The scenario is one I hear regularly. A woman has been diagnosed with iron-deficiency anemia — or is experiencing the classic symptoms of it: crushing fatigue, brain fog, breathlessness on exertion, cold hands and feet, hair loss, pale skin. Her doctor has prescribed an iron supplement. She has been taking it faithfully for months.
Her levels have barely moved. Or they improved temporarily and then fell again. Or they improved on paper, but she still feels exhausted. Or she cannot tolerate the supplement at all — the constipation and nausea are intolerable — and so she stops.
“Keep taking the iron,” she is told. “It takes time.”
But months pass. The fatigue deepens. And nobody is asking the question that actually matters: why isn’t the iron working?
The answer, in most cases, is not that she needs more iron. It is that something upstream is preventing iron from being absorbed, utilized, or retained. Iron deficiency that persists despite supplementation is almost always a downstream symptom of a deeper problem. Until that problem is identified and addressed, the iron will keep failing to fix it.
The Biology of Iron Absorption
Iron metabolism is far more complex than most people — and many practitioners — appreciate. The body does not simply absorb whatever iron you swallow. Absorption is tightly regulated through multiple mechanisms, and any disruption to those mechanisms can create an iron deficiency that has nothing to do with dietary intake.
Central to this regulation is a peptide hormone produced by the liver called hepcidin. Hepcidin is the master regulator of iron homeostasis. When iron stores are adequate, hepcidin rises and blocks the absorption of iron from the gut. When iron stores are low, hepcidin should fall — allowing more iron to be absorbed. In a healthy system, this feedback loop keeps iron levels appropriately calibrated.
But there is one thing that overrides this feedback loop and causes hepcidin to remain elevated even when iron stores are depleted: inflammation. When the body is in a state of chronic low-grade inflammation — which, as I have written about before, is extraordinarily common in my client population — inflammatory cytokines signal the liver to keep hepcidin high. High hepcidin blocks ferroportin, the transporter that moves iron out of gut cells and into the bloodstream. The result is that iron cannot be absorbed, no matter how much is consumed or supplemented. This is what researchers call anemia of inflammation — formerly known as anemia of chronic disease — and it is far more common than most people realize.
The practical implication is stark: if you have chronic inflammation and iron deficiency, supplementing iron without addressing the inflammation is largely futile. The hepcidin wall stays up. The iron doesn’t get through.
The Methylation Connection: MTHFR, FUT2, and Iron
In my MTHFR blog, I wrote extensively about how this common gene variant disrupts the methylation cycle and affects a wide range of biochemical processes. What I did not detail in that piece is the specific impact of impaired methylation on iron metabolism.
The MTHFR enzyme — when it is working efficiently — enables the conversion of folate and B12 into their active, usable forms. These active forms are required not just for neurotransmitter production and cardiovascular health, but for the production of red blood cells and the regulation of hepcidin itself.
When MTHFR function is reduced, the body develops a functional deficiency of B12 and folate even when dietary intake appears adequate. This impairs red blood cell maturation — producing the large, immature cells characteristic of megaloblastic anemia — and it elevates homocysteine, which generates oxidative stress that further impairs the iron-containing proteins involved in oxygen transport.
The MTHFR C677T variant is carried by approximately 40% of people with European ancestry, reducing enzyme efficiency by 40 to 70 percent. For women in this group who are also anemic, treating with standard folic acid — which the impaired MTHFR enzyme cannot properly convert — will not resolve the B12 and folate deficiency driving the problem. Active B vitamin forms are needed, but which specific form is appropriate — whether methylfolate and methylcobalamin, or alternatives such as folinic acid and hydroxocobalamin — depends on the individual’s full genetic picture. This is particularly important in cases of compound heterozygous MTHFR or when slow COMT is also present, where methyl donors can be problematic. This is a clinical distinction that requires proper assessment, not self-supplementation.
A second genetic layer that is almost never discussed in conventional anemia workups is FUT2 — the gene that determines secretor status. FUT2 encodes an enzyme called alpha-1,2-fucosyltransferase, which is involved in the glycosylation of gastric intrinsic factor, the protein produced by the stomach that is essential for B12 absorption in the small intestine. People who carry the secretor variant of FUT2 produce intrinsic factor that is less efficiently secreted, which reduces B12 absorption at the gut level — independently of diet, MTHFR status, or supplement intake. Multiple large-scale genome-wide association studies have confirmed FUT2 as one of the strongest genetic predictors of circulating B12 levels. For a woman who is doing everything right — eating B12-rich foods, supplementing appropriately — and still cannot maintain adequate B12 status, FUT2 secretor status is a critical variable to assess. It explains why some people require higher doses, alternative delivery routes such as sublingual or intramuscular B12, or specific co-support for intrinsic factor function to achieve the same result that others get from a standard oral supplement.
The Cofactors Nobody Talks About
Even when absorption is not the primary problem, iron deficiency can persist because the body lacks the cofactors required to actually utilize iron once it has been absorbed.
Vitamin C is perhaps the most well-known cofactor for iron absorption. It significantly enhances the uptake of non-heme iron from plant sources. But it is consistently under-dosed and under-utilized. Taking a small amount of vitamin C with an iron supplement is not the same as maintaining the cellular levels of vitamin C that support ongoing iron metabolism. In orthomolecular medicine, we understand that therapeutic doses of vitamin C do meaningful work that supplementary doses do not.
Copper is essential for iron mobilization and red blood cell production, yet it is almost never considered in an anemia workup. Copper deficiency produces an anemia that can be clinically indistinguishable from iron deficiency — and long-term high-dose zinc supplementation, which is common in functional medicine circles, can actually deplete copper, worsening the problem it was not designed to solve.
B6 is required for heme synthesis — the iron-containing component of hemoglobin. Without adequate B6, the body cannot incorporate iron into red blood cells even when iron is available. B6 deficiency is far more common than appreciated, particularly in women using the oral contraceptive pill, which depletes B6 significantly.
Riboflavin (B2) is a cofactor for the enzyme that converts iron from its stored ferric form to the ferrous form that can be transported and used. Low riboflavin impairs this conversion, contributing to functional iron deficiency even when ferritin appears adequate.
Gut health underpins all of this. Iron absorption occurs primarily in the upper small intestine, and any disruption to the gut — inflammation, dysbiosis, reduced stomach acid, or intestinal permeability — will impair it. Proton pump inhibitors, commonly prescribed for reflux, reduce stomach acid and meaningfully compromise iron absorption. SIBO and gut dysbiosis create an intestinal environment in which iron uptake is impaired. Gut health is not peripheral to iron metabolism — it is central to it.
The Nutrigenomics Dimension
Beyond MTHFR and FUT2, the genetic landscape of iron metabolism is complex. Variants affecting genes involved in iron transport, storage, and regulation mean that some individuals are genetically predisposed to absorb iron poorly, store it inefficiently, or struggle to mobilize it when needed. Understanding these variants changes both the diagnosis and the intervention.
In my nutrigenomics practice, I see patterns that explain why one woman responds well to a standard iron protocol while another, with seemingly identical labs and symptoms, does not. The difference is in their biochemical individuality — the genetic and metabolic terrain that determines how their bodies process and utilize nutrients. Generic supplementation applied without this understanding is always going to produce inconsistent results.
What to Ask When Iron Isn’t Working
If you are taking iron and not improving, the most productive questions are not about the dose. They are about the context.
Is there underlying chronic inflammation, and if so, what is driving it? Is the gut environment healthy enough to absorb iron effectively? Are the methylation cofactors — B12 and folate in forms appropriate for this individual’s genetic picture — present and working? Is FUT2 secretor status affecting B12 absorption at the gut level? Are there cofactor deficiencies — copper, B6, riboflavin, vitamin C — that are preventing iron from being utilized? Is there an MTHFR variant affecting how B12 and folate are processed, and if so, which B vitamin forms are clinically appropriate? And is the form of iron being supplemented even right for this individual’s gut and absorption capacity?
Anemia is not a simple deficiency. It is a signal. What it is signaling — inflammation, gut dysfunction, methylation impairment, cofactor depletion, genetic variation — requires investigation, not just supplementation. When the root cause is found and addressed, iron levels often restore with far less supplementation and far faster timelines than the years of “keep taking the iron” that many women endure.
Brigitte Spurgeon works remotely with clients across the US, Canada, Europe, Asia, Africa, and Australia. She offers personalized nutrigenomics consultations and the Holistic Healing Strategy for root-cause healing. To learn more or inquire about working together, visit www.brigittespurgeon.com
This article is for educational purposes and does not constitute medical advice.
