Low Iron? Why an Iron Supplement Isn't Always the Answer

A client came to me at [44] with a ferritin of [12] and a full year of iron tablets behind her. Every single morning, religiously. Her ferritin had barely moved. Her digestion was wrecked , constipated, bloated, and faintly nauseous every day, and she was still exhausted. And in that entire year, not one person had asked the two questions that actually mattered: why was she losing iron, and could she even absorb what she was swallowing? [Amend details as needed.]

This is one of the most common patterns I see when people start looking for a low iron supplement. And the answer is genuinely fascinating, so let me take you through it properly, because once you understand it, you will never look at a low iron supplement or an iron tablet the same way again.

Iron deficiency is a symptom, not a diagnosis

Let's be clear about this first, because it matters more than everything else in this article.

“Low iron” tells you the level. It does not tell you why. And iron does not simply evaporate; either you're losing it, not absorbing it, or not taking enough in. Usually the first two.

The common causes: heavy periods (wildly under-acknowledged), pregnancy, coeliac disease, H. pylori infection, autoimmune gastritis, low stomach acid, long-term PPI use, gastrointestinal blood loss, and genuinely inadequate intake.

This is why unexplained iron deficiency needs proper medical investigation, not a supplement bought off a shelf. In adults it can be the first sign of coeliac disease or bleeding in the gut, including bowel cancer, which is exactly why NICE recommends investigating the cause rather than simply correcting the number. Please see your GP first. Everything in this article sits alongside that, never instead of it. And if you have been prescribed iron, do not stop taking it on the strength of a blog post, mine included.

Take Bryan Johnson, who spends millions measuring everything about his body. He lived with chronically low ferritin for over eleven years before anyone worked out why. It turned out to be autoimmune gastritis, his immune system attacking the stomach cells that make the acid he needs to absorb iron in the first place. Eleven years of a number nobody chased. If it can be missed in the most measured man alive, it can be missed in you.

The gatekeeper nobody mentions: hepcidin

Stay with me, because this is the bit that explains everything.

Your body has a hormone called hepcidin, made in the liver, and its job is to control how much iron gets in. Think of it as a gatekeeper standing at the doorway of your gut wall. When hepcidin is high, the gate closes and iron simply does not get through, no matter how much you swallow.

And what raises hepcidin? Inflammation. Chronic, low-grade inflammation, the kind that comes with dysbiosis, an autoimmune condition, obesity, infection, or just a body under sustained strain, tells hepcidin to lock the gate. It is actually an ancient defence: bacteria need iron to grow, so when your body senses a threat, it hides the iron away.

Which means if you are inflamed, you can take iron every day for a year and barely move the needle. Not because you didn't try. Because the gate was shut. Do you see what I mean? The tablet was never the problem. The terrain was.

The discovery that changes how you should take it

Now here is the part that genuinely made me sit up when I first read it and that most people, including plenty of clinicians, still haven't caught up with.

When you take a decent dose of iron in the morning, your plasma iron rises. Your body notices. And hepcidin goes up in response, closing that gate. The problem is that the gate stays shut for a while. Research has shown that suppression of iron absorption can last as long as 48 hours.

So if you take iron again the next morning, the way almost every packet tells you to, you are dosing straight into a closed gate.

Randomised trials confirmed exactly this. Taking iron on alternate days, in a single morning dose, produced significantly higher fractional and total absorption than daily dosing. Daily and split dosing raised hepcidin and reduced absorption from subsequent doses. A later trial found alternate-day dosing also triggered fewer gastrointestinal side effects and, at six months, less iron deficiency.

The counterintuitive takeaway: taking iron less often can get more iron into you, with less digestive misery. Standard advice has been slow to catch up. But please don't rewrite your own prescription on the strength of this; take it to whoever prescribed it and ask.

Your gut has more to do with this than you'd guess

Unabsorbed iron doesn't just vanish

Here's the uncomfortable part. Iron, your body doesn't absorb travels on into your colon, where it becomes food for the wrong bacteria. Iron is a growth factor for many pathogenic species, so unabsorbed iron can shift your microbiome in an unhelpful direction, feed inflammation, and cause exactly the constipation, bloating and nausea that make people give up on iron in the first place.

Which produces a genuinely vicious circle: inflammation raises hepcidin, hepcidin blocks absorption, unabsorbed iron feeds dysbiosis, and dysbiosis drives inflammation. Round and round. And the standard response is to prescribe more iron.

The probiotic with actual evidence

This is where it gets hopeful. One specific strain, Lactiplantibacillus plantarum 299v, has been repeatedly shown to increase non-haem iron absorption across fruit drinks, meals and freeze-dried capsules in women of reproductive age. In iron-deficient female athletes, taking it alongside 20 mg of iron improved iron status more substantially and more rapidly than 20 mg of iron alone and improved their vigour. In pregnancy, it reduced the prevalence of iron deficiency and iron deficiency anaemia by 35 weeks.

Strain specificity matters enormously here. This is not “probiotics help iron". This is one strain, with its own body of evidence. Buying a random multi-strain capsule will not reproduce it.

What you eat it with matters as much as what you take

●Vitamin C markedly enhances non-haem iron absorption; squeeze lemon over the lentils and eat peppers with the greens

● Tea and coffee polyphenols dramatically inhibit it, so the iron tablet with your morning tea is close to pointless. Leave an hour either side.

●Calcium competes; don't take iron with dairy or a calcium supplement

●Phytates in grains and pulses bind iron; soaking, sprouting and fermenting genuinely reduce them

●Stomach acid is required to liberate iron from food. PPIs, low acid and autoimmune gastritis all undermine this, and it's rarely considered.

●Haem iron (meat, fish) absorbs far more efficiently than non-haem (plants), which is why vegetarians and vegans need to be more deliberate, not that they can't thrive

So, does everyone low in iron need a supplement?

No. And that is not me being contrarian; that is the physiology.

Some people need iron urgently and medically, and for them a supplement is not optional. But plenty of people with a low ferritin need something else first, or as well:

●The cause fou(SerCoeliacsiously, 2015).nd and dealt with. Heavy periods treated. Coeliac, thoroughly and excluded. H. pylori addressed. Blood loss investigated.

● Inflammation is lowered, so the gate opens and iron can actually land.

● The gut is  Thegut supported, so absorption works and the tablet doesn't feed dysbiosis.

●        The dose and timing corrected , alternate days, single morning dose, away from tea and coffee, with vitamin C.

● Food is genuinely optimised, which is often doing more work than people credit.

And one more, which almost nobody mentions: ferritin can lie. Ferritin is an acute-phase reactant;2015). inflammation pushes it up. So a “normal” ferritin alongside a raised CRP can be hiding a real deficiency. This is why I want to see ferritin, CRP, a full blood count and transferrin saturation together. One number in isolation is a rumour, not a diagnosis.

And the risk in the other direction, which gets almost no airtime: iron overload is genuinely dangerous, and haemochromatosis is one of the most common genetic conditions in people of northern European descent. Supplementing iron without testing is not a neutral act. Never take iron “just in case".case".case".

Key takeaways

●        Low iron is a symptom; the cause must be found, and that starts with your GP

●        Hepcidin, driven by inflammation, decides whether iron gets in at all

●        Daily dosing raises hepcidin and blocks the next dose for up to 48 hours

●        Alternate-day, single morning doses absorb better with fewer side effects

●        Unabsorbed iron feeds the wrong gut bacteria,bacteria, which is why it hurts

●        L. plantarum 299v is the strain with real iron-absorption evidence

Gut

FAQs

My ferritin is low, low, but I'm not anaemic. Does that matter?

Often, yes. Ferritin is your iron savings account, and it empties long before haemoglobin drops. Low ferritin without anaemia is associated with fatigue, hair shedding, breathlessness and poor exercise tolerance. It is worth taking serCoeliacsiously (2015).and worth investigating rather than simply supplementing.

Why does iron make me constipated?

Largely because most of it isn't absorbed and carries on into the colon. Better timing, bseriouslyi(SerCoeliacsiously, 2015). absorption tend to reduce this, as does the alternate-day approach, which triggered fewer gastrointestinal side effects in trials.

Should I take iron every other day, then?

The evidence points that way for many people, but discuss it with whoever prescribed it. Do not change a prescribed regimen on your own.

Can I fix low iron with food alone?

Sometimes, if the losses are modest and absorption is intact. Often not, if you're bleeding heavily or inflamed. Food is the foundation, not always the whole answer.

Does coffee really matter that much?

Yes. Polyphenols in tea and coffee are potent inhibitors of non-haem iron absorption. It's one of the easiest and highest-yield changes there is.

Are vegetarians doomed?

Not at all, just more deliberate. Pair plant iron with vitamin C, soak and sprout your pulses, keep tea away from meals, and test rather than assume.

Conclusion

“You're low in iron; take these” is one of the most common instructions in medicine and one of the least examined. It skips the two questions that decide whether any of it works: why are you low, and can you actually absorb it?

Your body is not being difficult. It is running an ancient, intelligent system for controlling a mineral that is both essential and dangerous. Work with that system, find the cause, lower the inflammation, support the gut, time the dose, and iron starts landing where it belongs.

Tired of being told your numbers are “a bit low, nothing to worry about”? Book a free Health Roadmap, seriously(reactant, 2015). And let's because Wasad thoroughly,And alongside your GP, never instead.

Research & references

Alternate-day vs daily iron dosing, Stoffel et al., two open-label RCTs, The Lancet Haematology, 2017. https://www.thelancet.com/article/S2352-3026(17)30182-5/abstract

Iron raises hepcidin & blocks later doses (Moretti et al., Blood, 2015); suppression of absorption can last up to 48 hours. https://pubmed.ncbi.nlm.nih.gov/26289639/

Alternate-day dosing, fewer side effects, less deficiency at 6 months , RCT, eClinicalMedicine, 2023. https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00463-7/fulltext

L. plantarum 299v increases iron months, absorption (Hoppe et al., double-isotope crossover study, British Journal of Nutrition, 2015. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4594053/