our body respond to stress. And not just the kind of stress we often think about; the emotional stress and things like that, but actually physical stress. So perhaps when our body has been injured or it's unwell, the body will do things inside without us thinking to try and get better. So it has a role in keeping our whole body alive and ticking over, without us having to think about it at all.
Claire: So we need this hormone to actually just function normally day to day.
Sally: Cortisol is one of a group of hormones known as steroids, and it's produced by the adrenal glands: small triangular-shaped organs that sit just above the kidneys. And, as you might have guessed from the name, the adrenal glands also produce adrenaline.
Sally: Adrenaline kicks in within seconds of a stressful event to trigger an immediate fight-or-flight response. Cortisol, on the other hand, acts over several hours, bringing biological backup in the form of changes to blood sugar levels, blood pressure and your immune response, just to name a few of its effects. In this way, cortisol and adrenaline work hand in hand to help the body deal with any surprises life throws at us, whether large or small. Until they don't...
Michelle: Any stresses or illnesses your adrenal gland should kick in. Unfortunately I don't have that, I can't deal with any stresses, whether it be happy stress or sad stresses.
Sally: In 2012, Michelle Sutherland was diagnosed with Addison's disease, a rare adrenal deficiency disorder that causes her stress response to fail.
Michelle: Your body effectively starts to shut down, but quite quickly, your body's going into crisis and you don't have the right hormones to fight whatever sent you into crisis. So then you just pass out and potentially slip into a coma and then, if left untreated, it's fatal.
Sally: Because their adrenal glands fail to release stress hormones when required, people with Addison's disease like Michelle have to give themselves artificial cortisol in order to replicate the stress response their body desperately needs. This means they need to be able to recognise early warning signs to medicate themselves in time. But there's a problem, as Claire explains.
Claire: That's where it gets really difficult because our stress hormones usually give us those warning signs. So if you're not making the stress hormone, you don't get any warning signs to tell you you're getting unwell. So you are very, very sick by the time you actually realise you need help.
Sally: Luckily there's help on hand, in the form of a furry early warning system.
Claire: Medical Detection Dogs is a charity, and we use the amazing sense of smell that our dogs have to be able to detect disease.
Claire: So we will train a dog who's matched to a person with a life-threatening or life-limiting medical condition. And the dog will alert their owner to a change in their health status just before they get really unwell, either to try and prevent them getting unwell or to limit the severity so they can reduce injury or take medication and avoid going into hospital.
Sally: But how can a dog tell if its owner is becoming unwell when the owner themselves doesn't even know it?
Claire: We know a dog's sense of smell is amazing. So you and I can detect a teaspoon of sugar in a cup of tea. A dog's sense of smell can detect a teaspoon of sugar in two Olympic sized swimming pools. So their sense of smell is truly amazing.
Claire: We train each of our dogs for our individual clients. We know that when that person's unwell, their odour for whatever reason changes. And it's that change that we're training our dogs to pick up on. And when the dog notices that, they'll let that person know.
Sally: Unfortunately it takes a lot of time and money to train a dog to perform such a specialist task, so is this something a medical device could do instead? Many diabetes patients now use portable continuous glucose monitors to manage their blood sugar. Couldn't someone with Addison's disease just wear some sort of cortisol monitor to track when a hormone injection is required?
Claire: You are right. There is no need for a dog if the technology is there and it's working. But at the moment, the technology's not there. There is no way of people actually checking their cortisol levels at home. Actually the only immediate identifier that something is wrong is a dog.
Michelle: Come on then. Good boy. Come on then. Yes, yes. Good boy.
Sally: What do you have to say about training as a medical dog?
Michelle: This, what's this? Are you a good boy? Yep, are you a good boy?
Sally: Now, I am not one to pass up on the opportunity to meet a very good dog. And so a few months ago, I travelled to the Medical Detection Dog training centre to meet up with Michelle and her alert pup, Clive, to learn more about how her four-legged companion helps her manage her condition...
Michelle: Back in 2012 I just got a pet dog of my own, and I'd spent a lot of time in hospital. I'd come out and Clive was a young pup at this time. I honestly thought he was the most annoying dog. He would wake me up during the night. He would be obsessed with my mouth. It was really bizarre. Behaviour that was really annoying.
Michelle: But it was only with me. He was not like it was my husband. He didn't wake my husband up during the night. He didn't pester him. He wasn't interested in his mouth.
Sally: This was... not good. Michelle was busy dealing with a new health condition and the last thing she wanted was having to handle a misbehaving hound.
Michelle: I kept pushing him away, but he kept coming back. I thought we'd just somehow inherited the world's most irritating dog. And it was like, I didn't feel very well. So the last thing I wanted was a dog around me and like in my face all the time.
Sally: However, a few months in, a chance encounter changed both of their lives. While visiting a dog show, Michelle came across Dr Claire Guest, CEO and Chief Scientific Officer of Medical Detection Dogs. When she heard about Clive's annoying habits, Claire recognised the signs of an alert dog trying to help by sensing a change in their owner. She recommended that Michelle should start making a record of Clive's antics, and use this information with her health practitioners, to work out whether she needed to take extra steroids
Michelle: And then before you knew, it'd be like, I've actually done a month where we've not been in hospital and my condition is settling down. We're managing that little bit more.
Michelle: And despite me constantly pushing him away at the beginning, he just stuck to his guns and he knew that whatever he was detecting, I could never imagine how we didn't recognise these signs. But yeah, I just thought it was the most annoying pup but clearly he was a clever pup that was just trying to save my life!
Sally: Most medical detection dogs go through rigorous training with experts to make sure they're responding to the right thing. But how did Clive manage to train himself to spot the early warning signs of a problem and alert Michelle all on his own?
Michelle: When we got Clive, I'd not been diagnosed. So I was fit and well.
Michelle: Clive was about 10 months or so, 12 months before I'd got diagnosed. So we kind of think that looking back because Clive had picked up me having like a normal scent to then me not being very well, that my scent is changing throughout the day. That's why we think that Clive was initially picking that up.
Sally: Because Clive showed such promising alerting behaviour, he eventually went on to receive formal training with Medical Detection Dogs...
Michelle: And 18 months later, he fully accredited as an assistance dog for the charity. So that's been our journey. Clive's been alerting me, keeping me out of hospital for the last 11 years.
Michelle: barking
Sally: Addison’s disease can affect people in different ways, some more than others. It’s important to remember that many people with Addison’s live normal lives without any need of a medical detection dog, however, for some people like Michelle, these super sniffer dogs have transformed their lives.
Sally: But how is Clive able to detect when Michelle’s cortisol levels become unhealthy – or how any other detection dogs spot the signs of illness in their owners. Do they recognise a chemical in our sweat? Is it the balance of smelly compounds we breathe out? Is it a change in body language? Something else? All of the above?
Sally: That's a lot of questions to test in one experiment, so let's start with a simple one: do we smell different to dogs when we are under stress?
Sally: Last year, a group of scientists at Queen's University Belfast put this idea to the test. And so I tracked down the lead study author to learn all about the very good dogs she's been working with.
Clara: My name's Clara Wilson. I am a canine behaviour and olfaction researcher, I research dogs specifically how they smell things and how we may be able to utilise that.
Sally: So what is it about a dog's nose that enables it to know so much?
Clara: They have a really large neuroepithelium, which is this area within their nose, and that is the very first step of processing a scent. Roughly dogs have around 30 square inches of this epithelium area, whereas we humans only have about one square inch.
Sally: And not only do dogs have this cool nasal hardware that allows them to pick up scents, they also have the right brain software to analyse it...
Clara: once that smell has been received, it gets sent to the brain, and it gets picked up by the olfactory receptor cells and we have approximately 25 cillia - which is the little hair that's would pick them up - per receptor cell whereas dogs have around 220 million within the nasal cavity.
Sally: Thanks to these amazing adaptations, dogs pick up many scents that we aren't even aware are around us. And they'll notice subtle odour changes that we completely miss.
Clara: In a regular breath sample, it's been estimated that there are between 1,000 and 4,000 different compounds. So you know, for the assistance dogs, their owner just being around them are emitting this kind of melange of smells at all times. But the important thing is if something is to rapidly change, there is a notable shift in that smell.
Sally: Clara and her colleagues decided to test whether psychological stress induced a noticeable shift in someone's niff. And to do this, they needed some dogs...
Clara: They were all very good dogs. We had a lurcher mix. We had a cockapoo, we had a cocker spaniel, and we had a little terrier mixed breed.
Sally: And then they needed some stressed-out humans. In order to get that, they asked 36 people to take a nerve-wracking test - one that might be familiar to many of you listening at home:
Clara: So we followed a very validated protocol that's been replicated a lot in the psychology literature, and it's called a mental arithmetic task, and it involves doing very hard maths.
Sally: That's right, it turns out making people do maths is a well-known and highly reproducible method for inducing psychological stress... Who knew?
Clara: So we had the participants count backwards from 9,000, which sounds straightforward, but they had to do it in chunks of 17. So, you know, 9,000 minus 17, so on and so forth.
Clara: It was amazing how panicked it did get people, because as some people mentioned, it makes them think of school and they're put on the spot, these two people are sitting across from you and looking expectantly at you to come up with the answer, so it was certainly quite stressful...
Sally: Try it at home, it's not easy!
Sally: Here's how the test played out. Before their arithmetic challenge, each participant was asked to collect a breath and sweat sample by breathing on a piece of gauze, wiping it round the back of their neck and sealing it in a small vial.
Sally: They then did the same right after finishing their maths exam, and the resulting samples were presented to the dogs.
Clara: The dog has three options available to them, and the correct option is always present.
Sally: In each lineup, as it were, there would be the person's sample from baseline before they did the mental arithmetic, the same person's breath four minutes later after the mental arithmetic, and what we call a blank, which is just the same material, so the vial and the gauze, but without any breath or sweat on it. The dogs were tested to see if they could sniff out the stressed sample from the other two samples. And how did they do?
Clara: They did really great! They got over 90% correct across all of the testing trials, which is a really impressive performance, and having been with them through training, it was really exciting because they truly did seem to find it quite straightforward.
Sally: Unlike the stressed out participants, it seems Clara's dogs were easily able to complete the task they were given. Clearly, stress has a smell, and the dogs could sniff it out.
Sally: I asked Clara whether we know what caused this shift in odour. Is it a change in cortisol levels? Adrenaline levels? Or something else entirely?
Clara: Oh, that's a hard question to answer. So there are two studies that have shown that there is a compound change in the breath of people before and after doing very similar mental arithmetic or cognitive tasks.
Clara: What was really interesting from this is that they found the biggest discrepancy between the baseline and the stress results five minutes after, but an hour after it had pretty much gone back to being equivalent to baseline.
Clara: And we know from other studies that cortisol peaks around 15 to 30 minutes after finishing a difficult task. And that's really interesting because that's kind of at odds if cortisol was gonna be the main player here.
Sally: So if cortisol peaks half an hour after a stressful event but changes in your breath occur much earlier than that, then the timing doesn't quite line up for cortisol to be the main driver here. Adrenaline, on the other hand, might fit the bill a bit better.
Clara: There are a cascade of hormones that are triggered. Cortisol is often thought of as the main one, but there's actually several others that are elicited from the stress response. However, there's still a big question mark over what's actually going on under the surface. So we simply don't know...
Sally: Dogs are clearly detecting something changing, even if we don't know exactly what, because they will respond to it, even if they haven't had formal training. For Clive, that was his annoying bothering behaviour, but other dogs have been known to predict the onset of a diabetic or epileptic episode by displaying signs of fear like hiding and running under the table, or even getting aggressive. So what's going on there?
Clara: It's possible that if the smell is preceded by your own acting funny or even collapsing or having seizures, you know, that's quite frightening and so that could have inadvertently been negatively associated. So make sure that the dog has appropriate training, finds it a really positive event...
Sally: In other words, you want to associate the target smell with a nice, happy reward so that once trained up, the dog is excited rather than scared when it detects it. Clara noticed it happening in her study too.
Clara: I think that cause our dogs got explicitly trained to approach and smell that odour, they were really excited to find it.
Clara: Fingal our lurcher when he found the stress, his tail would start wagging because he was like, "I found it, I'm gonna get my cheese." So that was very sweet!
Sally: And speaking of "finding the stress", I am well aware that if I find myself around other people who are feeling the pressure, I am pretty likely to pick that up and start feeling anxious myself. So can that happen with dogs too?
Clara: That kind of aspect is called emotional contagion. It is a phenomenon that's seen in group living species. So initially it was thought to predominantly happen within a single species, so dogs and other dogs, but because dogs live so closely with us, this question mark over contagion had been brought up before.
Clara: There was a study previously that collected sweat from people who had watched either joyful or fear-inducing movies and they found that the dogs were more wary around the fear odour, so they were less likely to approach a person when they had this fear odour sample on them. So that suggests this kind of contagion aspect.
Sally: And did the same happen here? Did the dogs quite literally "pick up stress" from the stressed out participant?
Clara: We didn't see any evidence of any kind of contagion in that sense. My hypothesis would be that because the dogs were getting positive reinforcement, so they were getting a piece of food when they found the stress sample, that overrode any kind of contagion that we might have seen otherwise.
Sally: I guess there is nothing the comforting promise of cheese cannot solve - well, if you're Fingal the lurcher at least.
Sally: Beyond emotional contagion, what are the things that make animals stressed out?
Sally: When you and I talk about stress, we often think of work deadlines, financial pressures, moving house, difficult relationships - you know, all of the complications of the human condition. Now, horses don't have mortgages and dogs don't get divorced, but there are still plenty of ways in which animals can be stressed, and unfortunately this stress is all too often caused by human activities.
Sally: Stress isn't just an emotion: it is a physiological state, tightly regulated by changes in our hormone levels. And those hormones are found throughout the animal kingdom:
Ruth: So all animals have glucocorticoids, which is the bigger name for the type of steroid hormone. humans and most mammals have cortisol as their dominant steroid. Rodents and birds have a slightly different one called corticosterone.
Sally: That's Dr Ruth Morgan, a veterinary endocrinologist at the University of Edinburgh, who's studying how stress hormones affect horses.
Ruth: So cortisol is known as the stress hormone, but the most important thing to know about it is it's absolutely essential for life. So it's not always a negative thing. It's a really, really important hormone. So it's a survival hormone basically, rather than a stress hormone maybe.
Ruth: The problem is when cortisol hangs around for too long, because we need it, but we also need it to go away.
Sally: And that, really, is the fundamental principle of endocrinology - because what's true for one hormone is true for them all.
Ruth: Endocrinology about balance. Any hormone that hangs around for too long or isn't there in sufficient quantities, causes problems because it's on a fine balance.
Sally: So when that balance tips, what does stress look like for an animal?
Ruth: For animals, stress is about how your environment changes relative to your needs. And there's a few things that an animal needs. It needs access to food resources, access to water, and for many animals, but not all, social interaction. And so if those three things are disrupted in any way, then that can cause stress.
Ruth: The biggest stressor for many animals is domestication or captivity. So, if an animal doesn't have a choice as to where to find food or where to roam, then that can be very stressful.
Ruth: Animals that are separated from their herd, and prolonged malnutrition. So that could be undernutrition or overnutrition, so obesity or lack of food.
Sally: Most of these make a lot of sense: after all, having no control over where you live or who you interact with is arguably taxing for humans too. So is not having enough to eat.
Sally: Obesity, on the other hand, seems more surprising. Animals aren't exposed to a media environment that promotes unrealistic beauty standards. They don't have to deal with body shaming, discrimination, and all the kinds of societal pressures associated with gaining weight. So why is being obese so stressful for animals?
Ruth: It doesn't make animals stressed necessarily in a psychological way. They don't look in the mirror and think, "I need to get to the gym." What it does is it changes the animal physiologically.
Ruth: Being obese results in a heightened amount of stress hormones, an increased amount of cortisol, whether you are a human or an animal.
Ruth: And there is now an obesity epidemic in dogs, cats, rabbits, snakes and horses because of what we feed them.
Sally: I didn't think I'd seen many obese horses. I usually think of them as athletic and muscley!
Ruth: Pretty sure you definitely have, because around 40% of the horses in the UK are overweight or obese.
Sally: Well I stand corrected...
Ruth: Everybody struggles to slightly recognise obesity in horses because animals can carry fat on the outside, which we often see, but also viscerally so on the inside, just like humans. In horses that results in a condition called laminitis, which is a vascular disease of the feet.
Ruth: And that's really why we have to put horses down. We can't recover their feet, sadly and if they can't walk, it's not compatible with life or high welfare.
Sally: Clearly, imbalanced levels of stress hormones have a severe impact on quality of life for animals and humans alike.
Sally: As both a vet and a hormone researcher, Ruth not only spends a lot of time trying to improve the health of stressed out horses, but she's also looking at what their hormones teach us about stressed out humans too...
Ruth: Studying stress hormones has certainly led to interesting findings when we go back to looking in humans. As a veterinary endocrinologist, I'm always looking both ways; how can I help my own patients and how can I help translationally?
Ruth: So when we looked at horses, we were naive and assumed that horses would metabolise their cortisol the same way humans do, but actually they have a very different profile and they metabolise it in a different way. So when they process cortisol, they turn it into one particular product, and that's called 20-beta-dihydrocortisol.
Sally: It's got a complicated name, but all you need to know about this molecule, or metabolite, is that it's involved in controlling blood pressure. And when Ruth and her team looked more closely, they found it wasn't just restricted to horses.
Ruth: When we went back to look in humans where this metabolite had been described but had been discarded as not important, we found that actually it becomes quite important when people are obese. As people get fatter, they become more like horses in terms of the way they metabolise their stress hormones.
Ruth: And we know that the enzyme that makes this metabolite is found on the 21st chromosome. And so it's in triplicate in people with Down syndrome. So that's really important to give an insight into how people with Down syndrome might process their stress hormones and if that can give us any clues as to how they respond to stresses.
Sally: So can our pets pick up our stress? Well, it certainly seems so.
Sally: Dogs can smell stress on us after a tough maths exam or a scary film. Some animals, like Clive the cocker spaniel, can tell when our stress hormones aren't working as they should. And we might even be adding stress into their lives by giving our pets too much food.
Sally: There is so much we can learn from the animal kingdom, from understanding how our stress hormones work...
Ruth: I think it highlights that our work in horses not only helps horses, but it can help humans.
Sally: To training a detection dog to alert when our stress hormones don't work...
Michelle: I actually didn't believe a dog could do what Medical Detection Dogs said they could do, I never believed it was ever possible. But I take it all back because it clearly is, and my life is very different now. Just incredible.
Sally: That's all for now. Thank you to all our guests; Dr Clara Wilson, Dr Ruth Morgan, Michelle Sunderland, Claire Pesterfield and the rest of the Medical Detection Dogs team.
Sally: Next time, we'll be asking, "Is my diabetes my fault?". We'll be delving into genetics...
Ines: So around 40% of your risk of developing type 2 diabetes comes from your genes.
Sally: Learn how pregnancy messes with our blood sugar levels...
Lorna: Insulin resistance is something that actually just occurs in all pregnancies, including healthy pregnancies.
Sally: And why type 2 diabetes is a much more complicated disease than we realise
Shivani: How can people all be labelled with type 2 diabetes and be presenting completely differently ?
Sally: Hormones: The Inside Story is a podcast from the Society for Endocrinology. Explore more about the world of hormones at yourhormones.info and follow them on twitter @your_hormones
The show is a First Create the Media production. It was researched, written and produced by me, Sally Le Page and Emma Werner. Our executive producer is Kat Arney. Thank you for listening and we'll see you again soon.
References:
Dogs can discriminate between human baseline and psychological stress condition odours
Interspecies transmission of emotional information via chemosignals: from humans to dogs (Canis lupus familiaris)
