Good Stress and Bad Stress: Measurement in a world of wearables

And I think that stepping back to think what are sort of the puzzle pieces that we as scientists are still putting together, I think that's really useful for consumers to be able to have the tools and kind of this common language, to make informed decisions, to feel better about talking with other people about these topics. And also, I have a little bit more on like the human side of who is doing this science.

Welcome to The Stress Puzzle, where we explore the latest in stress science and consider how the science may translate to our daily lives, or where we might have missing pieces for actually

making that connection. I'm your host, Ryan Brown, and I'm a social health psychologist working with the Stress Measurement Network, which is a team funded by the National Institute on Aging and includes internationally recognized stress experts from UCSF, UCLA and Yale in today's episode, I'm joined by the directors of the stress measurement network, Drs

Elissa Epel and Wendy Berry Mendes. We talk about the purpose of the network, the importance of distinguishing between stressor exposure and stress responses, the role of wearables and their limitations, and what's ahead in the first season of the podcast. So as we dive into The Stress Puzzle, the first thing to point out is how we really often use the word stress to mean so many

different things. We use it to refer to chronic stress, not having enough money to cover rent, having a sick family member working in a toxic environment, and how this might create excessive wear and tear on our biological systems and make us sick. But we also use stress to mean the stress that we experience before an important interview or having to give a public speech. And this type of stress is acute stress

and a completely different beast. So I'm really thrilled to be joined today by two experts, one who studies chronic stress and the other who studies acute stress. Dr Elissa Epel has focused on linking chronic stress to health, and Dr Wendy Berry Mendes is an expert who is focused on characterizing acute stress responses. They've been working together for over 10 years and have been co leading the NIH Stress Network. Elissa and Wendy, welcome to the podcast.

processes. She's also a beloved mentor to so many researchers, including me, and we're really fortunate to have her as a co director of the stress measurement network. We're also joined by Dr Wendy Berry Mendes, the Dilley professor in the

response. Her research on stress often goes beyond thinking about the individual to characterize how one person's stress impacts another person's emotions and physiology. It's really cutting edge and fascinating work. She's incredibly creative, impactful, and we're so lucky to have her as a co director of the Stress

Measurement Network. So I wondered if y'all could start off by giving us an explanation and just a little bit of the background around why the National Institutes of Health will fund networks like the Stress Measurement Network. the future direction of the field. We get to do that in smaller groups, but not at a national level. So societies can do that. Funders can do that. They help set the agenda for scientific progress and identify gaps and priorities and

networks. Do that in a very focused way. They also provide a service to the field and identify ways that the field needs curating and support. So stress was exactly one of these areas. It just wasn't progressing. And so many institutes at NIH wanted to explore the role of stress, but noticed that scientists from different disciplines weren't even talking about stress in a unified way and not and they

weren't agreeing on how to measure stress. So the gaps and the need for some harmonization of the field and some bringing together researchers to have common definitions, taxonomies, measures, was so apparent to our behavioral scientist colleagues at NIH particularly NIA and so we were excited that they have prioritized the Stress Network.

science and the measurement of stress. So we reach out as a network to many people across many different fields, in an attempt to learn from all the different disciplines about stress science, to harmonize, like Elissa just mentioned, and to develop interventions to eventually influence public policy. So a network has different goals that are broader and across multiple disciplines.

initiatives. It is such a broad focus to advance the science of stress that is not from an individual lab university, but is really being motivated by experts across the country and internationally in the needs for their particular niches within stress science. Because, like we were saying, even though we like to call a lot of things stress, there's a lot of important nuance and different ways that we can look at these questions.

I think that what y'all are pointing to is how the network really allows us to capitalize on a lot of different people's expertise and also enables a better sense of community, I think, among folks who are interested in these questions, moving to the stress measurement network. Specifically, what is the exact purpose of this network?

or acute stress. So the purpose of this network was to try to push forward this stress science by developing initiatives to fund novel research that would potentially increase our ability to measure stress in daily lives. Look at interventions that would help people manage their stress and eventually influence, potentially influence public policy.

doesn't happen in a vacuum. It unfolds in a very specific way in social context. So it really reflects both what's happening in the social and physical environment and what the person is bringing to it in terms of their life experience and expectations and automatic mental filters. So there's so much that goes into the stress response that we're we're always learning and getting better at predicting and understanding

biological stress responses. I love what Sapolsky said many years ago, which is that stress is so unique in particular, in any one moment, it's like a signature, a personal stress signature.

And we give them a scale, and they are able to say some number that represents how stressed they feel, and we can measure changes in the body or basal levels of of what we think of as like stress systems, and one of the head scratching moments for all of us is how low that correlation is between what people say they feel in terms of the stress that they're experiencing and their body's stress accumulation. Now, why is

that? Why aren't people able to report on a stress that matches their body, or why isn't the body sort of in lockstep keeping up with and reflecting how people feel? And one could say, well, it's a problem with your subjective report, but also could be a problem with the biology, but that discrepancy between our psychological experience and our biological

response is a real puzzle for stress science. So one of my favorite but but depressing meta analytic findings that was reported in literature is that cortisol, the hormone that people will call the stress hormone, is not correlated. Basically, has a meta analytic correlation of negative point, oh two, with people's experience of stress. Now that, to me, is the best example that there is a puzzle here with the subjective experience of stress and how your body responds to it.

of these problems. And I think that stepping back to think what are sort of the puzzle pieces that we as scientists are still putting together, I think that's really useful for consumers to be able to have the tools and kind of this common language, to make informed decisions, to feel better about talking with other people about these topics, and also have a little bit more on,

like the human side of who is doing this science. So I really hope that this podcast can be helpful for anyone listening, and then, if you're a researcher, we want to highlight the nuances of measurement and interpretation. And we'll also be doing some more deep dives into specific resources that we offer to support grant and even paper writing as well as, you

know, stress measurement, network leadership. I would love to know what you hope people will gain from these future episodes of the stress puzzle.

it should be frustrating. You should keep you up at night so that your speakers convey that. And it is, it is an area and a topic worthy of trying to figure out

That's something that I really hope that we can emphasize throughout these episodes, and maybe even in some special episodes, to give you a really full picture of what might not even be available in the published literature, but each of our guests has such a wealth of knowledge that I really am excited to tap that for everyone who might be listening and folks who are listening with lived experience as well. We want to

hear from you. We definitely want this to be a two way street of thinking about stress from the researcher perspective, from the lived experience perspective, and how we can most accurately and impactfully translate the research into policy and practice in a way that really helps people's lives. So that's what I'm really excited about. Getting into these episodes

to interpret for them how stressful their day was. And so people are getting messages of you had a very high stress day, but they don't necessarily feel subjective stress, and in fact, the high readouts of autonomic arousal often reflect socializing activity, these other factors that we just can't

seem to get rid of yet in our algorithms. So it's a really amazing time to educate the public at large that physiological stress is not the same thing as subjective stress, and that goes toward the acute stress response as well, that we may be responding to a stressor in our environment and our body may be responding, and we may be reporting very low levels of perceived stress or threat. So this is part of the puzzle, is understanding well which which channel matters. Do they both

matter? Do algorithms of levels of emotional responses, cognitive appraisals and physiological responses matter? The stress response is so multi dimensional and complex,

response. In some way your body is betraying you, and it means you're really nervous. If I gave you the idea that, look, you know, stress and how your body responds to something that's important, you should think of a lot like physical exercise, right? If you were on a treadmill and you really wanted to get a great workout, you might run harder and your heart would beat faster, and there's no way you would interpret that as negative, right? Because it's about getting oxygenated blood

out to your muscles. Well, in the same way, when you're doing something cognitive that has a high motivational impact, you want to do well your body is going to respond, and it needs that oxygenated blood out to your brain, out to your muscles, to perform better. So back to that interview, walking in with a pounding heart rate could help you perform better now. It also

could undermine you. It could make you, you know, stuttering, your words make you freeze and not remember the details that you wanted to remember, but the difference in the physiological responses that you have that would be basically a good stress response for versus a bad stress response is not going to rely on something that's just your heart rate. There's lots of changes in

your body. Some of these changes are going to help you perform better, and some are going to help, or basically undermine your performance and and be part of a worse outcome, teaching people when their body is responding positively and adaptively, and how to harness that, versus the times that your body portrays you and actually undermines your performance, is a really exciting future direction of wearables that could help you potentially harness those two different responses.

There's one more distinction that's so obvious that we're at risk of not bringing it up, that is stressors versus stress

responses. So Lis Nielsen, who is the director of the Behavioral and Social Research Division at NIA, has been talking with researchers across disciplines about stress, and has been frustrated that even that very fundamental difference between calling events and exposures stress and subjective stress responses, stress is happening all over and it's such an easy clarification to say, let's be really specific when we're defining our terms and our independent variables, and yet,

we, even as stress researchers, so easily, use the word stress, which is almost meaningless. So stressors, our stress toolbox, on our Stress Network website, has so many great and validated measures of different types of exposures, events, chronic stressors, types of environments, neighborhood stressors that we are exposed to, and it also has measures of subjective response and so, and some measures mix up the two.

And so we can't really inherently separate them so easily, but it's just, we've just got to start there and say, let's get better at talking about exposures versus responses.

about what information these platforms really have. Do they have, the context of, were you exercising or not even and that can give you a better idea of how well they are characterizing any individual response that you might be having, because if they don't have that broader context, then they're really just pulling from these physiological signals that might be due to a variety of contexts.

just the opposite. So there's going to be a need for a lot of contextualizing and understanding what a physiological response means that is read out by these different wearables. But I will say I am excited about potentially people getting more information from wearables, because I also think it could work almost like a scale for somebody who might be monitoring their weight. And of course, how much you weigh does not mean in any way that it's, you know,

directly tied to health. But say that one wanted to use their weight as, like, a crude measure of their health, a scale gives you a sense of, like, you know, how am I doing? Am I exercising enough? How am I eating? And you could monitor it and sort of see how you're doing over a week or a month or a couple months, in the same way, using wearables to get insight into things like heart rate variability, something that most people don't really understand what their heart rate variability should

be, but I'll tell you that high is good and low is bad. But blood pressure, which we do have a better sense of a lot of the wearables now are trying to move toward blood pressure, knowing what your blood pressure is when you wake up right before you're about to go to sleep at night, what it looks like a half an

hour after exercise versus two hours after exercise. Using that information gets one more in touch with how their bodies respond, how it's progressing over time, and if one is trying to potentially get healthier and maybe lower their blood pressure a bit, these wearables could potentially help them do that by giving them basically in the moment, feedback of when there are times that their blood pressure is lower, and try to optimize those times.

physiology changes over the day, and how they sleep. And so now we have the window into, at least with autonomic nervous system and sleep, into how people are changing based on their day, on stressful events, on positive events, on their motion regulation. And so we have learned. So much more about stress and the nervous system in the last 10 years from these

daily studies and these biosensors. So the field has really shifted away from these self report measures that that they do capture important exposures and responses, but these trait measures are clearly not the best way to measure intervention changes or to understand the real within person, daily dynamics of stress and health.

actionable research into ideal times to intervene as well. So I totally hear what you're saying there, Elissa, what really strikes me about for both of you is one how prolific, obviously you both are in the research world, but also how you've maintained your curiosity and engagement and just dedication to mentorship and so, so it makes me want to take a step back and ask you both, what was the spark that got you into stress research to begin with, and sort of, what have you loved

the most at first, and what are you most interested in now.

important, like a performance. And so I think I was drawn to the idea that my body could recruit this metabolic energy, and that energy could help me perform better, right that high of a performance when you are ready and you're excited and you're prepared, but those same physiological responses could do just the opposite when you're not prepared, when you feel like you're not ready for a role or somebody's really important in

the audience that you don't want to disappoint. So I think I was always drawn to that idea of how your body responds to these important moments in your life. And so I think I was just

naturally drawn to stress science. When I started studying physiological responses and emotions and stress, I was also drawn to this idea that people don't always report what they actually believe, and that bodily responses can give you a window into what people might be unwilling or unable to tell you, and that came from work when I was looking at people interacting with others who they were more unfamiliar with, who might be from different social groups, and people often would

report enjoying an interaction, but then their body would suggest that they were more awkward or unsettled, and so I've always been interested in both that discrepancy and how your body responds. And then now I'm really excited. You know, we're talking a lot about wearables, but you know this huge benefit is that you're getting people's responses in their daily life. And as great as a lab study is with all of its controls, and it's very careful and rigorous

manipulation. What a researcher wants to understand often is how people respond when it's critically important to them, and you know, interacting with the spouse or having to talk to your boss those moments in life that are really critical, these wearables could give us insight into those. So I'm really excited about this next generation of being able to measure the body in real time and delivering interventions in real time to help people manage their stress.

because everybody before stress experience gets sweaty. But if you're cold and sweaty, it means you're vasoconstricting and so probably having less blood going out to your muscles and to your brain, you might be having a more negative stress response, but if you're hot and sweaty, that means that you're having a more positive or adaptive stress response. So I do seek out my students and close colleagues and try to hold their hand before a stressful task.

of exposures and presenting safety signals. You know, one of our recent papers by Alexandra Croswell, really points out that we need to consciously and effortfully look at what makes us feel safe and supported for our nervous system, because stress may be the default, and this is something our stress network has talked about a lot. Is new models of stress? What

are new theories of stress? And how can we, rather than just thinking of looking for stress in the midst of acute stress, what about looking for how much someone holds on to stress when nothing has happened, when they're having a resting baseline? This idea of, can we change our rest and baseline through meditation or other Mind Body practices. So that was my interest going in. And really, I would say, understanding the stress physiology from the cellular level to the nervous

system has just remained a fascination. We're still learning more about understanding the human stress response and how that's relevant to development, reproductive, development and aging. So at the beginning, there was very little research on the acute stress response in a standardized way

and ways that we could look inside. And so way back when we were in graduate school, these acute stress studies were just starting to blossom, and particularly from the trier group, Dirk Hellhammer and Clemens Kirschbaum, they were identifying the boundary conditions and the parameters of

what stresses people out. In the lab, can we make a standardized protocol, what is the normative cortisol response and, to some extent, autonomic response, and just mapping that out opened this whole world of trying to understand the HPA Axis response to an acute social stressor. So one by one, these studies were coming out, and that was when I was entering the field and realizing how much we could learn with lab studies and looking at salivary cortisol trajectories, and even upon

wakening. Now, you can't even keep up with that field because it's so large, but at the very beginning, each study that comes out increases our knowledge in the field, you know, by by a huge amount. So it was the same for when I started studying this relationship between stress and abdominal fat. There was a few rat studies, there were a few correlational human studies. So it was so exciting to see not just what our studies found, but what other people were finding across the world. Same with

telomeres. We did one of the first stress telomere studies, and then was so exciting to watch as the field evolved and other studies popped up in other parts of the world linking telomeres to some aspect of stress or mental health. And again. Now I can't keep up, so it's very it's exciting to be at the beginning when you can read every study in detail, and then the field really moves on. So now we're deep into social genomics like epigenetic clocks, and boy, is that field moving

fast. Hold on to your seat, because what you what study today is going to, you know, change next year. So that's been really keeping up my my curiosity and wonder at how quickly we learn and how we can put together the story of stress from, you know, from cell to society.

called. My BP lab, and we had hundreds of 1000s of people from all over the world measuring their blood pressure and their sleep and their stress and emotion in everyday life. And we looked at some data that showed really compellingly that when people slept less than they typically sleep. So these were daily responses that were tracking people's sleep every day and then their morning blood pressure. And for any person, when they slept less than their average, their blood pressure

was higher in the morning. And when they slept at their average, or more than their average, greater than their average, their blood pressure was lower, and that happened until you hit about, you know, seven to eight hours a night, and then blood pressure stayed pretty flat, and I used to be somebody who convinced myself that I didn't really need seven or eight hours of sleep. I was one of those people who would try to convince myself I could just make it through on caffeine

alone. And I saw those data, and I changed my behavior, and now I well at least seven hours of sleep. I seven hours every night. I I demanded of myself. I change my my traveling so that I don't ever get less than seven hours of sleep, because morning blood pressure, especially is so critical for good health, you want to start the day with your Nadir waking blood pressure, lowest levels. So that was really impactful for me.

social stress of living in an unsafe area. So getting better at measuring the specificity of the different types of social stressors that people are experiencing that we think are drivers of stress related aging and early disease is an area that we are fully in right now, and we welcome researchers to

send us different measures that they have created or studied. So we are sharing established measures, but we are also very interested in works in progress, in measures that have been tested enough to share the scale as a measure under development. Now my personal focus is really on trying to understand at a more mechanistic level how chronic stress can create

accelerated aging. And it's always going to be interesting to study the actual stress response systems, HPA axis, autonomic nervous system, and how they look when they adapt to different types of chronic stress. But one of the more fruitful directions may be understanding that the mechanisms of how stress causes disease at the cellular level.

So for example, there is a lot of emerging research on understanding mitochondria energy dynamics as a basis for understanding stress effects and how they create the whole syndrome of aging and changes in different organ systems and regulatory systems. So getting down to fundamentals with omics, and particularly with mitochondria, like the work of Martin Picard is going to be a very fruitful direction for us.

from the body to deliver stress interventions just in time. It's a it's a label that means so as somebody was getting more stressed, and maybe at some pivotal moment, being able to deliver some stress management tool, whether that's listening to relaxing music, encouraging them to engage in paced breathing, or doing some offering some psychological intervention to help people manage their stress, or at least harness it in a way that might be more beneficial. So I think

stress interventions is really exciting. I think another area is looking at stress, not just at the individual level, but in dyads and families and groups. So our emotions, motivation, our stress responses don't just live in us, they emanate from us and influence people around us. And imagine the last time that you were with a friend, maybe who was really anxious or nervous about something, you might have even picked up on that and felt it yourself. You're now it starts shaping your own stress

response. And I think the idea of looking at stress, not just how it affects an individual, but in the wider community that you live in, and us understanding those dynamics. How do communities experience stress? So we can potentially intervene at a system level. I also think we need to do some good work on unmeasuring stress. I mean, back to them, was the first sentence that we said, Ryan, which is, how do people

experience stress? Can we get better at measuring it, and can we help people label and identify the experiences that they're having to better and more accurately label what they're feeling. Maybe somebody is just feeling unsettled, or maybe they're excited, or maybe they're dreading, but the more accurate and precise your labels are may potentially help you

resolve those feelings better. So I think giving people a better language to talk about stress is a really exciting future direction as well.

work and really advancing work that can inform policy. And when you're talking about those stress interventions, I think it's especially exciting to imagine the kind of just in time interventions that could be supported in this world of telehealth and where folks have really limited access to mental

health resources. That really stands out to me as a service, that this kind of research and this kind of access to technology can actually impact people's lives when they're further away from, you know, a clinically trained psychologist or something like that. That gets me really excited as well. So I'm really glad you touched on on that piece.