Jen: Welcome to the So That's Why podcast, where we unpack the
science behind everyday questions.
I'm Jen.
Matt: I'm Chris.
And I'm Matt.
Jen: Okay.
A quick one to kick us off.
What is the most common nutritional deficiency on the planet?
Matt: B12.
Chris: Vitamin D.
Jen: Okay.
It's not B12 or vitamin D. It's actually iron.
Around a quarter of the world is anemic, and roughly half of those
cases come down to one mineral that most of us barely think about.
Um, so today we are gonna talk about why do we need iron and why
are so many of us running short?
Matt: Yeah, a quarter of the world, and yet iron isn't the one
trending on TikTok at the moment.
Magnesium is currently the one getting all the spotlight.
Vitamin D obviously gets the headlines, and iron's just sort of quietly out
the back doing all the heavy lifting.
Chris: Which is the irony with iron.
Matt: Yeah.
Chris: I'm so
sorry.
Jen: Love the dad joke.
Matt: The iron-y.
Chris: In fact, I'm just gonna go.
I'm done.
I'll get my coat.
Um, so iron is the reason all of those other items we mentioned can
function at all, the vitamin D, the B12, w- magnesium, whatever.
Without iron, the oxygen we're breathing would never reach the
s- a single cell in our body.
Jen: So that's the bit that always gets me.
Every breath you have ever taken has been delivered to your body by iron,
and almost no one ever thinks about it.
Matt: Yeah, so in marketing terms, I guess iron has got a bit of an image problem.
Jen: Yeah.
Matt: Uh, it's got, yeah, it's got the most important job.
Uh, it's got no recognition.
It sounds, I, I, it sounds like y- every IT department I
guess I've ever worked with.
Jen: All the IT departments are like, "Yes."
Matt: Yes.
Jen: Finally.
Matt: That's my suppli- that's my mineral.
Right.
Gr.
Well, sh-
Chris: we got a shout-out.
IT finally got a shout-out on the show.
So
Jen: back to iron.
Chris: Yeah, so hopefully by the end of this episode, if we actually do
our job, you'll know exactly why, um, low iron makes you tired in a way that
no amount of coffee will fix, and why some people need significantly more
than others without ever realizing it.
Jen: So it's always helpful, isn't it, to put, like, the scale of this into context.
So the World Health Organization, they estimate that around 25% of
the global population is anemic.
So that's roughly two billion people.
Um, and iron deficiency is responsible for about half of those cases of anemia.
Chris: It's massive, isn't
it?
Matt: It's huge.
Yeah, two billion people.
I mean, that's an enormous number of people.
Oh, it is something that most of us barely think about.
I don't even know how you define two billion.
I know.
Do you know what I mean?
I can't imagine the number in my head.
Jen: I know.
Chris: Yeah.
It tends to, uh, creep in gradually when it comes to iron, so most
people don't notice that they've been running on reduced capacity
for months, sometimes even years.
Jen: So where it gets really interesting clinically is a category
called iron deficiency non-anemia.
So your stores are depleted, you feel rough, um, you feel tired,
you've got brain fog, you're slow to recover from exercise.
I feel like maybe it's describe- … describing myself.
Um-
Matt: I
was thinking the same thing.
I just put it down to age, but apparently not.
Jen: Yeah, but, you know, your hemoglobin in these cases, it hasn't fallen far
enough yet to trigger a clinical anemia diagnosis on a standard blood test.
Matt: Which is crazy, isn't it?
So people can be properly low on iron, feeling rubbish for it, I, I,
I'm not talking about you, Jen, but definitely me, uh, and the test still
sort of tells them that they're fine.
Jen: Mm-hmm.
Chris: Yeah, and it's a really important, uh, thing to distinguish here.
So the standard test for iron measures hemoglobin, which is
actually the last thing to fall.
So the true early warning sign is ferritin, which is your iron
storage marker, and unless your doctor specifically asks for it,
it often doesn't get checked.
Jen: Okay.
So a bit, for a bit more context, between 25 and 40% of pregnant women in the UK
and Ireland are running low on iron.
Um, you know, women of reproductive age, they lose somewhere between, like, 10 and
30 milligrams of iron per menstrual cycle.
And those numbers that I've mentioned, they don't even touch,
like, athletes or plant-based eaters, where the rates climb higher again.
Matt: Yeah, which kinda makes me wonder how many people are putting
persistent fatigue down to just being busy or not sleeping well,
when there's a perfectly measurable mineral underneath this whole thing.
Mm.
Chris: I suspect it's a lot of people- Yeah … to be fair.
And, um, of course, fatigue is arguably the most reported symptom of low iron,
and it's the easiest to miss because everybody has it some days, don't we?
You know, we all have days when we, we feel tired.
Um, but the pattern people miss is when it doesn't seem to improve, so
no amount of sleep seems to restore you or it feels like the caffeine
stops doing what it used to do.
Jen: Okay.
So what's actually… what is iron actually doing in the body?
That's what people probably wanna know.
So about 70% of all the iron in your body is locked in two proteins, hemoglobin
in your red blood cells and myoglobin in your muscles, and both have one
job, and that is moving oxygen around.
Chris: That's right.
And hemoglobin, or he- each hemoglobin molecule carries four iron atoms kinda
tucked inside it, and then each one grabs a single oxygen molecule in the lungs,
holds onto it through the journey, and it lets it go where it's needed in the body.
So if you multiply that across the trillions of red blood cells in your body,
you've got this kind of oxygen, I guess, like, courier service running constantly
in every direction, never stopping.
Matt: Yeah.
So I, I guess iron's basically the postmaster in the postal system, isn't it?
Without it, the oxygen never gets sorted, never gets delivered, and
never makes it to the front door.
Chris: We could call it Iron Man, but I, I guess that's already gone.
Someone beat
Matt: us to the punch.
Yeah.
I like that.
This is the Iron Man episode- Yeah … uh, for the purposes
of search engine optimization.
Brilliant.
Jen: Okay.
So when your iron levels drop, um, the system, your body, it doesn't stop.
Obviously, it just slows down.
So your red blood cells get made smaller 'cause they've got less hemoglobin packed
in, so then each one carries less oxygen.
So your body is still delivering, it's just sending half-empty parcels.
Chris: Yeah.
That's right.
And, and that's what causes the kind of symptoms to cascade.
So less oxygen reaching the brain means poorer focus and slower thinking.
Less reaching the muscles means, uh, breathlessness and fatigue, and less
reaching the immune cells means a, a kind of, a slower recovery from any infection.
Jen: Mm.
Matt: Yeah.
Which would explain why low iron symptoms feel so scattergun, don't they?
You've got the brittle nails, the brain fog, the racing heart all at
once, and it's, I think it's easy to put that kind of thing down to
different things when it's actually one mineral underneath all of it.
Jen: It is.
And you mentioned brain fog, Matt.
Uh, so that actually does deserve its own moment because the research is striking.
There was a 2023 systemic review of 13 randomized controlled trials.
So they found that giving school-age kids iron supplements significantly improved
their intelligence because it impacted attention, concentration, and memory.
So there was measurable cognitive gains from correcting just one nutrient.
Chris: That's it.
And we see the same, um, pattern in brain scans.
So areas of the brain involved in reasoning and problem-solving,
they massively depend on iron.
So when these iron levels are low, the performance drops.
Matt: Yeah, and that's the story from the body side of it, isn't it?
But when we zoom out to diet, it gets a… it seems to get a lot more complicated.
Iron doesn't all come in the same form.
There are two types, aren't there?
There's heme, there's non-heme iron, and that difference really matters, especially
if you're on a plant-based diet.
So can you guys explain that a little more?
Chris: Sure.
So heme iron comes from animal sources, so things like, uh,
meat or fish and shellfish.
And heme iron's absorbed at roughly 15 to 35% kind of absorption rate, um, almost
regardless of what else is on your plate.
But non-heme iron is different.
It comes from plants, um, eggs, fortified foods, but this absorbs much lower,
so it could be anywhere from 2 to 20%, and it's massively influenced by what's
around it, so what's on your plate.
Jen: And the, the reason for the difference is structural, so a bit of a…
would this fall in chemistry, biology?
Bit of both.
So heme iron sits inside a porphyrin ring, and that protects it through digestion,
whereas non-heme iron, that's got to be converted in your gut before it can
be absorbed, which makes it much more vulnerable to anything that interferes.
Matt: Yeah.
So heme iron is more easily absorbed while non-heme iron needs a bit more help, uh,
depending on what else is in the meal.
Chris: Yeah.
That's a really good way of putting it and a good distinction.
And the biggest factor affecting non-heme iron is phytates.
So phytates are found in whole grains, they're found in nuts, in,
in legumes, and these phytates can reduce iron absorption by over 50%.
But there are other things.
So calcium can impact it, as well as compounds in tea and
coffee, and some proteins.
These things can all push that absorption down further.
Jen: But on the flip side, vitamin C is like a standout enhancer, so that
helps convert non-heme iron into a form that your gut can absorb more easily.
So even something as simple as, like, a squeeze of lemon on a lentil
dish or a glass of orange juice with a fortified breakfast cereal
can make a noticeable difference.
Matt: Yeah.
So if non-heme iron is harder for the body to absorb, vitamin C is really what
helps it m- helps make it more available.
Jen: Mm.
Chris: That's right.
And there's a, an interesting bit of biology.
I think it's interesting anyway.
Jen: Me too.
Me too, Chris.
Chris: Um,
Matt: well done you two.
Chris: We need to just go, you know.
Yeah.
Stick our lab coats on.
Yeah, get on
with it.
Jen: Geek out in the lab.
Chris: Um, so the body tightly regulates non-heme iron.
So if your b- uh, iron stores are full, absorption naturally drops off.
But heme iron is less tightly regulated, which means the iron balance is
something to think about over weeks and months rather than a single meal.
So it, it's not the same depending on those two forms of
iron that you mentioned earlier.
Jen: Mm. And that's where day-to-day habits start to
matter as well, don't they?
So tea and coffee are worth flagging here, as Chris said.
Um, so the polyphenols and the tannins, they bind to iron and
reduce how much is absorbed.
Even a cup within an hour of an iron-rich meal can noticeably reduce its uptake.
Matt: Yeah, which is… immediately complicates life
if you're British, doesn't it?
Because the post-meal cup of tea is, well, it's a national institution.
It is in our house anyway.
Jen: Yeah, absolutely.
Chris: Yeah, don't fear, Brits.
It's not too catastrophic, so there's plenty of room to
enjoy your, uh, cup of tea.
Jen: Yay.
Chris: It's just a case of considering the timing.
So, um, it's ideally just don't have it in the same hour as a meal that's
meant to be topping up your iron.
So give the iron time to absorb and then enjoy that lovely cup of British sh- tea.
Jen: Well, it's worth us talking about who needs to pay particular,
um, attention here 'cause the variation between groups is huge.
So adult men, for example, under the age of 50 need around about
eight milligrams of iron a day.
but then women of reproductive age need about 18 milligrams a
day, and then pregnant women, they need about 27 milligrams a day.
So we're talking about more than a, a threefold difference depending
on what life stage you're in.
Matt: Yeah, and that gap I think is bigger than I would've thought, if I'm honest.
Jen: Mm.
Matt: Uh, most general health advice gets pitched in the, at the average, isn't it?
Jen: Yeah.
Matt: Um, but iron really feels like one of those nutrients where average
perhaps doesn't really mean that much.
Jen: Mm.
Chris: No, that's it.
And the, the… You're right, the average, it just doesn't
cover those different groups.
Um, and I'd say pregnancy, well, without a doubt, is the most demanding window.
So the total iron requirement across the entire pregnancy is about one gram.
Um, so that's roughly 360 milligrams goes to the baby, mostly in the third
trimester, and about 450 milligrams is used to expand the mother's blood volume.
And in fact, did you know, fact fans, that the mum's blood volume increases
by about 30% to 50% during pregnancy?
Jen: Wow.
Matt: Wow.
That's a
Jen: lot, isn't it?
Matt: That is a lot.
I wouldn't have guessed that.
And so with the added need, it's fair to say pregnant ladies don't
usually get enough iron then, I'm guessing, solely from their diet.
Mm.
Chris: No.
That's right.
So the typical diet provides about 15 milligrams of iron per day, and we're
talking about a requirement, as Jen said, of about 27 milligrams per day.
So that's why routine supplementation in prenatal vitamins is recommended
a- and absolutely essential.
Jen: And just to build on that, a baby actually starts building up iron stores
in those, the final three months of the pregnancy, which then sustains them for
the first four to six months of life.
So in a very real sense, the foundation for early infant development is
being laid down even before birth.
Matt: That's a properly impressive bit of biology, isn't it?
Mm. Um, when you think about it, all that buffering before
the baby's even been born.
Chris: It really is a bit, let's be honest.
It, it blows your mind, doesn't it?
Jen: Yeah.
Matt: Yeah.
In so many ways.
Chris: The amazing… The amazing thing about
Matt: it.
Now, that bit of biology I found interesting.
Chris: Just
that
one.
Jen: We're converting him.
Matt: Just,
just that one.
Jen: We're converting him slowly.
Just that one bit.
Chris: That one bit.
Jen: That
one piece.
Chris: Yeah.
Uh, so moving around, so athletes are another group, um, worth highlighting
here when it comes to iron, and it's particularly female athletes actually.
So they lose iron through sweat, through impact-related, uh, bled r-
uh, red… I think I said bled rud, so.
Yeah.
I mean red blood cell.
You
Jen: were, you were
Chris: on
Jen: the right line, weren't you?
Chris: Um, so red blood cell damage in the feet during running, for
example, and through low-level gastrointestinal micro-bleeding from
sustained training, which I know-
Jen: That sounds horrendous.
Chris: It does, but you know, look it up.
It, it's surprisingly common and pretty painful.
Um, and that's where iron deficiency without anemia becomes a real performance
issue with those kind of factors.
Mm.
Jen: And so we've mentioned it briefly, but then we get to, like, plant-based
diets, and they change the picture a bit.
And this is where things get really practical because non-heme absi-
iron absorbs less efficiently.
Um, so ve- vegans and vegetarians, they need to consume about
80% more iron to meet the same requirements as someone eating meat.
So then a vegan woman of reproductive age isn't aiming
for, like, 18 milligrams a day.
She's more, like, aiming for 32 milligrams a day.
Matt: Which is a meaningful jump.
Jen: Mm.
Matt: Um, and I suppose the real question is whether people actually adjust for
that in practice, or is it something maybe that gets missed in the day-to-day eating?
Mm.
Chris: Yeah.
So data tells us that it does get missed very often.
So studies on v- uh, vegetarian and vegan iron status show high rates of depleted
iron stores compared to omnivores, which is, I guess, no real surprise.
But importantly, not higher rates of clinical anemia, believe it or not.
Matt: Mm.
Chris: So what you tend to see is the body compensating, so it's
working harder to maintain levels.
But this does require a bit of awareness, and the main message is iron levels are
very simple to control regardless of diet.
But you do need to give some consideration to the actual iron intake and all
those factors that affect absorption.
Jen: And then just to widen the lens a bit, children between, um, six to…
Six months and two years, they're another group where iron really matters.
So growth is rapid, isn't it, in that period.
Mm. Um, breast milk is naturally low in iron, and that's a window where
deficiency in infancy has been linked to longer term cognitive effects.
So it's worth being quite deliberate about iron-containing foods at that stage too.
Matt: Yeah.
So if someone's listening and wondering whether, you know, they should
actually do something about their iron, maybe you're listening, maybe
that's the question you've got now.
Mm. Where's the best place to start?
Jen: Okay.
So the best starting point is a blood test, but not just any blood
test, a blood test that includes ferritin, not just hemoglobin.
So that's the most useful single marker, um, because it tells you
whether your stores are actually depleted, not just whether you've
crossed the line into anemia.
Chris: Yeah.
And from a food perspective, um, the highest density plant sources of iron
are cooked spinach, uh, lentils, tofu, uh- Soybeans, pumpkin seeds, and many
foods are fortified with iron, of course.
Mm. For seafood eaters, uh, oysters, mussels, and shellfish are rich sources.
And for meat eaters, it's fair to say red meats are pretty well
known as, as being high in iron.
Jen: Yeah.
Matt: Yeah.
And also the absorption pairing we talked about earlier, vitamin C with non-heme
iron, I think is also quite important.
Jen: Exactly.
So it's the simple things like make it… that make a difference, like a lentil soup
with a squeeze of lemon, a spinach salad with orange segments, um, a fortified
cereal with like a small glass of orange juice, and even cooking acidic dishes
like tomato sauce in a cast iron pan.
That can contribute because iron leaches from the metal into the food.
Chris: Yeah.
And, um, back to supplements here.
So if a supplement is, is needed, timing's really important with iron.
Uh, so as we mentioned earlier, it's best to avoid things like tea and
coffee within an hour of consuming iron.
And actually, iron's one of the few nutrients that it's best
to take on an empty stomach.
Uh, but of course, the issue in supplements is iron's often contain,
uh, combined with other nutrients too, that are best taken with food.
So it's never easy.
There's always a bit of a, a counterbalance.
So I'd say as a, a general rule of thumb, take iron in the morning because
that's the best time for its absorption.
Absorption tends to be highest because of that overnight fast.
Matt: Yeah.
I've seen alternate day dosing come up as well, right?
So research suggesting it might improve absorption, um, and reduce side effects
compared to, uh, everyday dosing.
Jen: Yeah, that's right.
So daily iron triggers a hormone called hepcidin, which down regulates absorption.
So spacing, um, taking your iron supplement every other day, that allows
hepcidin to settle so absorption can then recover ready for the next dose.
And it's especially useful if someone struggled with like constipation
or stomach upsets on a daily dose.
Chris: So one important caveat here, and I'm sorry to do the kind
of Captain Sensible bit, but on, in this case- … it, it's really
important when it comes to iron.
So before taking a kinda high-dose iron supplementation routine, you should
really discuss it with a healthcare professional first, because iron's
one of the few nutrients where excess really is actively harmful, and it's
particularly with people with conditions like hereditary hemochromatosis, where the
gut absorbs far more iron than it should.
Jen: Iron's so important, isn't it?
I know we've talked in a previous episode about magnesium driving over, like, 300
enzymatic reactions in the body, but iron's even more upstream than that.
Does… It, it determines, you know, whether oxygen gets to the cells where
all those reactions are happening.
So without iron, the rest of the chain just doesn't function at full capacity.
Chris: Yeah, you're absolutely right.
And, and that's why iron deficiency shows up across so many systems at once.
So the fatigue, the brain fog, the brittle nails you mentioned, the breathlessness,
the slow recovery, that… All the same underlying issues showing up in
different tissues be- because of iron.
Jen: And that's also why correcting iron status when it is the cause can
transform people's lives, 'cause he- people often describe it as, like, the
light's coming back on, because every system that depends on oxygen delivery
suddenly has the resources it needs again.
Matt: Yeah, so the takeaway is that not all tiredness has the same cause.
Sleep, stress, um, and screens obviously get a lot of attention,
and, and you could argue rightly so.
But sometimes the underlying piece is biochemical, um, and it's worth,
I think, staying open to that.
Jen: So why do we need iron?
Because every cell in your body depends on oxygen, and iron is what delivers it.
It's not the most fashionable nutrient, but it might be the most foundational.
Matt: Yeah, and possibly the most quietly common deficiency on the planet, uh, doing
one of the most important jobs in our body, and it gets very little attention.
Um, and I'm sure I, I will find it at some point, uh, a metaphor for life.
I'm sure there's one in
Chris: there somewhere.
I'm sure you could find one.
Mm-hmm.
And, uh, with iron, a key message from us is, for most people, it's very
manageable with a bit of consideration.
Mm. So iron-rich foods, vitamin C as a partner, that awareness
around tea and coffee timing, and a ferritin check if symptoms persist.
They're the key things to keep a check.
Jen: So that's it for this week.
Hit subscribe wherever you're listening or watching, and drop
your question in the comments.
We really do read them.
Thanks for geeking out with us, but for now, that's it from me.
Chris: That's it from me.
And that's it from me.
Jen: Bye for now.