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Why Do We Get Afternoon Energy Crashes? · So That's Why

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Jen: Welcome to the So That's Why podcast, where we unpack the
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science behind everyday questions.
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I'm Jen.
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chris: I'm Chris.
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Matt: And I'm Matt.
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Jen: Right.
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2:36, it doesn't sound like a special time, does it?
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But according to a survey of 2,000 UK adults, that's the exact
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moment most people hit the wall.
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Matt: 2:36?
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Jen: Yep, 2:36.
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Your eyelids get heavy, emails slow down, and suddenly the biscuit tin
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starts calling your name in a way that it definitely wasn't doing at 11:00 AM.
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So why do we get afternoon energy crashes, and why are they so consistently on time?
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Matt: I'm still amazed by the 2:36.
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I mean, that's, that's very specific, isn't it?
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Not kind of mid-afternoon, after lunch.
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It's just 2:36.
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Someone clearly looked at the data and went, "Yep, that's the moment society
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seems to, well, collectively just give up- … for the rest of the day."
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chris: It is, and it is quite specific, isn't it?
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And actually, it's not just one data set.
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So there was a separate US survey that found the average
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low point there is 2:06 PM.
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So still pretty close, right?
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So different people, different country, but the same kind of window.
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. Matt: But the Brits are 30 minutes in front maybe.
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chris: Just the way it should be.
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Efficiency.
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Jen: We love our American viewers.
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Matt: Yeah, and I… Well, yes, absolutely.
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I mean, I love this, and I love there's this sort of glo-
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semi-global agreement, isn't there?
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Sort of around 2 o'clock, 2:30, every office just sort
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of quietly shifts, doesn't it?
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And, um, tea gets made.
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Someone goes for a quick walk.
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I shouldn't say this, but I have a little thing in the back of my van.
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I can go for a quick nap.
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Uh, but meetings, they sort of mysteriously get pushed to tomorrow.
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Uh, I do feel it actually.
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Jen: Yeah, totally.
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But here's the interesting bit.
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Most people assume that it's just a lunch thing, but it isn't.
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It happens whether you eat or not.
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chris: That's it, and that is the surprise.
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So lunch does contribute, but it's not the main driver.
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So what we're actually seeing here is four biological systems all peaking at
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the same time and reinforcing each other.
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Jen: And that's the thing really.
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Each one on its own is manageable, but it's the stacking of them
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that does the real damage.
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Matt: So the crash isn't one thing breaking.
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It's four things showing up at exactly the same time when you don't want it to.
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Jen: Exactly.
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Matt: Exactly.
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Everyone's going, "What's he talking about?"
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Jen: It is.
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People need to Google Accrington Stanley, don't they?
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And they will find out what's going on.
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Anyway, so before we get into what causes it, it's worth
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us understanding the impact.
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A Slack survey of over 10,000 desk workers found only one in four people
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felt productive between 3:00 and 6:00 PM.
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And in a UK survey, 12% said they'd actually fallen asleep in a
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meeting- … and 10% made noticeable work errors during that window.
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Matt: 12% asleep in meetings.
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I've definitely been one of them.
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it kinda feels low, I guess.
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I thought the number would've been higher.
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You know, the lower, higher thing, I would've definitely gone higher than 12%.
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Jen: Yeah.
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Me too.
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Matt: Maybe the rest of us are just in denial.
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I don't know.
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Jen: Absolutely.
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Totally.
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chris: Yeah.
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There's probably a few people fibbing there, isn't there?
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Jen: Yeah.
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chris: But it shows up in performance data too.
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So there was a report by the, American Academy of Sleep Medicine, and they
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concluded that cognitive performance drops by about 15 to 25% in the afternoon.
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So that includes reaction time, attention, decision-making, all of it.
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So basically, that tells me if you're gonna be having major surgery,
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get them to do it in the morning-
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not the afternoon.
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Yeah, definitely.
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And there was a study of around 800 office workers over two
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years, and that backs this up.
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They saw real dips in accuracy, so there was more typing errors and reduced
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computer activity in the afternoon.
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So it's not just self-reported, there's real evidence.
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Matt: Which probably explains a few of my afternoon emails.
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I've actually had to start… I don't know if you've done this, start rereading
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everything I send out around 4:00 just in the order of self-preservation-
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Jen: Yeah
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Matt: more than anything.
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chris: Yeah, me too.
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Yeah.
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Or just put it off till tomorrow.
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Start again.
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Jen: Yeah.
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Yeah, definitely.
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chris: Um, but that 15 to 25% drop, it matters, doesn't it?
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Because if you think, you know, if you're driving or you're managing people,
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making decisions under pressure, or doing that surgery I mentioned- Mm-hmm
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you know, it's not just I'm feeling a bit tired.
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This is like a measurable change.
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Jen: Okay, so what's actually going on at 2:36 PM then?
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chris: So these, these four biological processes I mentioned,
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these forces, they all show up around the same time, and they don't just
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cancel each other out, they stack up.
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Jen: And we've touched on parts of this before, haven't we?
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Like the post-lunch fatigue, caffeine, sleep pressure.
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But today we're looking at how all of these overlap.
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chris: Yep.
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And the first force is your circadian rhythm.
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And here's one for the fact fans actually out there.
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So most people don't realize this, but your body doesn't just dip once a day.
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It actually dips twice.
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Matt: Twice?
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I know of one that I never really get up again from, but twice?
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chris: I know.
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So there's a dip in the early hours of the morning when you're asleep, which is
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obviously pretty handy to have a dip then.
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Oh, that's why I didn't
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Matt: know about it then, yeah.
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chris: Yeah.
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But, but yeah, the other dip is in the middle of the afternoon
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that we're talking about, which is obviously a little bit less handy.
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Jen: And during that afternoon dip, your core body temperature, it drops slightly,
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only just half a degree to a degree, which is closely linked with reduced
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alertness and a slower reaction time.
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Matt: So my, I just need five minutes feeling then at 2:00 is basically my
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internal thermostat agreeing with me.
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chris: Pretty much, yep.
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And there's also evidence that the brain's motivation… no, motivation circuits,
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sorry, are less active at that time.
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So it's not just tiredness, it's reduced drive as well.
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Jen: And that study, that's, that was from a study at Swinburne University.
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So they mapped out the brain's reward center across the day, and they
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found it was genuinely quieter in the afternoon, which explains why
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everything suddenly feels more effortful.
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Matt: Yeah.
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And so it's, it's not that I've gotten worse at my job,
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thank the Lord, at 2:00 PM.
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My brain's motivation department has just sort of gone slightly
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on a long tea break maybe.
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Jen: It's good that you're not getting worse at your job.
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Matt: You should tell Michelle.
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Well, you know.
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Jen: Okay.
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So the second force in sleep is sleep pressure.
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So while you're awake, there's a chemical called adenosine, and that
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builds up in your brain, and it's your natural signal to slow down.
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So the longer you've been up, the stronger it gets.
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chris: Yeah, that's it.
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And by mid-afternoon, so roughly six to 10 hours after you've woken up,
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it's high enough, this change is high enough to noticeably affect alertness.
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And adenosine, by the way, it's the same molecule that caffeine blocks.
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So, we went through this in the coffee episode in a bit more detail,
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but it explains why also a strong coffee alone in the afternoon
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doesn't always do the trick.
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Jen: So that's when that rise in sleep pressure meets the circadian dip.
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They don't just add together, they amplify each other.
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Matt: So it's not, it's not one thing just knocking you down.
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It's a couple of systems basically teaming up together at the same time.
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Tag teaming, maybe.
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chris: Exactly.
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Or exactly?
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Matt: Exactly.
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chris: I can't, I can't do it.
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Jen: People really need to
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Google-
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chris: Yeah.
7:35
I'm so sorry
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Jen: Accrington
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Stanley
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again.
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chris: I'm so sorry.
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Was it Ian Rush?
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Was, was he-
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Matt: Yeah, yeah
7:39
… chris: linked to it as well?
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Matt: Yeah, yeah.
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chris: Yeah.
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Matt: He, he said, "If I-"
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chris: It's milk.
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Matt: Yeah, yeah.
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"If I don't drink-" "If I don't drink my milk one day- Yeah … I
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can play for Accrington Stanley."
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chris: Accrington
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Jen: Stanley.
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chris: Stanley.
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Who are they?
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Sorry, I'm so, I'm so sorry.
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Matt: Exactly.
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Everyone's just
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really confused.
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chris: I've got no idea what we're talking about now and we
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were talking about cortisol.
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Jen: Third
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force.
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Yeah.
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Third force.
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chris: Yes.
8:00
So the third force is… What was the second force?
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The third force is cortisol.
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So, you'll know cortisol as being the stress hormone and when you hear
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stress hormone, you assume it's bad.
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But cortisol is one of your main alertness hormones too.
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Jen: Yeah, so cortisol surges within, like, 30 to 45 minutes of you waking,
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and its official name is called the cortisol awakening response, and that
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then steadily declines across the day.
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So by mid-afternoon it can be 50 to 70% lower than morning
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levels in healthy adults.
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Matt: So we're basically running on a falling level of alertness hormone
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before lunch is even finished.
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chris: Yep, that's right.
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And of course, you've got another factor here, which is stress.
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And stress complicates it further because when it comes to
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chronic stress, it flattens that cortic- cortisol response curve.
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So when you're stressed, you don't always get that strong cortisol
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morning boost, and it doesn't recover properly during the afternoon either.
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Jen: Which means people who are r- already stressed, they often feel
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the afternoon crash more, not less.
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And then you also get that wired but tired pattern where you're flat in the
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afternoon, and oddly, and annoyingly-
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awake at night.
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Matt: I just like that wired but tired phrase.
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And of course this makes complete sense, doesn't it, of the 11:00
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PM second wind that turns up just as you're trying to get to sleep.
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Yeah.
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And it really does affect my wife, if she's watching.
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It's incredible.
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chris: I know.
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It's so annoying.
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You're kind of wide awake at 11:00 o'clock but you couldn't
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do that email at 4:00 o'clock.
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Matt: Yeah, yeah.
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Yeah.
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Jen: Yeah.
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chris: And then we've got the fourth force, which is food.
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So we cover this in a lot of detail in another episode, but the key
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point when it comes to food is simple, that lunch doesn't cause
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the crash, but it can amplify it.
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Jen: And did you know, helpful, but a high refined carb lunch without protein,
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that tends to make the dip sharper.
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So it's no surprise at all that a balanced meal smooths it out, although
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it doesn't actually remove it.
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Matt: So food then isn't the villain, is what we're saying.
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It just decides whether the slope is gentle or steep,
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which is an analogy I like.
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Okay, so if all four are happening to everyone, why does it feel so much
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worse for some people than for others?
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chris: Yeah, so it's because there are amplifiers on top of those
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four forces that I mentioned.
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So there are… Well, there'll be no surprise with this, and
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I'm sorry to be Mr. Repetitive-
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Jen: Feel
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like that's a new name.
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chris: Yeah.
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Or Captain Repetitive.
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Matt: We need to keep a track of the actual name.
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Jen: Captain
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Sensible.
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Matt: Captain Sen-
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Jen: Myth Buster.
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Yeah.
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Mr. Repetitive.
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chris: I've been called far worse over the years, so.
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But yeah, to be a bit repetitive on this, the biggest is sleep deprivation.
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It affects it so much.
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Jen: Yeah, and in surveys, around 45% of people say poor sleep is the main reason
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their afternoon crash is harder, because it lowers your baseline alertness, so
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the dip hits from a worse starting point.
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Matt: So you're not just dipping, you're dipping from a lower point already.
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chris: That's it.
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And then there's a second amplifier, which is dehydration, and even mild dehydration,
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so 1 or 2% of body water loss, that can affect attention and fatigue.
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Jen: And that's been backed up by the research as well.
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So there was a meta-analysis of 33 studies, and that shows that at that
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level you can see clear drops in attention, memory, and coordination.
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You know, but what's interesting is the brain actually has to work harder
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to keep performance up, which is part of why it feels mentally draining.
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Matt: So by lunchtime, if you're… or if you've barely had any water, guilty as
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charged, you're already setting yourself up for that 2:00 PM drop, aren't you?
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chris: You are.
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And I'm sorry to come after tea and coffee drinkers, but- … it's
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another amplifier here to think about, and it's often overlooked,
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but it's actually caffeine timing.
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So caffeine has a half-life of around five to seven hours.
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So that means that in that time, in that five to seven hours, the
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body has eliminated half of it, but half still remains in your system.
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Jen: So a 3:00 PM coffee can still be active deep into the night,
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and studies show that it doesn't just last, it shifts sleep.
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So even a few hours before bed can actually delay your body's
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melatonin release and cut your total sleep time by over an hour.
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chris: Absolutely right.
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And of course, broken sleep then feeds straight back into tomorrow's crash, which
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you'll probably fix with more caffeine.
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And of course, off we go again, and again, and again.
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Matt: And the loop continues.
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So the afternoon coffee isn't just helping the day, is it?
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It might be quietly shaping your tomorrow's slump as well.
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Jen: Yeah.
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And it's worth saying this isn't about willpower.
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You can't out-focus, unfortunately- … a natural drop in cortisol.
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Yeah.
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Rising sleep pressure and a circadian dip all at once, unless
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you are superhuman, of course.
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chris: Absolutely.
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It's such an important point because it's so easy to look
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in the wrong places, isn't it?
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When you're, you know, trying to understand afternoon dips or sleep issues.
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And of course, you've also got variation between people.
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'Cause the dips don't all happen at the same time.
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You've got early risers, natural early risers, they will dip
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earlier, and night owls will dip later, which obviously makes sense.
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But if you think about shift workers, parents, people under
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chronic stress, all experience these dips and dip time differently.
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Matt: Yeah.
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And it's not just that, right?
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So you get older adults who metabolize caffeine more slowly, don't they?
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And so the same afternoon coffee hangs around longer in their system.
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So age then starts to play into this as well.
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chris: Yeah.
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So true.
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So same drink, different effect depending on whose liver's
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processing it at the end of the day.
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Matt: Yeah.
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So it's not that everyone has the same 2:36 PM crash, very precise time.
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It's just that everyone has a crash, maybe depending on a whole bunch of
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circumstances, you're gonna have some slightly different timings maybe.
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Jen: Okay.
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So what actually helps?
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Matt: Yeah, 'cause this is the part I really want to know, and of course
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you all wanna know it as well.
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What can we actually do about it, guys?
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chris: Yeah.
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So we can look at this in terms of things to do, but importantly, things to not do.
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Jen: Okay, so drinking water early in the day makes a big difference.
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We know that because, like we've said, most people under-drink before
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lunch, so they're already behind.
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chris: Yeah, and eating a balanced diet.
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So a balanced lunch that includes, protein, fiber, fats, that helps to
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smooth that blood sugar, and it reduces the kind of spike and drop effect.
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Matt: Yeah, and sleep is the big one.
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We keep bringing this up, annoyingly so, 'cause Chris is always right.
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But it is the least non-negotiable, right?
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Jen: Ah.
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Sleep, so much power.
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But movement also helps, doesn't it?
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That's one of the most reliable fixes in the moment.
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Even a few minutes of walking, not burpees, as you always
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suggest- … in the office.
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A few minutes of walking does help improve alertness and, like, you don't
15:00
need to do a full workout or burpees, just enough to get your blood moving.
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chris: Yeah, and it might seem like an obvious one, but natural light helps, too.
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So sitting near a window or stepping out for a few minutes in the early
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afternoon, it can really reduce the severity of that incoming dip.
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Jen: And if you can nap or you're lucky enough to have space in your day
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to nap, even just 10, 20 minutes is ideal before 3:00 PM, but keeping it
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under 30 minutes is wise, otherwise you tip into, like, sleep inertia-
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Matt: yeah
15:29
Jen: and come out groggier than when you actually went in.
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Matt: Yeah, we've talked about that before, haven't we?
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At 26 minutes for me, that's my perfect nap time.
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Just putting that out there.
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It's what NASA discovered.
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And I do want to acknowledge, though, that most workplaces, despite the
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26-minute NASA research, is not set up for this sort of professional nap time.
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So the realistic version may well be a walk and some water.
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Jen: And if you need food- Here I am, Captain Sensible.
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Go for protein, fiber, and fats, like yogurt, nuts, hummus, fruit.
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chris: Yeah, and I'm gonna be kinda Captain Miserable here because- … as
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hard as it is to do, you've got to avoid those big sugary hits because-
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Jen: Oh,
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it's
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hard
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chris: you get that spike and drop thing again.
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So, by relying on those biscuits that you keep going to, it means you're
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effectively buying yourself a slightly later version of the same crash.
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Matt: So the biscuit tin, is emotionally supportive, and to be fair, we've got
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posh biscuits, haven't we, on here?
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But psychologically, maybe it's not helping us.
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chris: No, afraid not.
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But another thing on that do, do not do list is the trap of having
16:40
that big afternoon caffeine hit.
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So guzzling a big cup of coffee, it might fix today's kinda mid-afternoon slump,
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but it's at the cost of tonight's sleep, which of course will then directly affect
16:52
tomorrow's slump, and so on and so on.
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Jen: And trying to brute force your way through on pure willpower doesn't
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really work when you're running at a 15 to 25% cognitive deficit.
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Matt: Which might actually be my new favorite excuse.
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"Sorry, I'm operating at my 20%, deficiency today. Please send that to
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me after 4:00 PM. Love and hugs, Matt."
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Jen: But do you know what stands out is how everything we talk about in other
17:22
episodes converges here, so sleep, hydration, caffeine, stress, nutrition.
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chris: That's it, and it makes, the kind of afternoon slump, the
17:32
dip thing, a quite useful signal.
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So if it's severe, it's something upstream is probably off, and it's worth attention.
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Jen: So it's almost like your daily status report from your body.
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So a mild lull means the foundations are holding, but a full derailment
17:46
means something's asking for attention.
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Matt: Which I don't love hearing, if I'm honest, because mine feels
17:53
pretty consistent at this point.
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Jen: But it's not a flaw.
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It's a feature.
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Your body has a natural low point in the day.
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chris: Yeah, and of course, the problem we have now is we've built schedules in
18:05
life that expect peak performance exactly when the biology kinda says otherwise.
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So if you do have the flexibility, the best thing to do is kind of protect
18:14
your mornings for that focus-type work-
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Jen: Mm-hmm
18:17
… chris: and move admin and maybe more menial tasks into the afternoon.
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Matt: Yeah.
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So it's less, what's wrong with me and more why am I trying to do
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spreadsheets at my biological low point?
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Jen: So why do we get afternoon energy crashes?
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chris: It's because four systems converge, circadian rhythm dips, sleep
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pressure rises, cortisol falls, and certain foods amplify the whole thing.
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So together they create this predictable 15 to 25% drop in cognitive performance
18:49
right in the middle of the working day when you really want that performance.
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Jen: And it's not a failure, it's a normal rhythm, and the goal
18:57
isn't to eliminate it, it's to understand it and work with it.
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Matt: So 2:36 PM isn't a personal weakness.
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It's when your cortisol, your temperature, your sleep, pressure, and possibly
19:11
last night's coffee, all walk into the same room at exactly the same time.
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You just happen to be the one sitting in the chair.
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Jen: So that's why.
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That's it for this week.
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Make sure you hit that subscribe button.
19:26
We're unpacking the science behind everyday questions each week.
19:29
And tell us in the comments what questions you'd like us to explore.
19:33
Thanks for geeking out with us.
19:35
But for now, that's it from me.
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Matt: That's it from me.
19:38
chris: And that's it from me.
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Jen: Bye for now.