How Your Morning Coffee Affects Your Brain, Gut & Nervous System

How does coffee and caffeine affect the body?

In this episode of Health Recoded, we break down the science behind caffeine, coffee, and how your morning coffee affects the brain, gut, nervous system, hormones, anxiety, sleep, and overall health.

If you’ve been experiencing anxiety after coffee, gut issues, jitters, fatigue, poor sleep, appetite changes, or feeling overstimulated after caffeine, this episode will help you understand what is happening physiologically inside the body.

Many people don’t realize that caffeine affects nearly every major system in the body, including:
the nervous system
cortisol and stress hormones
gut function and digestion
sleep and recovery
mood and anxiety
appetite and metabolism

In this episode, we explain the anatomy and physiology behind caffeine, what happens when you drink coffee on an empty stomach, how caffeine interacts with stress physiology, and practical nursing perspectives on safe daily caffeine intake.

We cover:
How caffeine affects the brain and nervous system
Adenosine, dopamine, and caffeine physiology
How caffeine increases cortisol and stress signaling
Why coffee can worsen anxiety and overstimulation
Why coffee affects digestion and bowel movements
Coffee, appetite suppression, and blood glucose changes
How caffeine impacts sleep and recovery
Safe daily caffeine intake recommendations
Common myths and misconceptions about coffee
Practical tips for healthier caffeine consumption

If you’re looking to improve your energy, nervous system regulation, gut health, sleep, or relationship with caffeine, this episode gives you a science-based and approachable place to start.

Subscribe for more conversations that help you better understand your body, physiology, and health. New episodes weekly.

Chapters:
00:00 Intro
00:26 Daily caffeine intake
01:42 How does caffeine affect the body?
03:30 Does caffeine increase cortisol?
04:45 Does caffeine cause anxiety?
05:59 Is caffeine addictive?
07:21 Does caffeine cause fatigue?
08:29 Why does coffee make you poop?
10:44 Does caffeine suppress appetite?
12:53 Does coffee worsen sleep?
15:00 Common misconceptions about coffee
17:25 Nursing tips for daily caffeine intake
22:23 Key Takeaways

This content is for educational and informational purposes only and is not a substitute for guidance provided by your own medical professional.

Resources:
Coffee & Health — Debunking Coffee Myths
https://www.coffeeandhealth.org/health/media-content/information-campaign/debunking-coffee-myths-the-truth-behind-your-brew
National Institutes of Health — Caffeine Overview
https://www.ncbi.nlm.nih.gov/books/NBK223808/
FDA — How Much Caffeine Is Too Much?
https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much
Sleep Foundation — Caffeine and Sleep
https://www.sleepfoundation.org/nutrition/caffeine-and-sleep
Harvard T.H. Chan School of Public Health — Coffee
https://nutritionsource.hsph.harvard.edu/food-features/coffee/
American Academy of Sleep Medicine — Caffeine Effects on Sleep
https://sleepeducation.org/sleep-disorders/caffeine-and-sleep/
Temple, J. L., et al. (2017). The Safety of Ingested Caffeine: A Comprehensive Review
https://pubmed.ncbi.nlm.nih.gov/28675917/
Glade, M. J. (2010). Caffeine — Not Just a Stimulant
https://pubmed.ncbi.nlm.nih.gov/20182054/
Nehlig, A. (2010). Is Caffeine a Cognitive Enhancer?
https://pubmed.ncbi.nlm.nih.gov/20182035/
Fredholm, B. B., et al. (1999). Actions of Caffeine in the Brain
https://pubmed.ncbi.nlm.nih.gov/10484644/

Transcript

SPEAKER_00 0:00

Your morning coffee may be making you more tired than less. Let's talk about why. Hi, I'm Alex. I'm your nurse, and today we're talking about how coffee, caffeine more specifically, affects the body. This is not to ostracize coffee or tell you that you can't drink it or to tell you to stop drinking caffeine as a whole, but it is important. There is some nuance to knowing how it affects the body. So let's talk about it and see what it does. As of 2026, roughly two-thirds of American adults drink coffee daily, with the average coffee drinker consuming approximately three cups per day. Daily caffeine intake is roughly 400 milligrams of caffeine per day. That's the recommended amount to not go over. And this is roughly four eight-ounce cups of brewed coffee, ten cans of cola, or two energy shot drinks. So on average, three cups per day. Most people are eating underneath or within the daily limit for caffeine intake. But there's lots of new beverages that are coming out, particularly with caffeine in them, and many of them go above that recommended amount. Many new drinks exceed 200 milligrams of caffeine per serving, with some reaching up to 16% more than what is advertised on the label. Coffee and caffeine interact with your nervous system, your hormones, digestion, and your stress physiology, especially when it's administered first thing in the morning or ingested first thing in the morning. This is not to ostracize your daily coffee. I'm not going to tell you to stop drinking it again. This is just to discuss how caffeine affects the body so we can make the best decisions for our health. How does caffeine affect the body and your health? The foundational physiology. Caffeine is a central nervous system stimulant that primarily works by blocking adenosine receptors in the brain. Normally, adenosine builds throughout the day as the body uses energy, and this increases increasing adenosine levels contribute to fatigue, slower neural or brain activity, sleep pressure, and relaxation. Caffeine structurally resembles adenosine, allowing it to bind to adenosine receptors without activating them. So this temporarily reduces the perception of fatigue and increases alertness. Importantly though, caffeine does not create energy. It alters signaling related to fatigue perception and nervous system activation. So the focus effects, adenosine builds throughout the day and creates sleep pressure and fatigue. So it builds up so that at night you'll fall asleep. Caffeine blocks adenosine receptors temporarily. So you don't become less tired, you become less able to perceive the fatigue. So coffee or caffeine blocks fatigue. It doesn't necessarily fix it. And a lot of people are drinking coffee instead of actually listening to their body's signals of fatigue. So caffeine competitively blocks adenosine receptors, particularly A1 and A2A receptors. This leads to increased neural firing, increased alertness, and reduced fatigue perception. So once caffeine wears off, adenosine can bind again, contributing to that crash that you experience. Coffee doesn't create energy, it just changes how your body perceives fatigue. So then this moves into cortisol. Caffeine stimulates the HPA axis. Hypothalamus, pituitary, and adrenal glands are in this axis. And these all work together, but ultimately this will increase cortisol. So cortisol naturally rises in the morning, and this is your cortisol awakening response. So caffeine or coffee in the morning after you wake up can amplify this alertness, the sympathetic activation, so you're feeling more awake, and then stress signaling as well. And for some people that's fine, but for others, this will feel like increased anxiety, palpitations, dysregulation, or shakiness, especially if it's taken on an empty stomach with poor sleep or with a higher baseline of stress. So, like for me, I can't take caffeine. I can't have much more than maybe 40 or 60 milligrams that comes from a cup of tea because I feel like I'm going to have coronary if I have caffeine. And it doesn't affect some people that way. It genuinely they'll have 200 plus milligrams a day and they're functioning fine. That's their normal, that's their baseline. It just affects me differently. So maybe you're one of the ones that's a little bit more sensitive to it, and maybe you're one of the ones that's not. But ultimately, this is how it's working, no matter if you're sensitive to it or not. So caffeine can increase catecholamines and central nervous system stimulation. So this can lead to anxiety and mood and situations like that. So that's what we're talking about here. Coffee can improve alertness and your mood and also dopamine signaling, but in susceptible individuals, high caffeine intake can worsen anxiety, palpitations, panic symptoms, restlessness, all these things that we talked about. Physiologically, caffeine can mimic sensations associated with anxiety, therefore making the person actually anxious. So this is why some individuals experience significant nervous system dysregulation with caffeine, particularly when taken on an empty stomach or if you're already in a stress response. It's causing your physiology to also be more activated, just like your brain is. Or maybe you were perfectly calm and fine before, but then you start feeling like you're stressed and anxious, like it starts feeling like those same, um, that same process, even if there's not a stimulus, and then you'll actually start to get anxious. So talking about the nervous system, is caffeine addictive? Caffeine can produce dependence, but it's more of the dependence on the effects, but there is some physiology behind this. So with regular intake, the brain adapts by increasing adenosine receptor sensitivity and density. This contributes to a tolerance, meaning you're gonna need more doses later after you've built up this tolerance in order to get the same effect. When caffeine is removed abruptly, adenosine signaling rebounds. This is part of why you get a headache when you stop taking caffeine daily or when you maybe have missed your typical intake within that day. This can cause withdrawal symptoms such as a headache, fatigue, irritability, difficulty concentrating. Caffeine dependence is recognized clinically, although it differs from more severe addictive substances. Ultimately, most people consume caffeine habitually because it temporarily improves alertness and energy perception. But if you decide to stop, you may need to wean yourself off or just know that you're not gonna feel great for a little bit as you come off of it. And that's expected. So your nervous system experiences caffeine as stimulation. Caffeine stimulates adrenaline, dopamine, and central nervous system activation. So you'll maybe experience increased heart rate or increased blood pressure. So the body is shifting toward a more mobilized physiological state. And this can be useful for performance or waking up or exercise, but excessive stimulation can contribute to nervous system fatigue, poor recovery, or just chronic stress signaling overall, especially when it's combined with poor recovery, poor sleep, increased psychological stress, or under-eating. You're not supporting your baseline physiology, and so the response that the caffeine is giving you is so much more. So potential symptoms can include an increased heart rate, sweating, jitteriness, anxious sensations or thoughts, and this is particularly relevant in dysregulated nervous systems. If coffee makes you anxious, shaky, or crash later, your body may be telling you something, and it's typically not that you need more. So, talking about the GI tract, I don't think this will surprise anybody, but coffee does stimulate colon motility, GI contractions, and gastric acid secretion. Coffee also stimulates the production of certain hormones that then stimulate digestion and bowel contractions further. So this is why many people have to poop or go to the bathroom after having coffee. Coffee on an empty stomach can worsen nausea, reflux, GI irritation, and then also cortisol and stress response in sensitive people. Another point that I wanted to make with the GI tract and caffeine, particularly coffee, when taken in the morning on an empty stomach, it can really change the absorption of certain supplements and your food. So it can reduce the absorption of iron, calcium, and magnesium specifically, especially when consumed without eating. Talking about these more specifically, iron, polyphenols, and tannins in coffee can reduce the non-heme iron absorption by binding iron within the GI tract. So this is most relevant in those with iron deficiency or menstruating women, and then people with low dietary iron intake. So ultimately, this usually does not create a deficiency in healthy individuals alone, particularly with adequate supplementation and nutrition, but it is something to pay attention to. If you're needing to supplement or you already have low iron, you may want to pay attention to the timing of your coffee in the morning and when it's on an empty stomach. Talking about magnesium, you may need more supplementation with magnesium. We're going to talk about this in a second. Coffee can be kind of dehydrating because it stimulates everything to work a little bit more, so you're flushing more out. Again, we'll get into it in a second, but essentially, this could help to excrete more magnesium from your body, particularly through your kidneys. And as a result, you may need to increase your magnesium intake if you consume regular amounts of coffee, particularly in the morning, but caffeine in general throughout the day. Talking about appetite changes and blood glucose control when consuming coffee, coffee can blunt your appetite temporarily, and it'll also alter glucose regulation in some individuals, and this can contribute to crashes later, particularly if you're underfed. So coffee and fasting plus stress and poor sleep, this can create a very dysregulated morning physiological state in your body. So this is why we want to make sure that we're ideally taking in food with coffee, and even if it's not at the same time, it's within a certain time frame so that the body isn't just digesting only this increased stimulant, essentially. So, how does this affect blood glucose effects? Caffeine increases catecholamines, and again, this is adrenaline and noradrenaline, and these hormones stimulate glycogen breakdown, glucose release into the bloodstream, and this temporarily increases blood glucose and then reduces insulin sensitivity acutely. Okay, so as a result, your blood sugar may go up a little bit and you may have less of the insulin sensitivity with which to digest and regulate that blood glucose. So appetite effects, caffeine can temporarily suppress your appetite through the stress system activation, catecholamine release, and dopamine signaling. And this may reduce hunger temporarily, delay eating, and blunt perceived fatigue. So you feel more energized, and therefore, since your sympathetic nervous system is activated, you're not going to feel as inclined to eat. So undereating then further combined, it worsens this energy crash or the dysregulation or the anxious state that you're feeling. So, especially in already stressed individuals, again, just reiterating, eating something before, during, or relatively close after your morning coffee intake can help to mitigate this happening in your body. So, how does your morning coffee affect your recovery and your sleep? So the half-life of caffeine is roughly three to seven hours, and this is important. This means caffeine consumed later in the day may still significantly affect the brain at bedtime. People will say that they'll have their evening coffee and it won't affect them, and they'll fall asleep really quickly and they'll sleep great. And that may be true, but that caffeine is still in your system even when you're asleep, and so your body's trying to do something with it. So just because you fall asleep quickly doesn't mean that you're getting good sleep, doesn't mean that it's consistent sleep, and you likely have more awakening times. So caffeine can reduce total sleep time, sleep efficiency, and then also your deep sleep quality. Even when people fall asleep fine, it can still impair slow wave sleep, recovery quality, and nervous system restoration during your sleep time. And this is important because deep sleep is critical for memory consolidation, immune regulation, tissue repair, all of these systems. Sleep is one of the most important health factors for your body. It is when everything recovers and rests and repairs. And it's not just about the amount, it's about the quality of sleep that you're getting. That's really important. So recovery implications with caffeine and with poor sleep. Poor sleep combined with chronic caffeine reliance may contribute to that wired but tired physiology. Again, you're amping up that nervous system, you're amping up that um cortisol release. And so as a result, your body is on perpetually. Impaired recovery happens as a result of this, and therefore further nervous system dysregulation. People often use caffeine to compensate for inadequate recovery, which can then reinforce this cycle. You're not recovering appropriately, so you need more caffeine, you feel more fatigued afterwards because of the crash, and it just perpetuates itself. Caffeine can temporarily mask fatigue, but it does not get rid of it, and it doesn't replace recovery. So let's talk about some myths with coffee. Coffee cures hangovers and sobers you up. Caffeine may make you feel more alert, but it doesn't remove the alcohol from your body. Again, this goes back to the cortisol and the sympathetic nervous system stress response. It's helping you to wake up, it's kind of blunting that feeling of being fatigued from the alcohol, but ultimately the alcohol is in your system. So it might help to combat the feelings of it, but the alcohol is still in your body and still needs to be flushed out for you to actually be fully sober. Next myth: coffee is bad for the heart. Moderate coffee consumption of roughly two to five cups per day, again, keeping it under that daily limit of caffeine intake. It has been shown to have 11% roughly, is what the research is showing. Reduction in chronic heart disease risk and a lower risk of stroke, particularly in women. So, in addition to caffeine, coffee contains other compounds such as polyphenols, potassium, soluble fiber, and all of these things have been shown to reduce the risk of chronic heart disease. Next myth: dark roast coffee has more caffeine. Light roast coffees tend to actually have slightly more caffeine, apparently, as the roasting process breaks down the caffeine. So the darker roast would actually have less amounts of caffeine left because it had been roasted so much longer. I don't drink coffee. I just thought that one was interesting. And then the last myth I'll cover is coffee burns fat. Whilst coffee is not a fat burner, a cup of black coffee contains very few calories, which may help with weight management also due to appetite suppression. And I hesitate to say that because I don't want anybody to just go load up on plain black coffee and nothing else in the efforts to suppress their appetite and not eat and then lose weight. That is to say that while it will not directly burn fat, essentially the mechanism of action here is that you have the plain black coffee, there's very few calories in it, it does reduce your appetite, and as a result, you eat less, and then as a result of that, you're ideally losing weight because you're reducing your calories over time and essentially going into a deficit from there. So, my nursing adjustments for daily coffee caffeine intake. A lot of people are consuming more caffeine than they actually realize. The daily limit is 400 milligrams. That's roughly equivalent to four cups of brewed coffee, two energy drinks, but this varies heavily. Be sure to check the label, and then eight to ten cups of tea, depending on the type. So caffeine content varies dramatically depending on the roast, the brewing method, the size of the serving, and then the energy drink or the pre-workout formulation, depending on where you're taking this from. So, are different types better than others? Coffee, particularly black coffee, is the lowest calorie and least processed weight to consume coffee. So ultimately, I would say that that's the most health conscious. Because coffee, many coffee beverages contain so much sugar and syrups and heavy creamers and potentially other chemicals that you don't know about, those additions can significantly alter your caloric intake and therefore the metabolic effects, and then from their blood glucose response as well. However, black coffee is not necessarily the best for every individual. So some people will tolerate coffee best with a little bit of milk, with food, or just in smaller concentrations. We talked a little bit about some energy drinks. Ultimately, many of them contain very high caffeine doses, large sugar loads, and additional stimulants to help you get that more energized feeling. And so some combine caffeine, guarana, taurine, and other stimulatory compounds. So just pay attention to the label of the one that you're drinking and maybe double check where it's coming from to know specifically what you're getting, because again, some of them actually have higher amounts of caffeine in them than what they're actually reporting. And we want to make sure that we're staying underneath that 400 milligrams just for daily functioning and ultimately your health. So, why tolerance matters? We talked a little bit about this for the is caffeine addictive section, but people metabolize caffeine differently. Again, I'm super sensitive, but I know plenty of people that can have a lot more caffeine than I can and not really seem affected by it. Factors affecting caffeine metabolism include your body size, your stress, hormonal fluctuations, genetics, medications that you're on, liver function, but ultimately some people tolerate caffeine very well. Others experience anxiety, palpitations, GI upset, or insomnia, even with relatively low doses, even when it's taken early enough in the day. And this is another point that I want to make. The timing of caffeine is probably the most important part next to how much you're actually taking in. Caffeine later in the day can impair your sleep quality, the deep sleep, and then your nervous system recovery. So even if someone falls asleep quickly, caffeine can still reduce restorative sleep quality, particularly if it was taken later in the day, because again, that caffeine is still in your system and so it's still affecting your body. General recommendation avoid large caffeine later in the afternoon or evening. And this is because the half-life of caffeine is roughly three to seven hours. So that means that even up to seven hours after you consumed that beverage, you could still have at least half of it in your system. So take that into account based on how much you're taking in and what time, because that can really affect your recovery. And again, if you're not if you're not feeling recovered and you're feeling increased fatigue, you might be reaching for more caffeine, and that's going to perpetuate this cycle. So talking about caffeine on an empty stomach, I said this a few times. For some people, coffee without food may just worsen jitters, worsen reflux, maybe increase some anxious sensations. This is especially relevant in people with chronic stress, anxiety, GI sensitivity, poor sleep, or under eating tendencies. And food can help to buffer this. So ultimately, coffee feels very different and a regulated and supported body than versus a depleted one. So signs someone may need to reduce their intake. Possible signs of excessive caffeine intake can include anxiety. Anxiety, shakiness, GI upset, insomnia, irritability, afternoon crashes, dependence on caffeine for basic normal function, and then feeling wired but tired. That means that your body's dysregulated and it's not recovering appropriately. Caffeine should support function, not replace recovery. So, my key takeaways for you caffeine affects pretty much every system in the body. We talked about your mood and your GI tract and your brain and your recovery. The way caffeine is consumed and how much and what time can greatly change how it affects your physiology. Caffeine is not inherently bad. It's a stimulant interacting with your current physiology, stress levels, sleep, nutrition, and nervous system state. So essentially, it's going to just compound the state that your body is already in. If you know someone who loves their daily coffee, consider sharing this with them. Again, I'm not telling you that you can't have your daily coffee. I'm just giving you the information so that you can make the best decisions for your health and your body. If you found this helpful, you can subscribe for weekly conversations to learn more about your body and your health and how to help take care of it. You can reach out to me in the comments or email, or you can follow me on Instagram at Healthy Coded Podcast. I will respond to comments or DMs. If there's something you want to talk about, please let me know. Ultimately, thank you so much for listening. I love talking about this stuff, and I'll see you guys next week.