Jen: Welcome to the So That's Why podcast, where we unpack the
science behind everyday questions.
I'm Jen.
Chris: I'm Chris.
Matt: And I'm Matt.
Jen: Okay, so here's one that can sometimes be slightly awkward, but
is actually genuinely fascinating.
Why does alcohol affect people so differently?
'Cause in any group you'll see that one person getting visibly merry
after two drinks, while someone else can go through the whole evening
looking completely unaffected.
Matt: Yep, we've all seen it, that social dynamic that has a different person
responding to alcohol in a different way.
Uh, one who's chatty after half a glass, and then there's one who's treating their
first bottle of wine like it's a warm-up.
And neither of them can really explain why that sort of phenomenon exists.
And I possibly would, would, uh, posit to you that they might not even care.
Chris: Or remember the next day.
Yeah,
Jen: yeah, yeah.
Or either.
Yeah.
Chris: Um, and the answer here actually turns out to be one of the most
individual pieces of biology there is.
So it's shaped by, uh, genetics, by body water content, by sex, age, what
you've eaten, medications, even how you're feeling before that first drink.
Jen: So by the end of this episode, you'll understand why the same few drinks
can land completely differently on two people sitting side by side, and we'll
also look at how drinking patterns are changing and what the science actually
says about lower risk approaches.
Matt: Yeah, and just to say upfront, we're not here to tell
anyone what to do with alcohol.
It's more about understanding why responses differ so
much in the first place.
Chris: Yeah, exactly.
So the science we're looking at is the same for everyone, it's just
with different starting points.
And just to also say, we're only covering the science today.
We're not discussing that one friend that you always have who seems to go missing
every time it's their turn to buy a round.
Jen: Yeah.
Matt: I wonder if there is actually science for that.
Jen: Yeah.
Or if you are that friend, buy a round.
Chris: Sha- Shauli looked at me when you said
that.
Jen: Okay, so let's start with, um, giving this a number to
give it, like, a sense of scale.
So researchers have identified over 400 genomic regions and more than 500
genetic variants linked to how people experience and metabolize alcohol.
Matt: Which again, just wanna meet the person that counts these, right?
So there's over 500 genetic factors influencing how you respond before
you've even had a sip, uh, of the drink.
Uh, which is a lot of va- variation, I think, baked in right from the start.
Chris: Yeah, it really is, and that's why kinda blanket advice doesn't really
fit well when it comes to alcohol.
So two people can have the same drink, or drink the same amount at the same pace,
but still end up with very different blood alcohol levels and, of course, effects.
Jen: Which makes the idea of, "I know my limits" only part- True, because
those limits, they shift depending on sleep, food, stress, age, and
like we said before, medications
Matt: Yeah.
So the same person, uh, on a Tuesday after dinner has a very different sort of
physiological setup, uh, from that exact same person- Mm … on a Friday night
after a long week and possibly no food.
Jen: Mm.
Chris: Yeah, and this whole thing comes down to how the liver
processes the alcohol that we drink.
So alcohol, or ethanol, it gets absorbed through the stomach and the
small intestine into the bloodstream.
Then the liver breaks it down in, in two main steps.
Jen: Okay, so step one, it uses an enzyme called alcohol dehydrogenase,
or ADH, and that converts the alcohol into acetaldehyde.
And acetaldehyde is the nasty part, so it's toxic and carcinogenic,
and it's responsible for a lot of the unpleasant effects of drinking.
Matt: Yeah, like the headaches and the nausea.
They don't really come from the alcohol itself.
It's what the body, um, turns it into, isn't it, while processing it?
Chris: Mm. Yeah, that's right.
And step two uses another enzyme called aldehyde dehydrogenase.
So this is ALDH, and this is to convert the, the acetaldehyde into
acetate, which is then broken down into water and carbon dioxide.
Sorry, I know we're using a lot of, uh, chemically rich names here, and I'm not
quite pronouncing some of them correctly.
But, uh, there you go.
Matt: Yeah, I'm just
glad I'm not supposed to say any of them.
That's-
Jen: But the key, um, point in this process is speed.
So the liver can only process alcohol at roughly one standard drink per hour.
So anything faster than that, it just builds up in your system.
Matt: Yeah.
So it's not that the liver is struggling per se.
It's, you gotta think of it more like a single, uh, road, a single lane road
with traffic sort of building up behind
it.
Jen: Mm-hmm.
Yeah.
Chris: Yeah, pretty much.
It is like that.
And, um, that speed is largely genetically determined, uh, because
those enzymes vary between people.
Jen: So the two main ones are ADH1B, and that enzyme controls how quickly
alcohol becomes acetaldehyde, and then ALDH2, and that controls how quickly
the acetaldehyde then gets cleared.
Matt: Can I just say well done, guys, on the, uh, on the naming
conventions going on here.
Chris: Yeah.
Jen did better than me on that one.
One, one-nil.
One-zero.
Jen: Woo.
Matt: Jen's degree in biochemistry.
Jen: It's finally coming into
play.
Matt: Yeah.
Well done.
So if one, uh, runs fast and one, one of these processes runs fast
and one runs slow, you're gonna get this backlog, aren't you?
You're gonna get, um, a buildup.
Uh, and that's the toxic bit, isn't it, in the middle?
Mm-hmm.
Which sounds, if I'm honest, a little bit unpleasant.
Chris: Yeah, it certainly can be.
And, um, it's especially well-studied in East Asian populations.
And around a third carry a variant of this ALDH2 that doesn't work properly, which
causes flushing even after small amounts.
Jen: And then there's been, there's been lots of other genetic studies that have
confirmed that both of these enzymes, they strongly influence that response.
So it's not psychological, it's the body genuinely struggling to
clear the acetaldehyde efficiently.
Matt: And I guess that would naturally discourage, in theory, heavier drinking
for, uh, a lot of people perhaps.
Jen: Mm.
Chris: Yeah, that's one of the leading theories.
Um, the physical reaction acts as a pretty good built-in deterrent, doesn't it?
Uh, but where people do drink through it, just through kind of stubbornness
or desire- … um, the acetaldehyde exposure carries increased long-term risk,
like particularly with certain cancers.
Jen: So genetics is the foundation, isn't it?
Then everything else layers on top.
Um, I think what, biological sex, that's one of the most consistent
differences, and also a lot of it comes down to body water.
Matt: Yeah, so when people say men and women can't really be
compared drink for drink, unless they're talking about my mum-
there's actually a sort of physiological reason, reason behind that, right?
Jen: Shout out to Matt's mum.
Matt: Yeah, yeah.
Legend.
Chris: Yeah, there is.
I can't comment about your mum.
And I, I've not had a drink with her, but it sounds like it'd be good fun.
Um, but alcohol is water soluble, so it distributes through, um, evenly
through the body in, in its water.
And on average, men have more total body water.
So the same drink in men is of course more diluted than in women.
Matt: Mm.
Jen: And here's another interesting difference.
So men have ADH activity, so the enzyme, in their stomach lining, so they can
metabolize part of the alcohol before it even reaches the bloodstream.
And guess what?
Women don't have that same level of enzyme, so they can't, um, metabolize it.
So for men then, the same glass of wine doesn't enter the system in quite the same
way from the start as it does for women.
Mm.
Chris: Um, yeah, precisely.
And if you combine that with body water differences and you get a
higher blood alcohol concentration from the same intake in women.
Jen: So body composition matters too then, doesn't it?
So muscle holds more water than fat tissue, so higher muscle mass
generally means lower blood alcohol concentration for the same drinks.
Matt: So two people of the same weight can still have very
different responses depending on their actual bodily composition.
So the scales themselves don't really tell the full story.
Jen: Mm.
Chris: Yeah, it's true.
And then we come to age, and age adds another layer.
So we lose roughly 3 to 8% of lean muscle mass per decade after 30.
That's not great, is it?
I'm not, always be these bad stats are good for that.
Um, I'm sure there are benefits of getting older but, you know.
We, we, we bring the facts.
Losing lean muscle mass is one of them, yeah.
Um, and of course, if you lose lean muscle mass, your kinda total body
water is gonna decrease over time too
Jen: Well, I'm joining your joy-bringing party.
The, uh, liver also becomes less efficient, so alcohol
stays in the system longer.
And that's why people often say, don't they, that drinks hit harder
in their 40s than their 20s?
It's a real physiological shift.
Matt: Yeah.
And it also explains why people naturally start moderating as they get older.
Their body actually starts to give some immediate feedback.
Jen: Mm.
Chris: Yeah.
And another consideration with age is that, um, around 80% of adults over
65 are taking at least one medication that can interact with alcohol.
So the situation does become more complex with age anyway.
There's more kind of factors going on.
Jen: Yeah.
And then there's what's happening in the moment, isn't it?
Like food, drink type, and context.
They all matter.
Matt: Yeah.
And there's this idea that I've heard, you know, that you're lining
your stomach before drinking.
My question is, does that actually work?
Chris: It does, and, uh, it works because food slows gastric emptying, which I
appreciate sounds pretty disgusting.
Jen: Very
scientific there, Chris.
Chris: Yeah.
Sorry about that.
That's put me off my lunch now.
Um, but especially meals that have got, um, fats and carbs.
They reduce how quickly that alcohol is absorbed, so it can significantly
reduce peak alcohol blood levels by eating the right kind of food.
Jen: And drink type matters, too.
So spirits absorb faster, while beer and wine are slower.
And then carbonation speeds up absorption, so, like, sparkling drinks, they often
hit faster than people would expect.
Matt: That's an interesting one, isn't it?
So your prosecco at a wedding on an empty stomach is basically
the perfect storm of chemistry.
Jen: Or a way to get people to buy more at the bar, maybe.
Matt: Yeah.
You put… But e- I'm not saying either way.
Chris: So if you have a prosecco on an empty stomach at a wedding
reception, you can say, "This is just a chemistry experiment gone wrong."
Jen: Absolutely.
Chris: Who knows?
Jen: And here's another one, though, that's worth us clearing up.
Um, water doesn't lower blood alcohol levels or speed up metabolism.
It can help with hydration and headaches, but not the intoxication itself.
Chris: Yep, it's true, and studies have shown that, um, water only
has a modest effect on hangovers.
Uh, so the main drivers of inflammation and oxidative stress aren't
really fixed by hydration alone.
Matt: So, you know, the big sort of glass of water fixes everything
strategy is mostly for comfort.
It's not chemistry.
Jen: It's always a good idea, though, isn't it?
Chris: That's right.
I mean, hydration, as we've covered a lot, helps, kind of, everything.
It's the root to- goodness across the board.
Um, and it, course it will make you feel a little bit better, but it doesn't really
address what's going on biologically.
And, uh, that's where medications become another huge factor here.
So as I mentioned earlier, a lot of adults are taking medication, particularly
as they get older, and I think it's around 40% of adults across all ages
are taking something, some form of medication that can interact with alcohol.
And these interactions show up a significant proportion of emergency
admissions related to alcohol.
Jen: Mm.
Matt: That includes pretty common things too, doesn't it?
Like we've got painkillers, we've got antihistamines, sleep
aids, they're all involved.
Chris: Yeah, all of those.
And some amplify sedation, others affect, uh, liver metabolism, some
increase bleeding risk, and all of these effects can happen at actually
relatively low alcohol levels.
Jen: And that ties into how people think about tolerance.
So when someone says they hold their drink well, that's usually functional
tolerance, the brain adapting, so the outward signs are reduced.
Matt: Yeah, but that doesn't mean the internal effects are reduced.
Chris: No.
So the, the brain compensates behaviorally, but the liver
and other organs are still processing that alcohol load.
Jen: And over time, um, reverse tolerance can happen in heavy drinkers too.
So where liver damage reduces metabolism, so small amounts
suddenly have a stronger effect.
Matt: Yeah, so the system can actually swing the other way entirely.
Jen: Mm.
Chris: Yep, it can.
And of course, um, mood and stress also matter a great deal here.
So anxiety, uh, fatigue, low food intake, they all reduce your body's
resilience to the effects of alcohol.
Jen: And those kinds of factors are, they're partly why drinking
patterns are shifting more broadly.
So it's worth us, um, noting that behavior is changing.
So in the UK, around a third of 18 to 24-year-olds don't drink at all.
That's quite big.
Matt: It's a real shift, eh?
Compared to certainly, I would say my generation.
Mm. You know, previous generations.
And there's also this sort of drink less, drink better trend, which seems
to be happening more broadly as well.
Jen: Mm.
Chris: It is, and so many young people seem to just go out at
midnight and, and dance rather than frequent the pubs, isn't it?
Mm. Yeah.
Which is not good for the pubs.
You gotta keep the pubs going.
Or be a thing of the past before too long.
Do you get pubs in the US?
Sorry, US customers, bars.
Yeah.
Matt: Yeah, yeah.
Yeah.
There we go.
Yeah, yeah.
Chris: Um,
Matt: there was a- We should do for pubs what Clarkson did for farming.
Oh, no, wait, he's doing pubs as well now, isn't he?
Jen: Yeah, he is.
Matt: Okay, carry on, Chris.
Sorry.
Chris: Can you explain Clarkson for our listeners?
Matt: Oh, they all know who Clarkson is.
Clarkson's a worldwide phenomenon.
Oh,
Chris: is
Matt: he?
Is he?
Yeah, yeah.
Mm. Clarkson Farms.
Chris: Is, is he our best export?
Matt: I… Best is probably a l- Yeah.
I don't know.
Chris: Yeah.
Anyway.
Sorry, I took us completely off on a tangent.
Yeah, yeah.
But I'll try and bring it back.
So back to Gen Z, there was a 2024 study, and it found that most Gen
Z consumers, they've reduced this alcohol intake in the past six months.
But there is a bit, bit of a change.
So some more recent data has shown some slight re-engagement with alcohol
w- among the Gen Z. Mm. So it's not kind of straight line, that's it.
Uh, there is a bit of a shifting pattern.
But the overall trend is this- Mm … reduced alcohol intake.
Mm. Which is probably not a bad thing.
Jen: No.
But, and across all age groups, I think moderation is increasing,
even if the reasons why differ.
Chris: So the UK guidance recommends no more than 14 units of alcohol
per week spread across several days, and you've also got to
include regular alcohol-free days.
Jen: So to put that into context, that's roughly like six pints or six
medium glasses of wine across the week.
And importantly, there is no completely risk-free level.
It's not.
It's about reducing risk, isn't it?
Not eliminating- Mm … it entirely.
Matt: Yeah.
So the pattern that seems to emerge is pacing, spreading intake, sort
of eating properly, and being aware of personal factors like
medication and mood, for example.
Chris: That's a fair summary, and I think you've definitely taken
my captain sensible hat today-
Matt: I have
… Chris: which is good.
Matt: I, I don't know what's going on, Chris
… Chris: I'll pass the baton.
Jen: Do you like, do you like this role?
Yeah.
Matt: No.
You can have it back for the next one.
Jen: Okay.
So why does alcohol affect people differently?
Chris: It's because it passes through a system that varies
massively between individuals.
So genetics set enzyme speed, uh, body composition sets distribution, age
shifts metabolism, and food, drink type, medications, and mood, they all modify the
response we have to alcohol in real time.
Jen: Which means the same drinks can land completely differently depending
on the person, not because anyone is doing anything wrong, but because
everyone's biology is different.
Matt: Yeah, and it's less about willpower and less about tolerance,
um, but more about individual chemistry doing really what it's built to do.
Chris: Yep.
And once you understand that, a lot of the kind of variation we see
between people, uh, like that you see socially starts to make more sense.
Mm.
Matt: So next time you're out, you're basically watching, uh,
multiple different biological systems sort of reacting in real time.
One big human experiment- … which is actually slightly humbling.
Jen: It is.
And it's a good reminder that normal is a wide range when it comes to biology.
So that's why alcohol affects people differently.
That's it for this week.
Hit subscribe and let us know what we should explore next.
Thanks so much for geeking out with us.
But for now, that's it from me.
Matt: That's it from me.
Chris: And that's it from me.
Jen: Bye for now