1 00:00:04,393 --> 00:00:08,056 Jen Oliver: Welcome to the, so that's Why podcast, where we unpack the 2 00:00:08,056 --> 00:00:10,246 science behind everyday questions. 3 00:00:10,306 --> 00:00:10,906 I'm Jen. 4 00:00:10,981 --> 00:00:11,401 Chris Smith: I'm Chris. 5 00:00:11,921 --> 00:00:12,436 Jamie Eynon: and, I'm Jamie. 6 00:00:13,726 --> 00:00:15,946 Jen Oliver: So tell me if this sounds familiar. 7 00:00:15,946 --> 00:00:19,966 You used to drink caffeine and feel like you could conquer the day, but 8 00:00:19,966 --> 00:00:24,256 now you drink it just to start feeling like you're running on a low battery. 9 00:00:24,526 --> 00:00:26,956 Why does caffeine lose its magic? 10 00:00:27,106 --> 00:00:29,626 Jamie Eynon: Yeah, and it's especially noticeable with coffee. 11 00:00:29,956 --> 00:00:31,726 There's a full on arms race going on. 12 00:00:31,936 --> 00:00:33,556 You start with a single shot latte. 13 00:00:34,036 --> 00:00:36,436 The next thing you know you're ordering a quadruple espresso 14 00:00:36,796 --> 00:00:39,256 and the barista is looking at you like you need an intervention. 15 00:00:40,306 --> 00:00:42,976 Chris Smith: Totally, and it probably won't surprise you that nearly 90% 16 00:00:42,976 --> 00:00:44,716 of adults consume caffeine daily. 17 00:00:45,496 --> 00:00:48,286 Um, it's the most widely used psychoactive substance on the planet, 18 00:00:48,736 --> 00:00:52,366 and yet most people have no idea why it gradually loses its punch. 19 00:00:52,846 --> 00:00:55,576 Jamie Eynon: And before we get into Jen, you are more of a tea person. 20 00:00:55,576 --> 00:00:55,906 Aren't you 21 00:00:56,146 --> 00:00:57,406 Jen Oliver: Guilty as charged? 22 00:00:57,406 --> 00:01:02,026 I'm a solid four cups of tea a day person, but I've noticed the same thing. 23 00:01:02,356 --> 00:01:06,226 You know, that first Brew of the morning used to give me like a proper lift, 24 00:01:06,226 --> 00:01:08,446 but now it just feels like maintenance. 25 00:01:09,376 --> 00:01:12,526 Chris Smith: That's because the mechanism is identical, whether it's coffee, 26 00:01:12,526 --> 00:01:16,126 tea, energy, drinks, or cola, the molecule, doing the work is the same. 27 00:01:16,276 --> 00:01:22,006 Caffeine tea has less per cup, typically, uh, 30 to 50 milligrams compared to about 28 00:01:22,006 --> 00:01:26,086 95 milligrams in coffee, but your brain responds to it in exactly the same way. 29 00:01:26,596 --> 00:01:29,986 So today we're talking about all caffeine, not just from coffee. 30 00:01:30,406 --> 00:01:33,736 Jamie Eynon: Plus we'll get into why some people can drink espresso at 9:00 31 00:01:33,736 --> 00:01:38,236 PM and sleep soundly while others are wide from a lunchtime cup, whether 32 00:01:38,236 --> 00:01:39,646 you can actually do anything about it. 33 00:01:40,696 --> 00:01:43,306 Jen Oliver: So what's really going on here, because most 34 00:01:43,306 --> 00:01:46,996 people think caffeine tolerance, it's just a minor inconvenience. 35 00:01:46,996 --> 00:01:48,886 Chris Smith: They do, but it is much more than that. 36 00:01:49,066 --> 00:01:53,416 In fact, a 2017 trial found that while caffeine still improved 37 00:01:53,416 --> 00:01:56,086 mental and physical performance after two weeks of daily use. 38 00:01:56,476 --> 00:02:00,436 Those benefits completely disappeared after one month of daily intake, 39 00:02:01,126 --> 00:02:02,956 Jamie Eynon: and that's a big deal though, isn't it? 40 00:02:03,136 --> 00:02:06,586 If you are relying on a cup of coffee or tea to get through a busy morning 41 00:02:06,856 --> 00:02:10,396 or power through a deadline, and it's basically doing nothing after a few weeks. 42 00:02:10,816 --> 00:02:12,166 You're just going through the motions. 43 00:02:12,676 --> 00:02:15,616 Jen Oliver: So the effects completely disappear after one month. 44 00:02:15,616 --> 00:02:21,316 So every January when I set my, you know, new, new year, new me goals, my caffeine's 45 00:02:21,316 --> 00:02:23,356 already checked out before I have, 46 00:02:23,656 --> 00:02:24,196 Chris Smith: I know, depression. 47 00:02:24,196 --> 00:02:24,346 Right? 48 00:02:25,726 --> 00:02:27,981 And here's where the part that like really gets people, because 49 00:02:28,381 --> 00:02:32,086 research shows that once that full tolerance develops habitual caffeine. 50 00:02:32,826 --> 00:02:35,826 Drinkers are essentially consuming it just to return to the baseline 51 00:02:35,946 --> 00:02:37,116 they had before they started. 52 00:02:37,626 --> 00:02:40,356 So without that morning cup, they'd actually feel worse than someone who'd 53 00:02:40,356 --> 00:02:41,556 never touched the caffeine at all. 54 00:02:42,366 --> 00:02:45,216 Jamie Eynon: So we're all locked in a cycle where our brew stops giving us 55 00:02:45,216 --> 00:02:48,876 a boost and just stops us feeling, or just stops us feeling terrible instead. 56 00:02:49,446 --> 00:02:52,266 Jen Oliver: I mean, it's a pretty sobering thought for something we all 57 00:02:52,266 --> 00:02:54,126 reach for first thing in the morning. 58 00:02:54,396 --> 00:02:57,906 But Chris, what is actually going on in our brains to cause this? 59 00:02:58,261 --> 00:03:01,561 Chris Smith: So to understand caffeine tolerance, we need to start 60 00:03:01,561 --> 00:03:03,391 with a molecule called adenosine. 61 00:03:03,721 --> 00:03:06,901 So throughout the day, your body produces this adenosine as a 62 00:03:06,901 --> 00:03:08,731 natural byproduct of burning energy. 63 00:03:09,091 --> 00:03:12,571 Adenosine binds to specific receptors in your brain, mainly called 64 00:03:12,571 --> 00:03:14,941 the A one and A two A receptors. 65 00:03:15,241 --> 00:03:19,291 And when it does, those receptors send you the signal you are tired, slow down. 66 00:03:19,921 --> 00:03:24,151 Jen Oliver: So adenosine is essentially your brain's built-in brake pedal, 67 00:03:24,391 --> 00:03:26,491 the longer you're awake and active. 68 00:03:26,816 --> 00:03:30,836 The more adenosine accumulates and the stronger that signal 69 00:03:30,836 --> 00:03:32,546 to be to rest becomes, 70 00:03:32,606 --> 00:03:33,056 Chris Smith: that's it. 71 00:03:33,326 --> 00:03:37,346 But what gets really interesting is that caffeine is structurally 72 00:03:37,376 --> 00:03:39,206 almost identical to adenosine. 73 00:03:39,536 --> 00:03:43,526 So when you drink coffee or tea, the caffeine molecules 74 00:03:43,526 --> 00:03:44,756 slot into those same receptors. 75 00:03:45,076 --> 00:03:46,276 But they don't activate them. 76 00:03:46,306 --> 00:03:48,826 They just sit there blocking, adenosine from getting through. 77 00:03:49,246 --> 00:03:51,706 Jamie Eynon: So the tired message is still being sent. 78 00:03:51,976 --> 00:03:54,136 Caffeine is just stopping it from being delivered. 79 00:03:54,616 --> 00:03:55,426 Chris Smith: Exactly right. 80 00:03:55,426 --> 00:03:58,396 So think of it as like noise canceling headphones for your 81 00:03:58,396 --> 00:03:59,746 brain's tiredness signals. 82 00:04:00,046 --> 00:04:01,906 The noise is still there, but you just can't hear them. 83 00:04:02,586 --> 00:04:05,406 Jen Oliver: Which is a really important distinction because that 84 00:04:05,406 --> 00:04:09,666 means caffeine doesn't actually create energy or alertness. 85 00:04:09,726 --> 00:04:12,396 It's just blocking your ability to feel tired. 86 00:04:12,726 --> 00:04:16,896 So the adenosine is still building up in the background the whole time. 87 00:04:17,106 --> 00:04:17,976 Chris Smith: Yeah, precisely. 88 00:04:17,976 --> 00:04:20,346 And this is really the key to everything. 89 00:04:20,346 --> 00:04:22,716 So your brain notices that it's tired signals. 90 00:04:23,251 --> 00:04:24,181 Aren't getting through. 91 00:04:24,181 --> 00:04:26,791 So it adapts by becoming more sensitive to them. 92 00:04:27,031 --> 00:04:30,391 In fact, it does this by growing more adenosine receptors to compensate. 93 00:04:30,811 --> 00:04:35,371 And a landmark study found that regular caffeine users increased adenosine 94 00:04:35,371 --> 00:04:38,611 receptors in the brain by about 20 to 30%. 95 00:04:39,031 --> 00:04:43,231 And another study showed that about 400 milligrams of caffeine per day, which 96 00:04:43,231 --> 00:04:47,971 is roughly four cups of coffee for just 14 days, was enough to significantly 97 00:04:47,971 --> 00:04:49,376 increase those receptors in humans. 98 00:04:49,966 --> 00:04:53,446 Jamie Eynon: So your brain is basically hiring extra staff to handle the 99 00:04:53,446 --> 00:04:55,516 complaints your coffee keeps ignoring. 100 00:04:55,996 --> 00:04:56,176 Chris Smith: Yeah. 101 00:04:56,176 --> 00:04:57,166 That's a great way of putting it. 102 00:04:57,346 --> 00:04:59,446 And once those extra receptors are in place. 103 00:04:59,971 --> 00:05:02,791 You now need more caffeine of course, to block a greater number of them. 104 00:05:03,241 --> 00:05:06,241 The dose that once made you feel sharp now barely gets you back to normal. 105 00:05:06,691 --> 00:05:08,551 Jen Oliver: And how quickly does this all happen? 106 00:05:08,551 --> 00:05:10,981 Because it feels like a gradual thing. 107 00:05:10,981 --> 00:05:15,241 But I can imagine the biology probably kicks in a lot faster than we'd expect 108 00:05:15,301 --> 00:05:15,901 Chris Smith: it is it? 109 00:05:15,901 --> 00:05:17,941 It's much faster once you read up it. 110 00:05:17,941 --> 00:05:19,006 It's quite surprising. 111 00:05:19,006 --> 00:05:22,111 In fact, one study found that complete tolerance to caffeine's 112 00:05:22,111 --> 00:05:25,891 effects on blood pressure and heart rate occurred after just one to 113 00:05:25,891 --> 00:05:27,931 four days of regular consumption. 114 00:05:28,451 --> 00:05:34,181 The alertness and, uh, focus benefits last a bit longer, but a 2024 review confirmed 115 00:05:34,181 --> 00:05:39,911 that measurable receptor changes occur within two weeks at moderate intake doses. 116 00:05:40,451 --> 00:05:44,351 Jen Oliver: So within a fortnight, your brain's already restructured itself 117 00:05:44,351 --> 00:05:46,241 to counteract your caffeine habit. 118 00:05:46,241 --> 00:05:48,191 I mean, that's incredibly fast. 119 00:05:48,341 --> 00:05:50,471 Jamie Eynon: And this explains the crash too, doesn't it? 120 00:05:50,986 --> 00:05:54,646 Because I've noticed if I skip my afternoon coffee, I feel worse than if 121 00:05:54,646 --> 00:05:56,086 I'd never had a coffee at all that day. 122 00:05:56,146 --> 00:05:56,266 Jen Oliver: Mm-hmm. 123 00:05:56,566 --> 00:05:57,796 Chris Smith: Yeah, that is spot on. 124 00:05:57,796 --> 00:06:00,196 And it's one of the most counterintuitive parts. 125 00:06:00,406 --> 00:06:02,986 'cause while caffeine, these occupying those receptors we talked 126 00:06:02,986 --> 00:06:05,446 about, adenosine keeps accumulating. 127 00:06:05,776 --> 00:06:08,686 So once the caffeine wears off and it's half-life is about. 128 00:06:08,936 --> 00:06:12,836 Four to six hours, all that built up adenosine floods in at once. 129 00:06:13,046 --> 00:06:16,526 So for chronic users, it's even worse because you've now got more 130 00:06:16,526 --> 00:06:17,876 receptors than you started with. 131 00:06:18,116 --> 00:06:21,146 So the tiredness signals hit harder than it would for a non caffeine drinker. 132 00:06:21,686 --> 00:06:26,156 Jen Oliver: So habitual caffeine drinkers actually experience more fatigue without 133 00:06:26,156 --> 00:06:28,256 it than someone who never drinks it. 134 00:06:28,586 --> 00:06:29,906 I mean, that's quite the trade off. 135 00:06:30,356 --> 00:06:30,716 Chris Smith: I know. 136 00:06:30,716 --> 00:06:31,466 Depressing isn't it? 137 00:06:32,036 --> 00:06:36,236 Um, a researcher described caffeine as a alone of the awake feeling rather 138 00:06:36,236 --> 00:06:38,186 than the creation of any new energy. 139 00:06:38,581 --> 00:06:41,251 So at some point you have to pay it back with interest. 140 00:06:41,551 --> 00:06:44,551 Jamie Eynon: Caffeine is basically a payday loan for your brain. 141 00:06:44,791 --> 00:06:45,721 Good short term. 142 00:06:45,721 --> 00:06:47,551 But the repayment plan is rough. 143 00:06:48,091 --> 00:06:51,811 Jen Oliver: And the twist is that not everyone gets the same repayment plan. 144 00:06:52,021 --> 00:06:56,011 Genetics play a big role in how caffeine affects different people. 145 00:06:56,161 --> 00:06:56,731 Chris Smith: That's right. 146 00:06:56,731 --> 00:07:01,531 And twin studies suggest it that genetics account for about 36 to, 147 00:07:01,531 --> 00:07:05,611 I think 58% of the differences in how people respond to caffeine. 148 00:07:06,256 --> 00:07:07,906 And there are two key genes involved here. 149 00:07:08,356 --> 00:07:13,186 The first one is called the CYP one A two, which produces the enzyme 150 00:07:13,186 --> 00:07:17,836 responsible for metabolizing about 95% of the caffeine in your body. 151 00:07:18,316 --> 00:07:21,376 And a small variation in this gene can determine whether you 152 00:07:21,376 --> 00:07:23,416 are a fast or a slow metabolizer. 153 00:07:23,956 --> 00:07:28,516 So fast metabolizers down caffeine about one and a half or 1.6 times 154 00:07:28,696 --> 00:07:30,496 faster than a slow metabolizer. 155 00:07:30,946 --> 00:07:33,796 Jamie Eynon: So that friend who swears they can have an espresso 156 00:07:33,796 --> 00:07:35,146 after dinner and sleep fine. 157 00:07:35,536 --> 00:07:36,376 They're not making it up. 158 00:07:36,466 --> 00:07:37,636 Chris Smith: No, not at all. 159 00:07:37,636 --> 00:07:42,706 And about 10% of the population carry a genetic variant, um, linked to 160 00:07:42,706 --> 00:07:46,696 higher caffeine tolerance, and that allows them to consume larger amounts 161 00:07:46,696 --> 00:07:48,586 later in the day without side effects. 162 00:07:49,456 --> 00:07:54,376 The second gene called adora two A affects the adenosine receptor itself. 163 00:07:54,736 --> 00:07:57,856 Different variations determine whether caffeine is more likely to keep you 164 00:07:57,856 --> 00:07:59,896 awake or more likely to make you anxious. 165 00:08:00,931 --> 00:08:04,621 Jen Oliver: So your entire relationship with caffeine, how much it wakes you 166 00:08:04,621 --> 00:08:09,241 up, how quickly you build tolerance, whether it keeps you up at night, 167 00:08:09,481 --> 00:08:11,461 is heavily influenced by your DNA. 168 00:08:11,821 --> 00:08:14,641 So that explains why some people can drink caffeine late in the 169 00:08:14,641 --> 00:08:19,021 day and feel fine while others are wired for hours after just one 170 00:08:19,021 --> 00:08:20,641 cup in the afternoon, which is me. 171 00:08:20,791 --> 00:08:21,331 That is me. 172 00:08:21,421 --> 00:08:24,751 Jamie Eynon: This explains every argument in every office, kitchen, ever. 173 00:08:25,096 --> 00:08:27,166 How can you drink at 4:00 PM How can you not? 174 00:08:27,616 --> 00:08:30,856 Turns out we're all just having a genetics debate and we didn't know it. 175 00:08:31,576 --> 00:08:31,966 Chris Smith: Totally. 176 00:08:31,966 --> 00:08:33,796 And there's a myth worth addressing here. 177 00:08:33,796 --> 00:08:34,451 I'm always the myth buster. 178 00:08:34,461 --> 00:08:35,641 Jen Oliver: You are the Myth Buster 179 00:08:35,661 --> 00:08:36,556 or Captain Sensible. 180 00:08:36,616 --> 00:08:40,576 Chris Smith: I know so many people believe they've successfully adapted 181 00:08:40,636 --> 00:08:44,761 to less sleep by using caffeine, but multiple studies show that while 182 00:08:44,806 --> 00:08:46,426 you might feel less acutely tired. 183 00:08:46,801 --> 00:08:50,371 The cognitive performance continually deteriorates. 184 00:08:50,431 --> 00:08:52,951 So your brain is actually becoming numb to its own impairment. 185 00:08:53,431 --> 00:08:56,371 Jen Oliver: So we touched on this in our sleep episode, the idea that 186 00:08:56,371 --> 00:09:00,121 people can accumulate sleep debt without realizing how impaired they 187 00:09:00,121 --> 00:09:05,101 are, and then caffeine masks that even further, which is why it's such a trap. 188 00:09:05,341 --> 00:09:06,751 Jamie Eynon: Uh, what about age? 189 00:09:06,841 --> 00:09:10,051 I definitely feel like coffee hits differently now compared 190 00:09:10,051 --> 00:09:11,131 to how it did in my twenties. 191 00:09:11,281 --> 00:09:11,971 Chris Smith: No, absolutely. 192 00:09:11,971 --> 00:09:14,881 So caffeine, metabolism slows with age, meaning it stays 193 00:09:14,881 --> 00:09:15,476 in your system for longer. 194 00:09:16,111 --> 00:09:18,871 This is why many people find they can't tolerate a late afternoon 195 00:09:18,871 --> 00:09:20,311 coffee as they get older. 196 00:09:20,461 --> 00:09:24,031 They're not just imagining it, so their liver is simply processing it more slowly, 197 00:09:24,721 --> 00:09:28,291 Jen Oliver: which explains why some people naturally switch to lower 198 00:09:28,291 --> 00:09:32,701 caffeine like decaf tea over time, because lower caffeine per cup means 199 00:09:32,701 --> 00:09:36,976 less impact on your sleep, especially if your metabolism slows with age. 200 00:09:37,086 --> 00:09:41,521 Jamie Eynon: Alright, so the big question we actually, can we 201 00:09:41,521 --> 00:09:42,721 actually do anything about this? 202 00:09:42,721 --> 00:09:44,221 Or are we stuck in an endless cycle? 203 00:09:44,611 --> 00:09:46,201 Chris Smith: Yeah, you can absolutely manage it. 204 00:09:46,231 --> 00:09:50,011 And the most effective approach is strategic use of caffeine rather 205 00:09:50,011 --> 00:09:51,421 than habitual use of caffeine. 206 00:09:51,691 --> 00:09:55,531 So research shows that using caffeine on only days when you genuinely need 207 00:09:55,531 --> 00:09:59,761 peak performance, let's say two to three days a week, prevents that steady 208 00:09:59,761 --> 00:10:01,741 receptor buildup that causes tolerance. 209 00:10:02,971 --> 00:10:06,781 Jen Oliver: And for people who wanna reset their tolerance, studies show that. 210 00:10:07,291 --> 00:10:08,941 Brain receptor sensitivity. 211 00:10:09,001 --> 00:10:12,901 It typically normalizes within about two weeks of stopping caffeine. 212 00:10:13,261 --> 00:10:17,761 After a two week break, your sensitivity returns roughly to 70, 80% of its 213 00:10:17,761 --> 00:10:21,871 original level, but heavy users obviously might need, you know, up 214 00:10:21,871 --> 00:10:23,671 to two full months for a full reset, 215 00:10:24,451 --> 00:10:25,681 Jamie Eynon: two weeks without coffee. 216 00:10:25,771 --> 00:10:27,176 I think most people would rather live. 217 00:10:27,781 --> 00:10:30,451 With weaker caffeine effects than deal with two weeks with no coffee. 218 00:10:30,481 --> 00:10:31,021 Jen Oliver: Definitely. 219 00:10:31,231 --> 00:10:32,551 Chris Smith: Uh, yeah, I think that's fair. 220 00:10:32,551 --> 00:10:34,711 And there is a gentler option you can take. 221 00:10:34,711 --> 00:10:39,871 So gradually reducing that caffeine intake by about 25% every 10 days, 222 00:10:40,021 --> 00:10:42,691 that will produce significantly fewer withdrawal symptoms. 223 00:10:42,991 --> 00:10:47,101 And research shows that about 80% fewer severe effects compared 224 00:10:47,101 --> 00:10:48,331 to stopping abruptly for people. 225 00:10:48,991 --> 00:10:51,811 Jen Oliver: It is also worth mentioning that caffeine withdrawal 226 00:10:51,811 --> 00:10:53,941 is actually clinically recognized. 227 00:10:53,941 --> 00:10:54,901 It's no joke is it? 228 00:10:54,901 --> 00:10:59,071 You know, people experience symptoms such as headaches, fatigue, 229 00:10:59,131 --> 00:11:04,621 irritability, difficulty concentrating, and those symptoms typically peak 230 00:11:04,681 --> 00:11:07,951 a few days after, but then they do resolve within a couple of weeks. 231 00:11:09,121 --> 00:11:10,801 Jamie Eynon: And that applies to tea drinkers too? 232 00:11:11,401 --> 00:11:13,741 Chris Smith: It does, although tea drinkers often have a smoother 233 00:11:13,741 --> 00:11:16,831 experience 'cause their daily caffeine intake tends to be lower. 234 00:11:17,071 --> 00:11:21,841 If like Jen, you're on about four cups of tea a day, you're looking at maybe 150 235 00:11:21,841 --> 00:11:23,821 to 200 milligrams of caffeine in total. 236 00:11:24,241 --> 00:11:27,601 If you compare that to the same number of coffees like four a day, 237 00:11:27,601 --> 00:11:29,161 that's closer to 400 milligrams. 238 00:11:29,491 --> 00:11:32,671 So the withdrawal is proportionate to the intake. 239 00:11:32,821 --> 00:11:34,231 Jen Oliver: I mean, that's reassuring. 240 00:11:34,531 --> 00:11:38,431 So tea drinkers like myself might build tolerance more slowly. 241 00:11:38,821 --> 00:11:40,231 And have a gentler time. 242 00:11:40,231 --> 00:11:40,861 Resetting 243 00:11:41,401 --> 00:11:45,751 Chris Smith: generally yes, and keeping daily intake below roughly 200 244 00:11:45,751 --> 00:11:50,371 milligrams, which is about two standard coffees or forties that slows the 245 00:11:50,371 --> 00:11:51,991 rate at which that tolerance builds. 246 00:11:52,351 --> 00:11:56,731 And one study found that 400 milligrams of caffeine daily for only seven 247 00:11:56,731 --> 00:12:01,051 days, had no measurable receptor effect, but the same dose for 14 days. 248 00:12:01,051 --> 00:12:01,291 Did. 249 00:12:01,786 --> 00:12:05,416 So moderate tea drinking may sit in that sweet spot where you're getting 250 00:12:05,416 --> 00:12:08,266 some benefit without triggering those major receptor changes. 251 00:12:08,926 --> 00:12:11,236 Jamie Eynon: So it's about finding that balance where you are getting the 252 00:12:11,236 --> 00:12:15,706 benefit without tipping into the zone where your brain starts remodeling. 253 00:12:16,335 --> 00:12:18,375 Jen Oliver: And here's something else that's really interesting. 254 00:12:18,375 --> 00:12:22,485 For anyone who exercises, caffeine still appears to boost physical 255 00:12:22,485 --> 00:12:25,365 performance, even intolerant individuals. 256 00:12:25,665 --> 00:12:29,955 And a study showed that caffeine supplements, they enhance physical 257 00:12:29,955 --> 00:12:32,715 performance by an average of around 11%. 258 00:12:33,045 --> 00:12:36,495 So those that are habitual uses, they might need a higher dose, but the 259 00:12:36,495 --> 00:12:40,695 benefit doesn't disappear entirely the way the mental alertness benefit does. 260 00:12:41,175 --> 00:12:41,475 Chris Smith: No. 261 00:12:41,475 --> 00:12:42,765 And 11% is huge, isn't it? 262 00:12:42,825 --> 00:12:42,915 Jen Oliver: Mm-hmm. 263 00:12:43,305 --> 00:12:45,435 Chris Smith: But the catch is that caffeine improves performance. 264 00:12:45,750 --> 00:12:46,950 But can disrupt sleep. 265 00:12:47,190 --> 00:12:49,560 And of course poor sleep undermines recovery. 266 00:12:49,860 --> 00:12:52,860 So for anyone exercising regularly, the timing matters. 267 00:12:53,160 --> 00:12:56,490 Ideally, no caffeine within about eight hours of bedtime. 268 00:12:57,030 --> 00:12:58,110 Jamie Eynon: That's really interesting because. 269 00:12:59,160 --> 00:13:00,600 It creates a real tension. 270 00:13:00,900 --> 00:13:03,930 You want the performance boost, but not at the cost of your sleep. 271 00:13:04,380 --> 00:13:06,510 Jen Oliver: And I think, uh, you know, most of us have probably been 272 00:13:06,510 --> 00:13:10,260 in that cycle where we drink the caffeine to compensate for poor sleep. 273 00:13:10,590 --> 00:13:14,460 Then the caffeine disrupts our sleep, so then we need more the next day. 274 00:13:14,670 --> 00:13:17,220 It's, it is the definition of a vicious circle. 275 00:13:17,370 --> 00:13:18,330 Chris Smith: Yeah, it really is. 276 00:13:18,330 --> 00:13:21,510 And, and it connects directly to what we discussed in previous episodes. 277 00:13:21,510 --> 00:13:23,130 So sleep quality affects everything. 278 00:13:23,250 --> 00:13:23,760 Mood. 279 00:13:24,225 --> 00:13:29,865 Cognitive function, uh, exercise recovery, even how your body manages inflammation 280 00:13:30,315 --> 00:13:33,135 and caffeine tolerance sits right in the middle of all these systems. 281 00:13:33,345 --> 00:13:34,815 Jamie Eynon: Uh, and hydration too, right? 282 00:13:35,055 --> 00:13:39,045 If you're drinking four or five cups of coffee a day or tea because one 283 00:13:39,045 --> 00:13:41,715 doesn't cut it anymore, that's a lot of fluid moving through your system. 284 00:13:41,835 --> 00:13:42,915 Jen Oliver: Yeah, that's a good point. 285 00:13:43,395 --> 00:13:46,935 At normal consumption levels, coffee and tea are both hydrating and we 286 00:13:46,935 --> 00:13:48,945 covered that in our hydration episodes. 287 00:13:49,320 --> 00:13:53,880 But when tolerance pushes intake higher, it's worth being aware 288 00:13:53,880 --> 00:13:55,530 of your overall fluid balance. 289 00:13:55,690 --> 00:13:56,380 Chris Smith: Yeah, totally. 290 00:13:56,380 --> 00:13:58,780 And what is really striking is that caffeine tolerance is a 291 00:13:58,780 --> 00:14:02,440 perfect example of how our bodies constantly adapt to maintain balance. 292 00:14:02,530 --> 00:14:07,210 And we saw the same principle with sweat acclimatization, with sleep cycles, 293 00:14:07,240 --> 00:14:11,170 even with cholesterol regulation, the body's always adjusting and adapting. 294 00:14:13,270 --> 00:14:16,120 Jamie Eynon: So understanding this isn't just about coffee, it's about 295 00:14:16,120 --> 00:14:18,160 us understanding how your body works. 296 00:14:18,190 --> 00:14:18,700 Full stop. 297 00:14:19,990 --> 00:14:23,710 Jen Oliver: So why does your morning coffee or tea stop working? 298 00:14:24,280 --> 00:14:27,340 Chris Smith: It stops working because your brain physically adapts to 299 00:14:27,340 --> 00:14:31,780 caffeine by growing more adenosine receptors, sometimes 20 to 30% more. 300 00:14:32,260 --> 00:14:36,250 The dose that once blocked enough receptors to make you feel alert now 301 00:14:36,250 --> 00:14:38,020 can't keep up with increased numbers. 302 00:14:38,380 --> 00:14:41,710 You end up drinking caffeine just to feel the way you would naturally without it. 303 00:14:42,340 --> 00:14:45,760 Jamie Eynon: So we went from one cup making us feel super human to four 304 00:14:45,760 --> 00:14:47,530 cups making us feel merely human. 305 00:14:48,130 --> 00:14:50,950 And we've been calling that a coffee habit when it's actually 306 00:14:50,950 --> 00:14:52,570 a brain renovation project. 307 00:14:53,335 --> 00:14:57,325 Jen Oliver: So that's why caffeine stops working, and now you know that your 308 00:14:57,325 --> 00:15:02,605 relationship with it is shaped by your genetics, your habits, and your brain's 309 00:15:02,605 --> 00:15:05,155 relentless drive to maintain balance. 310 00:15:05,425 --> 00:15:08,755 But the good news is once you understand the mechanisms, you can 311 00:15:08,755 --> 00:15:10,975 work with it rather than against it. 312 00:15:11,395 --> 00:15:11,660 Chris Smith: You can. 313 00:15:11,845 --> 00:15:15,205 And the advice is to use caffeine strategically, not habitually. 314 00:15:15,445 --> 00:15:20,305 So a periodic reset or simply cutting back can restore much of that original effect. 315 00:15:20,605 --> 00:15:22,255 Sometimes less really is more. 316 00:15:22,760 --> 00:15:24,260 Jen Oliver: So that's it for this week. 317 00:15:24,320 --> 00:15:26,570 Make sure you hit that subscribe button. 318 00:15:26,810 --> 00:15:30,560 We're unpacking the science behind everyday questions each week, 319 00:15:30,980 --> 00:15:34,550 and tell us in the comments what questions you'd like us to explore. 320 00:15:34,970 --> 00:15:38,480 Thanks for geeking out with us, but for now, that's it from me. 321 00:15:38,840 --> 00:15:39,355 Jamie Eynon: That's it from me. 322 00:15:39,980 --> 00:15:40,670 Chris Smith: And that's it from me. 323 00:15:41,030 --> 00:15:41,750 Jen Oliver: Bye for now.