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E38: The Physical Domain of Caffeine

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E38: The Physical Domain of Caffeine

Jan 05, 2024

Caffeine—found in coffee, tea, and soda—is consumed by 80% of the global population. Focusing on the physical domain of caffeine, Dr. Kirtly Jones explores its effects on the human body, its function, and the complex relationship between caffeine and our physical well-being.

Mitch Sears, host and producer of Who Cares About Men's Health, joins this episode of 7 Domains of Women’s Health to share his personal experience with caffeine overdose.


    • Dr. Jones and Mitch Sears explore caffeine's impact on the physical domain, covering its ubiquitous presence, mechanism of action, physiological effects, and associated risks. Through a combination of scientific insights and personal anecdotes, the episode provides a comprehensive overview of caffeine's influence on various aspects of physical health, underscoring the importance of moderation and awareness in navigating caffeine consumption.

    Caffeine's Physical Impact

    • Ubiquity of Caffeine: Dr. Jones highlights the widespread consumption of caffeine globally, with statistics revealing its prevalence in North America and its historical origins in various regions, from tea in the Far East to chocolate in South America.
    • Mechanism of Action: The basic molecular structure of caffeine and its mechanism of action blocks adenosine receptors in the brain, thereby counteracting the neurotransmitter's sleep-inducing effects.
    • Metabolic Boost: Caffeine's ability to increase metabolism, potentially impacting thermogenesis and as an enhancer for physical endurance, particularly in activities like long-distance biking.
    • Muscle Performance: Caffeine's role in improving muscle performance and reducing the perception of exertion during physical activities.

    Risks and Downsides of Caffeine

    • Bone Health Concerns: The association between caffeine consumption and bone loss in older women, particularly when not accompanied by adequate calcium intake, highlights a potential downside of excessive caffeine consumption.
    • Urinary and Gastrointestinal Effects: Caffeine's impact on bladder and gut motility, how it can increase urgency and frequency of urination and promote bowel movements, as well as its potential role in postoperative recovery and opioid use reduction.

    Caffeine Overdose

    • Symptoms and Risks: The symptoms and risks associated with caffeine overdose, including cardiac irritability, irregular heartbeat, and central nervous system overstimulation, emphasize the seriousness of excessive caffeine intake.
    • Personal Anecdote: Mitch shares a personal anecdote about his own experience of inadvertently overdosing on caffeine, underscoring the need for caution and moderation in caffeine consumption.


    • Caffeine's Multifaceted Influence: The complex interplay between caffeine consumption and individual responses recognizes that while some may enjoy caffeine's benefits, others may experience negative effects such as anxiety or jitteriness. 
    • Beyond Caffeine's Physiological Effects: While the discussion primarily centered on caffeine's physical effects, its impact transcends mere bodily reactions. It permeates social interactions, emotional experiences, intellectual endeavors, and even spiritual associations.

    This content was originally produced for audio. Certain elements such as tone, sound effects, and music, may not fully capture the intended experience in textual representation. Therefore, the following transcription has been modified for clarity. We recognize not everyone can access the audio podcast. However, for those who can, we encourage subscribing and listening to the original content for a more engaging and immersive experience.

    All thoughts and opinions expressed by hosts and guests are their own and do not necessarily reflect the views held by the institutions with which they are affiliated.



    Dr. Jones: Are we ready? Yeah, we're ready. We are caffeinated and ready to go. Welcome to the "7 Domains of Women's Health," the caffeine edition. This is the first of the 7 Domains that we will be covering in the world of caffeine, the physical domain.

    If you're listening and drinking something caffeinated, you're in good company. Eighty percent of people in the world consume caffeine in one source or another. And in North America, it's 90%.

    Of course, originally, it was tea in the Far East and in South Asia. And then caffeine spread from North Africa, and chocolate from, well, chocolate, which doesn't have caffeine, it has theobromine, but it's still a stimulant. It came from South America. And colas now are ubiquitous around the globe. So caffeine is part of everybody's life.

    We're going to talk about caffeine, what it is, how it works in the body, and what happens when you take too much.

    Caffeine's Physical Impact

    Now, caffeine is a very simple, small molecule. It works by blocking the effects of adenosine. Adenosine is a small molecule, which is a neurotransmitter, meaning it transmits electrical signals around the body. And it's a molecule found all over the body. Adenosine in the brain works to relax the brain and induce sleepiness, and it builds up when you haven't slept. So it's a little monitor of sleepiness and it makes you feel tired. Caffeine blocks that effect.

    Of course, it has effects all over the body. We will be talking about the cognitive effects when we focus on the intellectual domain in another episode. But here, we'll mention some other body effects.

    Caffeine makes you a little warmer, even if you don't drink it hot. It probably does this by boosting your metabolism. It actually does make your metabolism run a little bit faster. Just a little bit. It won't make up for all the sugar, milk, and cream that you put into it. But it does increase your metabolism a little bit.

    It's used as an enhancer for physical and sports endurance. It delays the onset of muscle fatigue and can keep you going farther and faster for longer. It's often in these special caffeine and sugar gels that long-distance bicyclists like my husband, or more like my brother uses when he's doing a 100-mile bike ride over dirt. It's hard, and sometimes you think you're just going to give up and if you get a little sugar and caffeine boost, you can keep going so you're not dead in the desert.

    It improves muscle performance a little bit. A cup of coffee or tea may give you the emotional and activation energy to get off the couch and go for a walk or to the gym.

    It's also associated with a sense of decreased exertion, meaning when you're caffeinated, you can go farther and harder without thinking you are working farther and harder.

    So people who are asked to get on a treadmill and work as hard as they can until they want to quit and then are caffeinated can work a little harder. Now, music does the same thing, by the way. Music makes you go a little bit harder and faster than you otherwise would.

    Risks and Downsides of Caffeine

    Now caffeine is associated with bone loss in older women. And if you don't drink milk with your coffee or tea, it's a small effect, but it's seen in many studies. So there are some downsides, of course.

    And coffee increases your bladder motility. Most of every woman of a certain age will tell you that their bladder gets activated when they drink caffeine and they have to go pee. Their bladder gets irritable. It wants to pee when your bladder isn't even very full.

    So for people with incontinence and are struggling with urge incontinence, the feeling like your bladder just wants to go when you don't really think you should go, decreasing your caffeine may be helpful because it does increase bladder motility.

    It also increases your gut motility and it makes you poop. It turns out that it may be something other than caffeine in coffee, but it's something in the coffee itself, because when they looked at GI motility when they gave people a cup of coffee and they gave people the same amount of caffeine, people pooped more when they got the coffee than when they got the same amount of caffeine.

    Twenty percent of coffee drinkers report a poop after coffee. And it may happen shortly after coffee, before the caffeine actually kicks in.

    Of course, it could be just something warm in your stomach that stimulates something called the gastrocolic reflex. There's a reflex in your body that when you dump something into your stomach, it increases the motility in your large bowel so you tend to move things along, which is a good thing. You don't want to just keep eating and eating and not move things out of the way.

    Caffeine pills don't really do the same thing. And maybe caffeine colas don't do the same thing either. Most coffee drinkers know this.

    Coffee has been shown to increase gut motility in post-op patients, and it decreases their need for opioid drugs.

    Of course, caffeine withdrawal in post-op patients who aren't getting their morning coffee or tea can lead to withdrawal headaches.

    Caffeine Overdose

    So what about caffeine overdoses? Can you take too much? If it activates almost every part of your body, including your bladder, your brain, your muscles, and your gut, what is such a thing as too much?

    Well, it turns out that too much coffee can really affect your heart. It can make your heart have increased irritability, and it can have irregular heartbeat and irregular rhythm. It can actually cause twitching and difficulty managing a tremor. It can cause central nervous system irritability, confusion, and delirium.

    So consumption of 1,000 to 1,500 milligrams per day . . . A cup of coffee has about 100 milligrams a day or slightly less, so that would be considering 10 cups of coffee to 15 cups of coffee. Or if you're drinking hyper-caffeinated drinks, it may be less than that.

    But consumption of up to 1.5 grams of coffee per day, or 1,000 to 1,500 milligrams, is associated with a condition called caffeinism. So overdose can cause central nervous overstimulation or caffeine intoxication. And it can make people irritable. It can make people have seizures. It can cause people to have cardiac arrhythmias.

    According to the DSM, the Diagnostic and Statistical Manual of Psychological Diseases, caffeine intake in high amounts, over 5 grams, or 5,000 milligrams, may result in caffeine intoxication, including mania, and depression. And it actually has been associated with death. Well, that's a happy thought.

    So caffeine in small amounts can enhance a lot of functions that are good for you, but in larger amounts, it can be a problem.

    And I will say I think I overdosed on caffeine. I was trying to get a little boost in the afternoon while I was watching my granddaughter, and I started munching on chocolate-covered espresso beans. I usually meter them out and think, "I can't eat more than 10." And then I realized I probably ate 30. And it could have been 40. I was kind of sick. I was nauseated. I couldn't eat for a couple of days. And I thought, "Wow, is this what it's all about?"

    So let's talk a little bit about what too much of a good thing can look like. And to do this, in the studio with us, in the virtual studio, we have Mitch. Mitch is one of the hosts of our brother podcast, "Who Cares About Men's Health." And Mitch has a story to tell.

    So, Mitch, I appreciate you moving beyond HIPAA compliance here and sharing with us what happened to you and how you got there.

    Mitch: Yeah, to not bury the lede, I suffered a pretty severe caffeine overdose in college. It was I think junior year, and I was working two jobs. I was taking 18 credits at the time, honors courses.

    Dr. Jones: Oh, no.

    Mitch: I had switched majors. I was trying to do a chemistry and a communication double major.

    Dr. Jones: Wow.

    Mitch: And make it to parties and whatever and ever. And so my solution, because I was young and not as wise as I am these days, was that I would pull a series of all-nighters. It was almost four days of waking up, going to classes, taking finals, going to work, coming home, and writing essays.

    A roommate would walk out and I would be like, "What time is it?" And it's like, "It's 7:00 in the morning." And I'd be like, "Oh, no. I have to get to class." It was day after day after day of that.

    It was this weird rush because I was doing it. I got everything done, right? But at the same time, I was chugging Red Bulls and energy drinks for three, or four days straight. And I was trying to time it just perfectly and drink one at this time, and then, "I'm going to be awake for this many hours and I'll take another one and blah, blah, blah."

    And on the fourth day, I fell asleep afterward. I had gotten everything in, I was done, and I woke up. It was my buddy waking me up. He said that I had been passed out for about 16 hours.

    Dr. Jones: Oh, no.

    Mitch: Yeah. And when I tried to stand up, I was shaking and I couldn't stop shaking. And my heart was going a million miles an hour. He rushed me to an InstaCare and it turned out it was an overdose. It was a severe overdose.

    Dr. Jones: Oh, no. So you'd already been 16 hours from your last dose, as it were, and it still had built up to such a level in your body that you weren't metabolizing it.

    Now, by the way, we talked a little bit, and there are slow metabolizers and there are fast metabolizers from caffeine. But it had been 16 hours and you still were tachycardic, your heart was racing, and you were dizzy. Any other symptoms that you might have had?

    Mitch: Diarrhea. I was in the bathroom the whole time I was in the InstaCare. My face was pretty flushed. I was getting nauseous. I wasn't vomiting, but I was getting really nauseous. And there was a lot of confusion. Lots of love for my sweet roommate who was just like, "You're ridiculous. Let's go take care of you." Yeah, that whole week, I was like, "I’m getting it all done. Look at what's happening, the power and magic of caffeine." And I didn't even think about it.

    Dr. Jones: Wow. And what did they do for you? You can't take a whiff of Narcan or something to reverse like you can a narcotic. What did they tell you?

    Mitch: So they hooked me up to an IV to try to get some fluids in me. My hands and legs were still having these weird shakes and spasms that I couldn't really control. So I think they gave me something like Gabapentin, something to calm down the nervous system. Then they had me take charcoal pills to try to soak up whatever was in my gut.

    Dr. Jones: Oh, even though you hadn't had anything in there for 16 . . .

    Mitch: Yeah, because they were like . . . When I told them that I'd been doing this for four days straight, that's when they were like, "We don't know why you're still like this, but let's do everything we would if someone was actively having . . ." I was there for a couple of hours, and then everything calmed down enough that they sent me home.

    Dr. Jones: If you can think back, how long did it take you before you began to feel like yourself again, or whatever yourself really was back in those days when you were working two jobs and taking a double major in communications and chemistry? When did you get back to whatever yourself was back then?

    Mitch: It took like five days. It took almost a week for me to feel 100% again. It was just like I had shorted out whatever hardwiring of caffeine had happened. I was still having headaches days after. My body felt really weird.

    Dr. Jones: At that point, you might have been having withdrawal headaches. That's the downside, is the withdrawal headache as well.

    Mitch: Probably.

    Dr. Jones: During those four days, were you interested at all in having just a little sip of Red Bull? As they say, the hair of the dog that bit you.

    Mitch: No, I had been spooked enough. There was something about being in an InstaCare, having one doctor after another . . . Because there were two or three of them coming in and they were just like, "How are you still shaking 16 hours later? How are you still experiencing this whatever?" And to have all of that happen and be told it was because I had chugged energy drinks, done the coffee beans through the day just to give me a trickle stream, I was . . .

    Dr. Jones: Well, I did that and it didn't work so well. Yeah.

    Mitch: Afterwards, I swore off the stuff for maybe two, or three weeks, and then I can't stay away from my morning cup of coffee. I abstained for quite a while just because it spooked me.

    Dr. Jones: So your relationship with caffeine now and your relationship with sleep now might be a little bit more measured, would you say?

    Mitch: Yes. So I'm almost 35 now and recently got an ADHD diagnosis. And so I'm on stimulants already. I've been told, "Hey, you can have your morning cup, but recognize your system is already kind of wired up as it is."

    And so I have one really, really good morning cup of coffee, because I always have. It's just this kind of traditional thing for me. I do that one amazing coffee in the day. And then it's really important to get my sleep.

    Dr. Jones: It is really important to get your sleep.

    Mitch: I need that. The idea that I can stay awake for four days straight, I don't know how I did it. I guess it was just the magic of my 20s.

    Dr. Jones: Four days straight. Yeah.

    Mitch: Yeah, maybe getting an hour power nap here or there. But I'm all messed up if I sleep funny these days. I don't know what I was doing in my 20s. Yeah, sleep is really important these days.

    Dr. Jones: Well, that's what they say, is that the brain in adolescence in males doesn't mature until your mid-20s. So you're still an adolescent doing your adolescent thing. Wow.


    Well, Mitch, thank you for sharing that experience. And the word goes out to all of you who are chugging energy drinks, or to those of you like me who just kept eating little chocolate thingies because they were kind of crunchy and yummy and paid the consequences for a couple of days. It was four days before I drank a cup of coffee again. It wasn't a good thing.

    Well, Mitch, thanks for joining us. And of course, you can all hear what Mitch has to say about men's health and life in general at the podcast "Who Cares About Men's Health." Thanks, Mitch.

    Mitch: Thank you so much.

    Dr. Jones: So here we are in the first domain, the physical domain, in the topic of caffeine, with an understanding of how it works in the body, and how it may stimulate in a good way your cognitive function and your pooping, but in a bad way maybe your bladder, and overdosing can be a problem.

    But caffeine is so much more a part of our lives than just the physical domain because it's a big part of our social life. It can be a part of our emotional life. For many of us, it's an intellectual boost. Certainly, there's an environmental impact of the caffeine that we drink, how it's farmed, how it's marketed, how it's shipped around the world, and there is cost to it. And of course, there are spiritual associations with caffeine as well.

    So please listen in to the rest of our little sections on the 7 Domains of Caffeine. It's a big topic, this caffeine one, and we’ve broken it down into the 7 Domains so that you can either listen to all of them, or listen to them bit by bit depending on your schedule and how you can fit it in between your cups of coffee.

    Thanks so much for listening to us on "7 Domains of Women's Health."

    Host: Kirtly Jones, MD

    Guest: Mitch Sears

    Producer: Chloé Nguyễn

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