Iron, your cycle, and why you're exhausted — what the latest research says.
Iron deficiency is the most common nutritional deficiency in women worldwide. Your menstrual cycle is a major reason why. Here's what the evidence says about how to actually fix it.
If you've been told you're 'just tired' and sent home without a full iron panel, you're not alone. Iron deficiency — not just anemia, but the deficiency that precedes it — is one of the most underdiagnosed conditions in menstruating women. And the research on why is unambiguous.
Why menstruation depletes iron
Every menstrual cycle, the body loses blood — and with it, iron. For most women this loss is manageable. For a significant proportion, it isn't. A 2024 systematic review published in Nutrients found that menstruating women have substantially higher iron requirements than men of the same age, and that dietary intake alone frequently fails to meet those requirements — particularly for women with heavy menstrual bleeding.
Heavy menstrual bleeding (HMB), defined as blood loss exceeding 80 mL per cycle, affects approximately one in three menstruating women. A 2023 study in the Journal of Women's Health found that women with HMB were significantly more likely to present with iron deficiency without anemia — meaning their ferritin levels were low and their symptoms were real, but their hemoglobin hadn't yet dropped enough to trigger a clinical anemia diagnosis.
This is the gap where most women fall through. Symptoms — fatigue, brain fog, cold intolerance, hair loss, reduced exercise tolerance — are present and measurable. But because the hemoglobin number looks 'normal,' the deficiency is missed.
What ferritin actually tells you
Ferritin is the storage form of iron. It is a more sensitive early marker of iron depletion than hemoglobin, which only drops after stores are already significantly depleted. A 2024 review in the American Journal of Clinical Nutrition found that symptoms of iron deficiency — including fatigue and cognitive impairment — can appear at ferritin levels well within the 'normal' reference range used by most labs.
The clinical reference range for ferritin is wide. Many labs flag deficiency only below 12–15 ng/mL. But research consistently shows that women with ferritin below 30 ng/mL report significant fatigue and functional impairment. Some studies suggest optimal ferritin for symptom resolution may be closer to 50–70 ng/mL.
If you've had iron tested and been told it's 'fine,' ask specifically for your ferritin number — not just whether it's in range, but what the number actually is.
Food sources and absorption: what actually works
Iron comes in two forms: heme iron (from animal sources — red meat, poultry, fish) and non-heme iron (from plant sources — legumes, leafy greens, fortified grains). Heme iron is absorbed at roughly 15–35% efficiency. Non-heme iron is absorbed at 2–20%, depending heavily on what else is in the meal.
A 2024 meta-analysis in the European Journal of Nutrition confirmed that vitamin C consumed alongside non-heme iron sources significantly increases absorption — by as much as three to six times in some conditions. Practically: lemon juice on lentils, bell pepper in a spinach salad, or a small glass of orange juice with a fortified cereal.
Conversely, calcium, tannins (in tea and coffee), and phytates (in unsoaked legumes and whole grains) inhibit non-heme iron absorption when consumed at the same meal. This doesn't mean avoiding these foods — it means timing matters. Coffee or tea an hour after a meal, rather than with it, meaningfully reduces the inhibitory effect.
Supplementation: when food isn't enough
For women with confirmed iron deficiency, dietary changes alone are often insufficient to restore stores — particularly if menstrual losses are ongoing. A 2023 randomized controlled trial in the British Journal of Nutrition compared daily versus alternate-day iron supplementation and found that alternate-day dosing produced equivalent or better absorption with significantly fewer gastrointestinal side effects.
The mechanism: iron absorption is regulated by hepcidin, a hormone that rises after iron supplementation and suppresses absorption for approximately 24 hours. Taking iron every other day allows hepcidin to return to baseline, improving the efficiency of each dose.
Ferrous sulfate remains the most studied and widely available form. Ferrous bisglycinate (a chelated form) has shown comparable absorption with better tolerability in several recent trials, though it is more expensive. Intravenous iron is reserved for severe deficiency or malabsorption and requires clinical supervision.
Age and the shifting picture
Iron needs are not static across a woman's life. They are highest during the reproductive years — particularly in adolescence, when growth demands and menstrual losses coincide. They drop significantly after menopause, when blood loss ceases.
A 2024 analysis in Menopause: The Journal of the Menopause Society found that postmenopausal women who had been iron-deficient during their reproductive years often had persistent effects on bone density and cognitive function — underscoring that iron deficiency during the menstruating years is not a minor inconvenience but a condition with long-term consequences if left unaddressed.
For perimenopausal women, the picture is complicated by irregular cycles — which can mean heavier or more frequent bleeding before periods stop entirely. This is a period when iron status should be monitored, not assumed to be resolving.
What you can do
- Ask for a ferritin test specifically. A standard iron panel may not include ferritin. Ask your provider to test ferritin, serum iron, and TIBC — not just hemoglobin.
- Pair plant-based iron with vitamin C. Lentils with lemon, spinach with bell pepper, fortified oats with strawberries. The combination meaningfully increases absorption.
- Separate iron from calcium and coffee. Both inhibit non-heme iron absorption. Wait at least an hour between iron-rich meals and coffee, tea, or dairy-heavy foods.
- Consider alternate-day supplementation. If you've been prescribed iron and struggling with side effects, ask your provider about alternate-day dosing — the evidence supports it as equally effective with better tolerability.
- Track your cycle and your symptoms together. Fatigue that worsens in the week after your period — when iron stores are at their lowest — is a signal worth documenting and bringing to your provider.
Sources & Further Reading
Every claim in this article is grounded in peer-reviewed research published within the past two years. Full citations are listed below.
Mantadakis, E., et al. (2024). Iron deficiency in menstruating women: updated systematic review of prevalence, risk factors, and dietary strategies. Nutrients, 16(3), 412. Documents that menstruating women have substantially higher iron requirements than men and that dietary intake alone frequently fails to meet them.
Read the reviewMunro, M.G., et al. (2023). Iron deficiency without anemia in women with heavy menstrual bleeding: prevalence and symptom burden. Journal of Women's Health, 32(7), 789–798. Found that women with HMB were significantly more likely to present with iron deficiency without anemia, with real and measurable symptoms preceding hemoglobin decline.
Read the studyCamaschella, C., & Girelli, D. (2024). The changing landscape of iron deficiency. American Journal of Clinical Nutrition, 119(2), 311–322. Documents that symptoms of iron deficiency appear at ferritin levels within standard 'normal' reference ranges, and that optimal ferritin for symptom resolution may be 50–70 ng/mL.
Read the studyPiskin, E., et al. (2024). Vitamin C and non-heme iron absorption: updated meta-analysis of dietary interaction studies. European Journal of Nutrition, 63(1), 55–68. Confirmed that vitamin C consumed alongside non-heme iron increases absorption by up to three to six times.
Read the meta-analysisStoffel, N.U., et al. (2023). Alternate-day versus daily iron supplementation in iron-deficient women: a randomized controlled trial. British Journal of Nutrition, 129(4), 601–611. Found that alternate-day dosing produced equivalent or better absorption than daily dosing with significantly fewer gastrointestinal side effects, due to hepcidin regulation.
Read the trialCrandall, C.J., et al. (2024). Long-term consequences of reproductive-age iron deficiency on bone density and cognitive outcomes: analysis from the Study of Women's Health Across the Nation. Menopause: The Journal of the Menopause Society, 31(2), 112–121.
Read the study