9 Reasons Anemia Gets Complicated During the Perimenopause Transition
The number of women who spend a year assuming their bone-deep tiredness is just 'the menopause' — when they're actually running on dangerously low iron — is genuinely frustrating. A simple blood panel changes everything, but only if someone thinks to order the right one. Don't let fatigue get written off without bloodwork first.
Learn more about Rose →Perimenopausal periods can be dramatically heavier than anything before
In the years before periods stop, fluctuating estrogen and progesterone levels frequently produce anovulatory cycles — cycles without ovulation — which allow the uterine lining to build up thicker than normal before it sheds. The result can be flooding, clotting, and blood loss that far exceeds what the body can quietly replace between cycles. Iron-deficiency anemia caused purely by menstrual blood loss is clinically referred to as iron-deficiency anemia of chronic blood loss, and this is one of its most common drivers in midlife women.
Estrogen directly supports red blood cell production
Estrogen receptors are present on erythroid progenitor cells — the precursor cells in bone marrow that develop into red blood cells — and estrogen stimulates their proliferation. As estrogen levels decline and become erratic during perimenopause, this stimulatory effect weakens, which can subtly reduce red blood cell production even when iron stores are adequate. This means a woman can be dealing with both iron deficiency from bleeding and a quieter suppression of production at the same time.
Fatigue from anemia and fatigue from hormonal disruption feel almost identical
Both conditions produce the same surface-level exhaustion: low energy, difficulty concentrating, feeling washed out by midday. Because perimenopause fatigue is so commonly discussed, clinicians and women themselves often stop the diagnostic conversation there without checking a full blood count. The practical consequence is that treatable iron-deficiency anemia goes unidentified for months or even years while a woman is simply told this is a normal part of the transition.
Ferritin — not just hemoglobin — tells the real story
Hemoglobin can remain within the normal reference range even when iron stores are significantly depleted, a stage sometimes called iron depletion or pre-latent iron deficiency. Ferritin, the protein that stores iron, drops first and is a far more sensitive early marker. Many women in perimenopause have ferritin levels low enough to cause symptoms — particularly fatigue, hair shedding, and impaired cognitive function — while their hemoglobin still looks reassuringly normal on a standard blood panel.
Chronic low-level inflammation in midlife raises hepcidin and blocks iron absorption
Hepcidin is a liver hormone that acts as the body's iron gatekeeper — it blocks iron from moving from the gut into the bloodstream when it senses infection or inflammation. Midlife is associated with a gradual rise in background inflammatory signaling (sometimes called inflammaging), and this can elevate hepcidin enough to impair iron absorption even in women who are eating iron-rich diets. The result is a form of functional iron deficiency that responds poorly to standard oral supplementation alone.
Thyroid dysfunction — common in perimenopause — compounds the anemia picture
Hypothyroidism, which becomes more prevalent in women in their forties and fifties, independently causes anemia by slowing red blood cell production in the bone marrow. It also reduces gut motility in ways that can impair iron and B12 absorption. Since both thyroid dysfunction and perimenopause produce overlapping symptoms — fatigue, cold sensitivity, low mood, brain fog — the two conditions can mask each other, and anemia caused partly by thyroid disease can be attributed entirely to hormonal transition.
Vitamin B12 and folate deficiency can layer on top of iron deficiency
Iron-deficiency anemia and B12 or folate deficiency anemia can co-exist, and when they do, the classic laboratory markers become unreliable. B12 deficiency typically produces large red blood cells (macrocytosis), while iron deficiency produces small ones (microcytosis) — when both are present simultaneously, cell size can look deceptively normal on a standard count, masking both deficiencies. Women in perimenopause who eat less red meat, have reduced stomach acid, or have absorption issues are at higher risk of this combined picture.
Sleep disruption from night sweats accelerates iron depletion indirectly
Chronic sleep deprivation — the kind driven by vasomotor symptoms disrupting sleep multiple times a night — impairs the body's ability to regulate inflammatory cytokines, which in turn can elevate hepcidin and suppress erythropoiesis, the process of making red blood cells. There is also evidence that poor sleep independently worsens fatigue beyond what any single deficiency explains, making it harder to gauge how much of the exhaustion is attributable to anemia specifically. The two problems feed each other in ways that are difficult to untangle without testing.
Anemia worsens cognitive symptoms and mood in ways that look like perimenopause brain fog
Iron is essential for dopamine synthesis and for the myelin that insulates nerve pathways, which means even moderate iron deficiency impairs concentration, working memory, and emotional regulation — symptoms that closely mirror what many women describe as perimenopause brain fog or mood instability. When anemia is treated successfully, some women find that cognitive and mood symptoms improve significantly, suggesting that a portion of what was attributed to estrogen fluctuation was actually downstream of iron deficiency. This overlap is why anemia deserves to be ruled out as a contributor before hormonal changes take all the blame.
Want to go deeper?
Rose covers every symptom, supplement, and condition in full detail — evidence-graded and agenda-free.
Rose is a free, evidence-based reference built for women navigating perimenopause and menopause. No ads. No products to sell. No agenda. Just honest answers — because every woman in this season deserves a trusted friend who has done the research.