Why Is My Ferritin Low? The Real Causes of Iron Deficiency in Perimenopause

What Does Ferritin Actually Measure, and Why Do "Normal" Labs Miss It?

Ferritin is your body's iron savings account. Hemoglobin is the cash in your wallet. You can have a full wallet and an empty savings account at the same time. That's exactly what happens to most perimenopausal women with iron deficiency: hemoglobin still reads normal, so a standard complete blood count comes back clean, while ferritin has quietly dropped to the floor. This is called non-anemic iron deficiency. It produces every classic symptom of low iron long before anemia shows up.

The reference range makes it worse. Most labs flag ferritin as low only under 15 ng/mL. But the symptom data tells a different story, and the thresholds vary by what you're trying to fix.

A woman with a ferritin of 22 is told she is fine when she is functionally deficient by every measure that matters. Normal is not the same as optimal.

Why Can Ferritin Look Normal When I'm Still Iron Deficient?

Here's the catch that traps even careful clinicians. Ferritin is an acute-phase reactant. It rises with inflammation independent of how much iron you actually have stored. An inflamed body can show a falsely reassuring ferritin. A woman with active gut inflammation or an unaddressed infection can be genuinely iron-deficient and still post a ferritin of 60 or 80.

This is why ferritin should never be read alone. Interpret it alongside hs-CRP, a marker of inflammation. If CRP is elevated, a "normal" ferritin may be hiding a real deficiency underneath it.

Iron deficiency is rarely just an iron problem. It's almost always a downstream symptom of something else.

What Actually Causes Low Ferritin in Perimenopause?

Iron only leaves the body three ways: you lose it, you fail to absorb it, or you can't use it. Perimenopause pushes on all three at once.

Heavy and erratic menstrual bleeding is the number-one cause. As progesterone falls and cycles become anovulatory, estrogen goes unopposed and builds a thicker uterine lining. It sheds as heavier, longer, flooding periods. Fibroids, common in the 40s, add to the loss. Heavy menstrual bleeding is clinically defined as more than 80 mL of blood loss per cycle,¹ and a woman losing that much cannot out-eat it with diet alone. Iron deficiency often gets worse in perimenopause before it resolves at menopause. The bleeding gets heavier before it stops.

You can't absorb the iron you're eating. Iron needs an acidic stomach to become absorbable. Stomach acid declines with age, drops under chronic stress, and is suppressed outright by the acid-blocking medications so many women take for perimenopausal reflux. Iron is absorbed in the duodenum, and celiac disease, IBD, SIBO, and intestinal permeability all damage exactly that surface. Estrogen helps maintain the tight junctions of the gut lining, so an erratic estrogen supply makes the barrier more permeable and inflamed right when demand is highest. H. pylori does double damage: it lowers stomach acid and slowly bleeds the stomach lining.

Hepcidin is the master switch that locks iron away. This is the mechanism most women are never told about. Hepcidin is a liver hormone that controls iron traffic. When the body senses inflammation, it releases IL-6, which drives hepcidin up. High hepcidin blocks iron absorption in the gut and locks stored iron inside your cells so it can't be used. You can swallow iron every day and absorb almost none of it, because inflammation closed the gate. You cannot supplement past high hepcidin. You have to lower the inflammation driving it.

The cofactors iron can't work without. Copper builds the protein that mobilizes iron out of storage. Vitamin C reduces iron into its absorbable form. Vitamin A releases stored iron, and B vitamins build red blood cells. A shortfall in any of them creates a functional iron deficiency even when intake is fine.

Hidden loss and hidden demand. The ibuprofen women reach for to manage heavy periods and joint pain causes low-grade stomach bleeding. Occult GI bleeding from an ulcer or polyp is silent, so iron deficiency in a woman who isn't bleeding heavily always deserves a GI workup. Hypothyroidism slows stomach acid and red-cell production, and iron and thyroid drag each other down bidirectionally. Hard endurance training raises hepcidin and destroys red cells through foot-strike.

If ADHD is part of your picture too, iron deficiency and ADHD severity track together through this same dopamine pathway; see Iron, Ferritin, and ADHD for the trial data and why you should test before you supplement.

Why Does Low Iron Affect So Much More Than Just Energy?

Iron is not only about anemia. It runs the machinery of everything perimenopause is already straining. Iron builds ATP in your mitochondria, which is why deficiency reads as bone-deep fatigue. It's a cofactor for the enzymes that make dopamine and serotonin, which is why low iron shows up as brain fog, low mood, and restless legs. It's essential for thyroid conversion, hair follicle cycling, and the oxygen delivery that decides whether exercise builds you up or wipes you out.

In a life stage defined by protecting muscle, brain, and bone for the decades ahead, chronically low iron quietly undermines all of it. And it's routinely left on the table because the standard blood count looked fine.

What Labs Should I Actually Ask For?

Ask for a full picture, not a hemoglobin and a shrug.

Ferritin, read against inflammation, is the single most important number. Add hs-CRP so you can tell whether ferritin is real or propped up. Serum iron, TIBC, and transferrin saturation round out the iron panel; a saturation under 20 percent points to true deficiency. A complete blood count catches anemia once it develops. B12 and folate travel with iron and are worth checking together. A thyroid panel covers the bidirectional partner. Depending on your picture, consider a celiac screen, H. pylori testing, and a stool test if absorption or hidden bleeding is suspected.

For the full rationale on which labs matter and why sex hormones aren't on this list, see What Are the Best Labs to Test During Perimenopause?

How Do I Actually Fix Low Ferritin? (The Order That Works)

Repletion fails when it skips straight to the pill.

First, stop the loss. If bleeding is heavy, that's the first conversation: progesterone support where appropriate, evaluating fibroids, reviewing NSAID use. You cannot fill a bucket that is still draining.

Second, open the absorption gate. Lower the inflammation driving hepcidin, support stomach acid, and address gut issues or H. pylori.

Third, supplement smartly. A single dose taken every other day is absorbed better than daily dosing, because a large daily dose spikes hepcidin and blunts absorption the next day.² Take iron with vitamin C, away from coffee, tea, and calcium. Choose a gentle form like bisglycinate, and pair it with the cofactors copper, vitamin A, and riboflavin.

Fourth, eat for iron. Red meat, liver, and shellfish deliver the most absorbable heme iron.

Fifth, retest at 8 to 12 weeks. Keep going until you clear a functional target of 50 to 100 ng/mL, not just until you exit the red zone at 15.

References

1. StatPearls/NCBI, "Abnormal Uterine Bleeding" — heavy menstrual bleeding defined as >80 mL of blood loss per cycle.
2. Stoffel et al., The Lancet Haematology, 2017 — alternate-day iron dosing improves fractional absorption and produces lower hepcidin than daily dosing.

The ferritin-threshold table above carries its own sourcing in the Source column (Vaucher et al., CMAJ, 2012; IRLSSG treatment guideline, 2018; clinical/dermatology consensus for hair regrowth) and was left as-is in this pass.