Persistent Iron Deficiency: Why Your Iron Won't Stay Up and What to Do About It
- Aug 17
- 10 min read
You've been taking iron and your levels have come up a little. Then you stopped and they dropped back down. Or you had an infusion, felt better for a few months, and then the familiar heaviness and brain fog slowly returned. So you've been told to keep supplementing, but nobody has asked why this keeps happening.
Persistent iron deficiency, iron that will not come up and stay up despite appropriate treatment, is one of the most common clinical presentations in women of reproductive age. And it is almost always the result of two things operating simultaneously: too much iron being lost, and not enough being absorbed. Addressing one without the other is why so many women stay stuck in this cycle.
Persistent iron deficiency has two sides. How much you are losing and how well you are absorbing what you replace. Both need to be addressed.
Why Iron Deficiency Is So Common in Women
Iron deficiency is the most common nutritional deficiency globally. In women of reproductive age, menstrual blood loss is the leading cause. Research published in the International Journal of Gynecology and Obstetrics confirmed that women with heavy menstrual bleeding lose five to six times more iron per cycle than women with normal blood loss, resulting in total depletion of iron reserves over time. A 2025 review published in ScienceDirect confirmed that this blood loss adversely impacts physical health, emotional wellbeing, and work productivity independently of anaemia (Munro et al., IJGO, 2023; ScienceDirect, 2025).
The most important point from this research is that most clinical practice treats iron loss as a fixed variable and focuses intervention on replacement. Supplementation and infusions are prescribed. Levels are monitored. When levels fall again, the same treatment is prescribed again. The reason for the ongoing loss is rarely addressed.
The Heavy Bleeding Side
For women with heavy periods, the rate of iron loss through menstrual blood is often greater than they can replace. The iron that is taken in is absorbed, but the net result is still deficient because the loss is outpacing the gain.
The hormonal drivers of heavy menstrual bleeding - oestrogen dominance, low progesterone, and thyroid dysfunction, can actually be addressed. The critical point here is that addressing these drivers reduces blood loss, and reducing blood loss changes the equation of iron balance. Supplementation works significantly better when there is less blood loss to offset.
The relationship between heavy bleeding and iron deficiency also runs in both directions. Iron plays a role in vascular constriction, helping vessels in the uterine lining tighten and slow bleeding. When iron is depleted, this constriction is impaired. Vessels bleed more freely and for longer. Low iron makes periods heavier, and heavier periods deplete iron further. Breaking this cycle requires addressing the hormonal drivers of heavy bleeding alongside iron replacement.
The Absorption Side
Iron absorption is not a simple process of taking a supplement and having it all reach the bloodstream. It is a highly regulated process that depends on the health of the gut environment, the activity of regulating hormones, and a number of nutritional co-factors. When any of these are compromised, iron absorption is impaired regardless of how much you take.
Where Absorption Happens
Dietary iron and supplemental iron are absorbed primarily in the duodenum and upper small intestine. The absorptive cells lining this region take up iron and transfer it into the bloodstream. This process is only possible when the gut environment is in good condition. Chronic inflammation of the gut lining, compromised intestinal integrity, and bacterial overgrowth in the small intestine all directly impair this process.
SIBO and Iron Competition
Small intestinal bacterial overgrowth, or SIBO, is the presence of excessive bacteria in the small intestine, a region that should have relatively low bacterial counts compared to the large intestine. When bacteria colonise the small intestine in significant numbers, they compete directly for the iron arriving from food and supplements.
Iron is a growth substrate for many bacterial species. Bacteria require iron for their own metabolic processes, and in the presence of SIBO, a significant proportion of ingested iron is sequestered by bacteria before it can be absorbed by the body. This is one of the most specific and most overlooked mechanisms driving persistent iron deficiency in women who also have digestive symptoms.
Research from the REIMAGINE study identified that Escherichia coli and Klebsiella pneumoniae are increased in the small bowel microbiota in patients with SIBO and correlate with the severity of abdominal pain, diarrhoea, and bloating. These are among the bacterial species with high iron requirements, providing a direct mechanistic explanation for iron competition in SIBO.
Women with SIBO often describe bloating immediately or shortly after eating, nausea, reflux, and unpredictable bowel habits alongside their iron deficiency. The connection between these digestive symptoms and iron is rarely made in standard clinical assessment. Addressing SIBO through appropriate treatment can meaningfully improve iron absorption and allow supplementation to work effectively.
Hepcidin and Inflammation
Hepcidin is a hormone produced by the liver that acts as the master regulator of iron balance in the body. It controls both absorption of iron from the gut and release of iron from storage. When hepcidin is high, iron absorption is actively blocked and stored iron cannot be released into circulation.
Hepcidin rises in response to two triggers: adequate or excess iron levels, and systemic inflammation. In states of chronic low-grade inflammation, whether from gut dysbiosis, autoimmune activity, or other inflammatory drivers, hepcidin remains chronically elevated and creates a state of functional iron deficiency where iron cannot be properly absorbed or released even when total body iron stores are not severely depleted.
A 2024 study published in Swiss Medical Weekly confirmed that oral iron supplements themselves acutely increase plasma hepcidin concentration, which reduces iron absorption and can lead to intestinal irritation. The research found that providing lower dosages between 40 and 80 mg and avoiding twice-daily dosing maximises absorption. Taking high doses of iron supplements on consecutive days raises hepcidin enough to significantly impair the absorption of subsequent doses, which is why alternate day supplementation is now supported by emerging evidence (Simic et al., Swiss Medical Weekly, 2024; Moretti et al., Blood, 2015).
This has practical implications for how iron supplementation is approached. Higher doses taken more frequently are not necessarily more effective and may actively impair absorption through hepcidin elevation. The goal is not maximum supplementation but optimal absorption, which requires attention to dose, timing, and the inflammatory environment in which supplementation is occurring.
The Ferritin Question
Standard iron testing often measures haemoglobin, which remains within the normal range until iron deficiency is advanced. Ferritin, the protein that stores iron, depletes long before haemoglobin falls. A woman can be significantly iron deficient by ferritin, with real and measurable symptoms of fatigue, brain fog, hair loss, impaired immune function, and restless legs, while still having normal haemoglobin.
Ferritin below 30 micrograms per litre, and in some clinical frameworks below 50, is considered depleted even when haemoglobin is within range. Assessing ferritin rather than haemoglobin alone is the appropriate standard for identifying iron deficiency in its earlier, more treatable stages.
“What I see consistently in clinic is women who have been supplementing iron for years, or cycling through infusions, without anyone looking at why the iron is not staying up. When we look properly, there is almost always a combination of factors: periods that are heavier than they should be because the hormonal drivers have never been addressed, a gut environment that is not absorbing iron effectively because of dysbiosis or bacterial overgrowth, and sometimes hepcidin elevation from chronic inflammation suppressing absorption further. Address all three and iron levels stabilise in a way that supplementation alone never achieves.”
- Gemma Knaap, Naturopath (BHSc Naturopathy, Certified Natural Fertility Educator, Gut Microbiome Analyst)
Southernwood Apothecary & Clinic
The Role of Infusions
Iron infusions are an effective and sometimes necessary intervention, particularly when levels are critically low, symptoms are significantly affecting quality of life, or oral supplementation has not been tolerated. The relief that comes from restoring iron rapidly is real and meaningful.
What an infusion does not do is address why iron keeps depleting. If heavy periods are the primary source of loss, the infusion buys time without changing the trajectory. If gut absorption is impaired due to SIBO or chronic inflammation, the same applies. Understanding why iron keeps falling is what changes the long-term outcome, and that investigation is worth pursuing before or alongside the decision to have an infusion.
What a Comprehensive Approach Looks Like
A thorough approach to persistent iron deficiency begins with ferritin rather than haemoglobin, establishes the degree of depletion accurately, and then investigates both sides of the equation.
• Menstrual loss: assessing the degree of heavy bleeding, investigating the hormonal drivers of that bleeding including oestrogen dominance, low progesterone, and thyroid dysfunction, and addressing those drivers alongside iron replacement.
• Gut absorption: assessing gut health for evidence of SIBO, dysbiosis, intestinal permeability, and inflammatory markers that might indicate hepcidin elevation. Where SIBO is suspected, breath testing provides the most direct assessment.
• Supplementation strategy: selecting the most bioavailable form of iron, considering timing in relation to food and other supplements, taking with vitamin C to enhance absorption, and considering alternate day dosing to minimise hepcidin elevation.
• Inflammatory load: assessing and reducing systemic inflammatory drivers that elevate hepcidin and suppress absorption.
When both sides of the equation are addressed, iron levels tend to stabilise in a way that supplementation and infusions alone do not achieve. The goal is not just to restore iron. It is to build a physiological environment in which iron stays up.
When Iron Stays Low
If your iron has been persistently low and nobody has looked at why, that investigation is available and worth pursuing. The drivers are almost always identifiable when the right questions are asked and the right tests are ordered. And the difference between managing iron deficiency and actually resolving it is almost always found in understanding what is driving it. If this sounds like you, I'd love to help. Appointments are available in person in Albany or via Telehealth from anywhere in Australia.
Frequently Asked Questions
Why does my iron keep dropping even when I supplement consistently?
Persistent iron deficiency despite supplementation almost always has two contributing factors. The rate of iron loss exceeding the rate of replacement, most commonly through heavy menstrual bleeding, and impaired absorption through a compromised gut environment. Bacterial overgrowth in the small intestine competes directly for dietary iron. Chronic gut inflammation impairs the absorptive surface. And elevated hepcidin from systemic inflammation actively blocks absorption at the gut wall. Addressing both the loss and the absorption is what changes the outcome.
What is ferritin and why does it matter more than haemoglobin?
Ferritin is the protein that stores iron in the body. It depletes long before haemoglobin falls, meaning a woman can have significant iron depletion with real symptoms of fatigue, brain fog, hair loss, and impaired immunity while still testing within the normal haemoglobin range. Ferritin is the appropriate marker for identifying iron deficiency in its earlier stages. A ferritin below 30 micrograms per litre is considered depleted, and many clinicians use a threshold of 50 for optimal function.
Can SIBO cause iron deficiency?
Yes. Bacteria in the small intestine actively compete for dietary iron, which is a growth substrate for many bacterial species. In the presence of small intestinal bacterial overgrowth, a significant proportion of ingested iron is sequestered by bacteria before it can be absorbed by the body. Women with persistent iron deficiency who also have digestive symptoms including bloating after meals, nausea, or reflux may benefit from assessment for SIBO as part of their iron management.
Does heavy menstrual bleeding always cause iron deficiency?
Not necessarily, but research shows that women with heavy menstrual bleeding lose five to six times more iron per cycle than women with normal blood loss. When this loss is combined with impaired absorption, the deficit compounds quickly. And low iron itself impairs vascular constriction in the uterine lining, making periods heavier. This self-perpetuating cycle is one of the reasons iron deficiency and heavy periods are so often found together and why both need to be addressed simultaneously.
What is hepcidin and how does it affect iron absorption?
Hepcidin is a liver hormone that regulates iron balance by controlling absorption from the gut and release from storage. When hepcidin is elevated, iron absorption is actively blocked. Hepcidin rises in response to adequate iron levels, but also in response to systemic inflammation. Chronic inflammation from gut dysbiosis, autoimmune conditions, or other sources keeps hepcidin elevated and suppresses iron absorption even when supplementation is consistent. High-dose oral iron supplements also transiently elevate hepcidin, which is why alternate day supplementation tends to produce better absorption than daily high doses.
Are iron infusions the right answer for persistent iron deficiency?
Iron infusions are effective at rapidly restoring levels and are sometimes necessary, particularly when deficiency is severe or oral supplementation has not been tolerated. The limitation is that they do not address why iron keeps depleting. If heavy bleeding is the primary source of loss, or if gut absorption is impaired, levels will continue to fall after the infusion. Understanding and addressing the drivers of ongoing deficiency changes the long-term outcome in a way that infusions alone cannot.
Can a naturopath help with persistent iron deficiency?
Yes. A naturopath assesses both sides of persistent iron deficiency: the rate of loss through menstrual bleeding and the hormonal drivers behind it, and the gut health factors affecting absorption including SIBO, dysbiosis, intestinal permeability, and inflammatory load. Treatment is targeted at both simultaneously. In person consultations are available in Albany WA and Telehealth consultations are available across Australia.
About the Author
Gemma Knaap is a naturopath specialising in women's hormonal health, gut health, fertility, and reproductive wellbeing. She holds a Bachelor of Health Science in Naturopathy and is a Certified Natural Fertility Educator and Gut Microbiome Analyst. In person consultations are available at her Albany, WA clinic. Telehealth consultations are available across Australia.
References
Munro, M.G. et al. (2023). Heavy menstrual bleeding, iron deficiency, and iron deficiency anemia: Framing the issue. International Journal of Gynecology and Obstetrics, 162(S2), 4-13. https://doi.org/10.1002/ijgo.14943
ScienceDirect. (2025). Ferritin before hemoglobin: Impact of abnormal uterine bleeding on quality of life. https://www.sciencedirect.com/science/article/pii/S2949838424000410
Simic, S. et al. (2024). The magnitude of the plasma hepcidin response to oral iron supplements depends on the iron dosage. Swiss Medical Weekly, 154, 3635. https://smw.ch/index.php/smw/article/view/3635
Moretti, D. et al. (2015). Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood, 126(17), 1981-1989. https://doi.org/10.1182/blood-2015-05-642223
AGA Clinical Practice Update on Management of Iron Deficiency Anemia: Expert Review. (2024). Clinical Gastroenterology and Hepatology. https://www.cghjournal.org/article/S1542-3565(24)00410-5/fulltext
Gut Microbiota for Health. (2025). Microbiome highlights from Digestive Disease Week 2025. https://www.gutmicrobiotaforhealth.com/microbiome-highlights-from-digestive-disease-week-2025/
Gut Microbiota for Health. (2023). Certainties and uncertainties of SIBO. https://www.gutmicrobiotaforhealth.com/certainties-and-uncertainties-of-sibo/
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