HSOS #51: The 90-Minute Coffee Rule: Fact or Fiction?

I keep seeing influencer after influencer talking about coffee and cortisol or some version of this, and a few of the claims bugged me, so I decided to actually look into the research myself and discuss on here. Here is the short version: your cortisol is supposed to rise in the morning, that part is completely normal, and while caffeine does add a little to that rise, your body adapts a lot more than people are giving it credit for. I also get into that popular rule about waiting 90 minutes before your first cup, and talk about why this whole conversation looks a little different once you are in perimenopause or menopause. By the end of the episode, you will have some real, research backed ways to think about your coffee habit without feeling like you need to panic over it. 

Let's talk.

Welcome to Her Season of Strength, where women over 40 reclaim their bodies, their energy, and their voices, without apologies. I'm Kim Duffy, registered dietitian, personal trainer, mom, and your biggest hype woman when it comes to aging like you mean it.

This show isn't about chasing skinny or counting wrinkles. It's about building real strength: physical, emotional, and hormonal. Each week, I'll share straight talking nutrition tips, sustainable fitness strategies, and conversations that help you feel powerful in your skin once again.

Menopause is not an ending, it is only the beginning. This is your season of strength.

What I Cover in This Episode:

• Why your cortisol is supposed to spike every single morning, and why that is actually a good thing, not a red flag
• The real research behind caffeine and cortisol, including the one nuance almost every influencer conveniently leaves out
• Whether the viral "wait 90 minutes before coffee" rule actually holds up once you look at the science behind it
• Why your daily coffee habit might not be spiking your cortisol the way you have been led to believe
• The exact caffeine dose researchers use in cortisol studies, and how it stacks up against your actual morning cup
• Why habitual coffee drinkers respond differently to stress than occasional drinkers, and why that matters
• How perimenopause and menopause quietly change the way your body handles both caffeine and stress
• The one simple pairing research shows can take the edge off caffeine jitters and blunt that cortisol spike
• Small, doable habits that support your stress response without asking you to give up your coffee
• Click here to get on the priority list for my brand new SUSTAIN 12 week program first, including early access, the lowest price of the round, and bonuses you will not find anywhere else

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Transcript

[00:00:00] Hi there, and welcome to Her Season of Strength, where women over 40 reclaim their bodies, their energy, and their voices without apologies. I'm Kim Duffy, registered dietitian, personal trainer, mom, and your biggest hype woman when it comes to aging like you mean it. This show isn't about chasing skinny or counting wrinkles.

[00:00:20] It's about building real strength, physical, emotional, and hormonal. Each week, I'll share straight-talking nutrition tips, sustainable fitness strategies, and conversations that help you feel powerful in your skin once again. Menopause isn't an ending. It's only the beginning. This is your Season of Strength. 

[00:00:40] Welcome back to Her Season of Strength. Before we dive into today's topic, I have to tell you about my week, 'cause it's exactly why we were talking about this today. So I was scrolling Instagram like I do most mornings, as I get up and I'm drinking my coffee and the irony is not lost on me, and in the span of about 10 minutes, I [00:01:00] watched four different wellness influencers talk and tell me that my morning coffee habit was wrecking my hormones.

[00:01:08] One said, "Don't touch caffeine for the first 90 minutes after waking or you're gonna spike your cortisol into the stratosphere." Then another said that, "Coffee on an empty stomach sends your adrenals into overdrive." And a third had a whole graphic with arrows and cortisol curve that honestly looked like it was drawn from memory rather than an actual research paper.

[00:01:29] And look, I get it. Cortisol is a hot topic right now, especially for, women over 40 who already feel like their bodies are doing something new and confusing every single week. But here's the thing, a lot of what's circulating around about coffee and cortisol, it's half true. It's taken out of context or it's flat out not backed up by research being cited or it just is coming from anecdotal evidence or someone's personal experience.

[00:01:57] So today I thought that [00:02:00] this would be a great opportunity to get to the bottom of it, not based on what sounds convincing in a 15-second video, but more about based on what actual research says. I wanna talk a little bit about what cortisol really is, and I know I've talked about this in previous episodes as well which is why, I wanna talk about why it's naturally highest in the morning, what caffeine actually does to it or how it affects it, and whether that whole 90-minute rule holds up under scrutiny.

[00:02:30] As well as why this might matter more for us after age 40 and what we can actually do if we wanna be a little bit more thoughtful about your morning cup without giving up something that we absolutely love, and I'm including myself in this for no good reason. So it's not a quit coffee episode, I promise.

[00:02:49] It's a more of a know what you're actually working with episode. So let's dive in. So starting out with just the basics because you can't understand what caffeine does to [00:03:00] cortisol until you really understand what cortisol is doing on its own. But cortisol is your body's primary stress hormone, and it's made by your adrenal glands.

[00:03:10] It's part of this system that we call HPA axis, and that stands for hypothalamic pituitary adrenal axis. I promise this is not gonna be some biology lesson, okay? But think of it as that communication between your brain and your adrenal glands, which are right around your kidneys. And it controls how much of that cortisol or that fight or flight hormone gets released and when.

[00:03:35] And here is what a lot of people don't realize, is that cortisol isn't just a stress hormone that shows up when something bad happens or if we're running away from, a tiger out in the wild or something like that. Excuse me, I don't know what happened to my voice just then. But it follows really a very predictable daily rhythm for most of us, whether we're stressed or not.

[00:03:55] It rises sharply in the first 30 to 45 minutes after we [00:04:00] wake up in the morning. Researchers actually have a name for this specific spike, and it's called cortisol awakening response, or CAR. And depending on the study, it can be anywhere from a 50 to 156% increase in our cortisol levels in our saliva compared to right before we woke up.

[00:04:23] So that's a huge jump, and it happens to every single one of us, every single morning, with or without coffee. After that peak rise, our cortisol declines steadily throughout the day. It hits its lowest point around midnight, and then in the second half of the night while we're sleeping, it starts climbing again to get you ready to wake up the next morning So why does this happen?

[00:04:52] This morning rise is in, in anticipation of waking up. Your body's basically giving you that built-in [00:05:00] energy boost before we even open our eyes. It mobilizes our blood sugar, it raises our blood pressure slightly, and it sharpens our alertness so that we're ready to meet the m- demands of the day.

[00:05:13] So now, a high cortisol level in the morning, it's not a sign that something's wrong with you. It's not your body being dysregulated. It is normal, it's protective, and it's an adaptive pattern that every healthy person has. So somebody talking about high cortisol levels is not, that, that doesn't mean something bad necessarily, right?

[00:05:39] But the problem comes in when research has shown a link between poor health outcomes and a flattened cortisol rhythm, and that just means that cortisol is not rising and falling the way it should. Maybe cortisol that stays high all day long, that's not [00:06:00] necessarily good, or cortisol spiking at the wrong times like maybe late at night or or we don't have that healthy morning rise like we should.

[00:06:13] And one more thing, because I promised you research and not hype, is that some newer studies have actually started questioning whether waking up itself is what triggers that cortisol spike or whether we're just catching the tail end of a rise that was already happening overnight. The science on kind of the exact mechanisms is still evolving, and I think it's important to say that out loud instead of pretending it's more settled than it is.

[00:06:42] When people get lab tests done and they're looking at cortisol in w- at one point in time, this is a side subject, but I did wanna mention this, that doesn't always tell us a lot. What is more helpful is when we do maybe salivary [00:07:00] cortisol tests and we are testing multiple times throughout the day to see what is actually happening.

[00:07:07] And even also multiple times at different periods of time, so maybe, one day or, then again next week or the following week or in six months or whatever. So let's talk a little bit about caffeine now, 'cause this is where things get interesting. So caffeine does stimulate additional cortisol release, okay?

[00:07:29] And it's been shown in many controlled studies, both when people are just sitting at rest and when they're under mental stress. One of the most detailed studies on this comes from a researcher named William Lovallo and his team, and they gave adults controlled doses of caffeine, somewhere in the two hundred and fifty to three hundred milligram range, and that's roughly two to three cups of coffee, and then they tracked their cortisol through saliva samples or spit samples across the day.

[00:07:58] Caffeine [00:08:00] reliably pushed cortisol higher than a placebo, meaning no caffeine. So if an influencer tells you caffeine raises cortisol, that part is actually true. But here's the nuance that almost never makes it into the fifteen-second version. People who drink caffeine every day build measurable tolerance to the effect, and even at a pretty moderate amount, around two hundred milligrams a day, which is about two cups of coffee.

[00:08:27] At higher habitual intakes or regular intakes, somewhere between three hundred and six hundred milligrams a day, the resting cortisol bump from a dose of caffeine can be almost completely blunted, right? Or it doesn't happen, or you don't see that extreme spike because their body has already adapted to it and they're not getting hit with that same fresh cortisol spike that someone who never drinks caffeine would get from that same few cups of coffee or whatever, soda or [00:09:00] wherever you're getting that caffeine.

[00:09:02] But here is the twist, and I think it's actually the most useful piece of information in this whole segment, and that tolerance mostly shows up when you are at rest. But when we add in some psychological stress, hab-habitual caffeine users have actually shown a bigger cortisol response to that stress compared to non-users.

[00:09:26] So it's not just the caffeine by itself that matters. It's that caffeine combined with stressful situations or maybe a stressful morning, and that combination may be doing more than either one of the two things alone. So if I had to sum up this in one sentence, it would be this: caffeine raising cortisol is true, but it is an incomplete picture without talking about dose, habitual use, and whether you're also dealing with real stress that morning.

[00:09:58] So now let's talk a little bit about [00:10:00] the elephant in the room, 'cause I know this is why a lot of you are still listening. The claim that you should wait 90 minutes after waking before you have your first cup of coffee so you don't stack caffeine on top of that natural cortisol peak. So this logic isn't crazy.

[00:10:17] The thought process is, don't pile a stimulant onto a system that's already elevated. Sounds, reasonable on the surface, but here is what kinda the direct research is actually showing us. Cortisol follows its own circadian pattern, rather r- circadian meaning when the light, it's light during the day, it's dark at night, right?

[00:10:38] And it, and our body naturally follows a rhythm or a pattern with sleep and awake cycles. So cortisol follows its own circadian pattern regardless of whether you drink your coffee. So there's no cons- to, controlled trial that has actually tested whether waiting exactly 90 minutes lowers your cortisol more [00:11:00] than waiting 20 minutes or drinking your coffee the second you wake up.

[00:11:04] Nobody's run that specific experiment and found that 90 minutes is just this magic number. And, this is the moment where I wanna challenge a popular claim instead of just repeating it because it sounds smart, right? A physiological plausible idea is not the same thing as a proven one Right?

[00:11:24] The 90-minute number specifically has never been tested head-to-head against other timing windows, like 20 minutes or 10 minutes or 60 minutes, in the research that's actually out there. So here's my honest kind of fair middle ground on this, is if you try delaying your first cup and you notice that you genuinely feel better, you're less jittery, you have steadier energy, that's completely valid reason to keep doing it.

[00:11:51] But do it because of what you're actually noticing in your own body, not because of a number you saw online told you, your hormones were at [00:12:00] risk if you didn't, especially coming from a questionable source, maybe somebody who's just going off of their own personal, I don't know, feelings, or what little bit they understand on the topic.

[00:12:14] So why specifically is this relevant for women who are listening to this podcast, us ladies in our midlife periods? As we move through peri and post-menopause, estrogen naturally declines. We talk about this all the time, right? And estrogen actually plays a regulatory role here that many people don't know about.

[00:12:35] Under normal circumstances, estrogen helps to strengthen our brain's negative feedback system, ess- essentially those breaks that keep that cortisol in check. Research on the menopause transition shows that, those breaks that we're talking about, they weaken in post-menopause. Some women will experience more reactivity [00:13:00] in their HPA axis, axis, and that just means bigger and maybe sometimes longer-lasting cortisol responses to those same stressors that used to hit us, and they didn't even bother us nearly as, as much.

[00:13:13] And believe me, I don't know about you, but things hit me different post-menopause. I tend to find, little things can set me off way more than I, I probably wouldn't have even cared before. And I always am like, "What's the deal?" So here's a translation. It's not that coffee suddenly becomes dangerous the day we turn 40 or 45, right?

[00:13:36] It's that our stress response system might be running a little hotter than it used to be, and I know you ladies know what I'm talking about. So when we stack that stimulant like caffeine on top of that system that's already more reactive we can generally feel different than it did when we were in our 20s and 30s.

[00:13:55] We can find that we have more jitters, more of that wired but [00:14:00] tired feeling. We can find that maybe we have more afternoon anxiety that seems to come out of nowhere. And this is exactly why looking at your own personal response, listening to your own body, that's gonna matter more now than following some generic rule that was probably tested on a 25-year-old subject, male probably, with a completely different hormonal picture than ours.

[00:14:28] So now let's talk a little bit about what you can do with this information. First of all, keep your intake moderate and consistent rather than sporadic and heavy, right? Remember that tolerance we talked about early, like steady, daily, moderate intake is exactly what builds it. Skipping caffeine for a few days and then loading up is much more likely to spar- to spike you than your regular two cups a day ever will.[00:15:00] 

[00:15:00] Second, consider pairing caffeine with L-theanine. What the heck is that? Let me tell you 'cause this actually has some solid research behind it. Multiple randomized placebo-controlled trials show that combining 100 to 200 milligrams of L-theanine with a moderate dose of caffeine, like maybe 50 to 100 milligrams, can reduce jitteriness and blunts that stress and that cortisol r- cortisol response while still giving us that little bit of benefit of caffeine.

[00:15:33] So this is why green tea and matcha can tend to help pick you up a little bit, but help you feel a little bit more calmer than a straight cup of coffee because those two things contain L-theanine. So I'm not saying you need to start supplementing with it or taking L-theanine supplements but those two things, the green tea and the matcha, can bo- both contain L-theanine.

[00:15:55] So maybe try changing rather than coffee we're drinking either of those things. [00:16:00] Next, eat something before or with your coffee. And I'll be honest with you, the direct research connecting this to cortisol specifically is it's a little thinner than I'd like, but eating first is gonna steady that blood sugar and reduce that reflux and that GI stress that some people can feel when they're consuming coffee on an empty stomach, and that lowers your overall stress load for the morning.

[00:16:25] And I'm a big proponent of this. I do believe that it's important when you are having coffee to try to have a little something to eat with it, rather than just on an empty stomach. Fourth, hydrating before your coffee. And this just kinda makes physiological sense since you wake up mildly dehydrated after a full night's sleep, and caffeine also has a little bit of a mild diuretic effect, meaning, meaning it makes you pee.

[00:16:50] And it can increase that dehydration effect. But, to be honest, it hasn't been directly shown to change your actual cortisol numbers. "Oh, I drank a giant [00:17:00] glass of water, and then I had my coffee." It's just a reasonable habit. Just, don't expect it to be some huge hormone hack, right?

[00:17:07] Fifth, if you're someone who generally feels wired or anxious or jittery after your morning coffee, kind of experiment with pushing your first cup back just a little later. Not because of that magic 90-minute rule, but because your own symptoms, like the jitters and the racing thoughts and the disrupted sleep that night, are a far better guide than a rule written for somebody else's body.

[00:17:33] And then lastly, support your overall stress system, so not just your coffee timing. Getting-- trying to get that morning sunlight, getting that movement and slow breathing. Those things can all help to regulate that HPA axis we've talking about this whole s- this wh- whole episode. So since caffeine seems to amplify that cortisol, specifically with stress, [00:18:00] lowering our baseline stress reactivity, it can matter just as much as when you drink your coffee and maybe even more So bringing this all around, let's summarize here.

[00:18:12] Your morning cortisol rise is normal. It's protective. It's not a problem that we need to fix. But caffeine can add to that rise, but your body genuinely adapts to it with regular moderate use. So that 90-minute rule you've probably seen, a dozen times this month sounds logical, but it's not backed by real direct evidence people claim it is.

[00:18:36] So don't let a number on the internet stress you out more than the coffee itself ever would. And after age 40, as women, our stress system we know that it's running a little hotter than it used to. So the most useful thing that we can do is to tune into how we personally feel rather than following that one-size-fits-all rule.

[00:18:57] We're all individuals. We're all-- we all have different [00:19:00] bodies, different hormones, different ways of handling things. So if you take one practical thing from today, let it be this: keep your intake steady and moderate. Consider trying pairing it with L-theanine, like green tea or matcha, if you're sensitive.

[00:19:16] Try to eat a little something and maybe drink a nice glass of water before your first cup of coffee, and then put real energy into those other levers like sunlight and movement and breath that can calm our whole stress system, not just our coffee cup. All right, so speaking of tuning into our body and building those good nutrition habits that actually last, we are in the runway for the Sustain program that's gonna be opening up in s- on September 28th, and the priority list for that next round is officially open right now.

[00:19:54] So being on that list is gonna get you three things. Can get you early access to register for [00:20:00] the program before it even opens up to the general public. It'll give you the lowest price that I will be offering for this entire round, locked in only for people on that priority list. And also, first access to the best bonuses I'm gonna offer and ones that will only be available to the people on the list.

[00:20:16] So if you've been waiting for a sign to finally get a little bit of support and help that's sustainable for the long term and rooted in real science, this is it. The link to join the priority list is in the show notes. And before you go, if this episode helped you to make sense of the whole coffee and cortisol conversation, take a screenshot and share it on Instagram or Facebook, and help other women who are in menopause to find the podcast.

[00:20:41] I greatly appreciate it. And also, if you just have a second and wanna leave a little review, let me know what you thought. I appreciate you so much. And as always, remember, this is about progress over perfection. We're in this for the long haul. This is your season of strength, and have a wonderful [00:21:00] day.