Women's health
The fatigue isn't hormonal: iron deficiency in perimenopause
Roughly one in three perimenopausal women presenting with fatigue have low iron stores. We test ferritin in the first consult, and it changes outcomes.
A patient in her late 40s describes “menopause fatigue” that came on over the last twelve months. She’s been told by friends, by Reddit, and by half the internet that it’s hormonal. Sometimes it is. Often, partly. But there’s a confounder almost everyone misses, including some GPs: she’s iron-deficient.
Across our first 50,000 menopause consults, we tested ferritin in every patient who reported fatigue. About one in three came back below the threshold where supplementation makes a meaningful difference. The conversation that follows changes outcomes more than most things we do in a hormonal-care plan.
Why iron deficiency rises in perimenopause
Two reasons:
- Cycle pattern changes. Perimenopausal bleeding is famously variable. Many women experience heavier flow, anovulatory bleeding, or shortened cycles. Even modest increases in monthly blood loss, sustained over years, deplete iron stores faster than most diets replenish them.
- Dietary intake is rarely keeping up. Even in patients with seemingly normal diets, the bioavailable iron requirement during this period is high. Plant-source iron is poorly absorbed without vitamin C cofactors. Coffee and tea, two of the most common everyday beverages, inhibit absorption when taken at meals.
The combination matters more than either factor alone.
Why it gets missed
A patient who says “I’m tired” to a GP in a 10-minute appointment, in her late 40s, very often gets an answer that orients around hormones. “It’s probably perimenopause.” Sometimes that ends the conversation. Sometimes MHT is started. Both are reasonable, but neither addresses iron status unless someone thought to check.
It’s a subtle attribution error: the most visible explanation (hormonal change) gets the credit for the symptom, and the less visible cause (iron depletion) goes untreated.
The ferritin debate
There’s genuine clinical disagreement on what threshold should trigger treatment. The traditional pathology-lab reference range starts at 30 ng/mL, but most contemporary literature and several Royal College guidelines now treat:
- <30 ng/mL as iron deficient
- 30–100 ng/mL with symptoms as iron-deficient-with-symptoms, treatment usually warranted
- >100 ng/mL as adequate stores
The 30–100 range is where the disagreement happens. In our experience, patients in this band who are still symptomatic improve with supplementation in 6–8 weeks. We err on the side of treating when the patient is symptomatic and other causes have been considered.
Treatment that actually works
Two things to get right:
- Oral iron, every other day, not daily. The evidence over the past decade has flipped: alternate-day dosing is better absorbed because it doesn’t trigger the hepcidin response that blocks subsequent doses. Daily oral iron actually produces worse outcomes per unit of elemental iron consumed.
- IV iron for patients who can’t tolerate oral, who don’t respond, or who are severely depleted. Modern IV iron is a single infusion in most cases, with low rates of side effects.
Either path, ferritin should be rechecked at 3 months. We’ve had patients on years of “menopause fatigue” treatment who responded to a single course of iron correction.
When to test
Our pathway: every patient who presents with fatigue, brain fog, or unexplained exercise intolerance gets full iron studies in the first consult. It’s a cheap test. It saves us from spending a year trying to optimise MHT for a patient whose real problem was iron.
The broader lesson: “hormonal fatigue” is a useful working hypothesis, not an answer. The answer comes from testing.
Related reading: why sleep isn’t the problem when perimenopausal women say they can’t sleep, and what 50,000 menopause consults taught us about getting the hormonal conversation right.