Why Iron Supplements Don't Always Work

You've been told your ferritin is low. You've started taking iron supplements. A few weeks in, you still feel exhausted, and your follow-up bloods haven't budged much. Sound familiar?

This is one of the most common frustrations I hear in clinic, and the answer almost always comes back to the same thing: inflammation.

Iron isn't just a nutrient you absorb passively. Your body has a highly sophisticated system for controlling exactly how much iron enters circulation, and when inflammation is present, that system slams the door shut. Understanding this changes everything about how we approach low iron.

Meet hepcidin: your body's iron gatekeeper

Hepcidin is a peptide hormone made by the liver, and it is the master regulator of iron in the body. Think of it as a traffic controller that decides how much iron gets to leave the gut and enter the bloodstream.

Here's how the system works. Iron absorbed from food travels into the cells lining your gut (enterocytes). To get out of those cells and into circulation, iron needs to cross via a protein called ferroportin, essentially a ferry boat shuttling iron across to a cargo ship called transferrin, which carries it to the bone marrow to make new red blood cells.

Hepcidin binds to ferroportin and sinks it. When ferroportin is blocked, iron is trapped inside the enterocyte. When those cells naturally shed (every few days), the iron goes with them. It was absorbed, but it never made it into your body.

This is a brilliantly clever protective mechanism. But it becomes a problem when hepcidin is chronically elevated.

What raises hepcidin?

Two main things: high iron stores (as in haemochromatosis) and inflammation. Specifically, the inflammatory signal IL-6 directly stimulates hepcidin production in the liver. And IL-6 is raised by insulin resistance, elevated cortisol, LPS (bacterial endotoxin from gut dysbiosis), chronic infection and autoimmune activity.

This is why we call it anaemia of chronic disease, or anaemia of inflammation. The iron is there, the body just cannot access it. Supplementing in this situation is often ineffective, and in some cases, unwise. Iron that can't enter circulation stays in the gut, where it can feed pathogenic bacteria. If someone has significant dysbiosis or a gut infection, flooding the intestines with extra iron can make things worse.

Hepcidin is also suppressed normally by low iron, hypoxia (low oxygen) and increased red blood cell production. This is why altitude training works: hypoxia suppresses hepcidin, allowing more iron to be absorbed and more red blood cells to be made. For those with sleep apnoea, the opposite effect can quietly impact iron metabolism over time.

When anaemia isn't really about iron at all

Not all anaemia is iron deficiency anaemia. Some people have conditions where red blood cells break down too quickly (haemolytic anaemia) or are made abnormally (such as in thalassaemia). In these situations, hepcidin is often inappropriately suppressed, meaning the body keeps absorbing iron even though it doesn't need more. Iron loading occurs despite anaemia. Supplementing iron here is actively harmful.

This is why working with a practitioner who looks at the full blood picture matters so much.

So what should you do if iron supplementation isn't working?

First, rule out inflammation as the driver. Look at transferrin saturation alongside ferritin. If ferritin is raised (or even normal) but transferrin saturation is low, iron is being stored but not moving, which strongly suggests an inflammatory process is blocking the system.

From there, the real work is addressing what's driving that inflammation. This might mean looking at gut health and LPS-producing bacteria, investigating insulin resistance, supporting adrenal health if cortisol is chronically elevated, or identifying and treating underlying infections or autoimmune activity.

Supporting stomach acid is often overlooked too. Adequate HCl keeps iron in its soluble, absorbable form at the brush border of the gut. If you're on acid-suppressing medication long-term, this is worth discussing with your practitioner.

Vitamin C alongside iron supplements or iron-rich meals genuinely helps by supporting that conversion from ferric to ferrous iron at the gut wall. And as I mentioned in the first post in this series, don't overlook copper. A copper-dependent enzyme is required at the point where iron exits the gut cell onto transferrin. Without adequate copper, iron can't get into circulation regardless of how much you're taking.

The practical summary

If you're not absorbing iron well, the supplement is rarely the problem. Start by asking whether inflammation could be the reason your system is locked down. A practitioner who understands the full iron pathway, not just haemoglobin, can help you get to the root of it rather than just topping up a leaking bucket.