How much iron do women lose during menstruation?

By Sina Hartung, MMSC-BMI, Harvard Medical SchoolReviewed by Eureka Health Medical Group
Published: July 4, 2025Updated: July 4, 2025

Summary

Most women lose 15–30 mg of iron during an average 4–5-day period, because each millilitre of blood contains about 0.5 mg of iron and the typical cycle sheds 30–60 mL of blood. Losses jump above 40 mg when bleeding exceeds 80 mL, which is the clinical cut-off for heavy menstrual bleeding (HMB) that can trigger iron-deficiency anaemia.

How many milligrams of iron does menstruation remove in most women?

A standard menstrual cycle sheds 30–60 mL of blood. Because 1 mL of blood carries roughly 0.5 mg of iron, that translates to 15–30 mg lost per month. “Put simply, the iron you lose in one period is about the amount contained in a small iron tablet,” explains Sina Hartung, MMSC-BMI.

  • Average iron loss is 15–30 mg per cycle30–60 mL x 0.5 mg Fe/mL = 15–30 mg iron, equivalent to 10–20 % of the recommended daily allowance (RDA) for pre-menopausal women.
  • Heavy bleeding crosses the 40 mg thresholdBleeding above 80 mL per cycle removes 40 mg or more of iron and is clinically labelled heavy menstrual bleeding (HMB).
  • Annual iron loss adds up quicklyOver 12 cycles, even normal flow can drain 180–360 mg—almost two months’ worth of dietary iron.
  • Menstruation adds about 1 mg of iron loss each dayThe AMA points out that the roughly 30 mg lost per month during periods equates to about 1 mg daily—doubling the baseline 1 mg lost through normal skin and gut shedding. (AMA)
  • Individual losses can range widely between 11 and 23 mgA metabolic study of four healthy women recorded menstrual iron losses from 11.1 mg to 22.8 mg per cycle, highlighting significant person-to-person variability. (SciDirect)

References

How can I tell if my period-related iron loss is too high?

Identifying heavy menstrual bleeding early protects you from iron-deficiency anaemia. The team at Eureka Health warns that needing to change a fully soaked pad or tampon more often than every two hours is a red flag.

  • Passing clots larger than a quarterClots bigger than 2.5 cm often signal flow above 80 mL.
  • Soaking through bedding or clothingNight-time leakage suggests blood loss high enough to outstrip the absorbent capacity of standard products.
  • Fatigue within the first two days of bleedingEarly-cycle exhaustion may indicate rapid iron depletion rather than normal hormonal tiredness.
  • Pica or craving iceStudies show that 15–20 % of women with HMB report non-food cravings, a classic sign of iron deficiency.
  • Bleeding that lasts more than 7 days usually exceeds the 80 mL heavy-flow cutoffPeriods persisting a week or longer fit the clinical definition of heavy menstrual bleeding and should prompt iron checks. (VWH)
  • Losing a cup of menstrual blood can strip 200–250 mg of ironSuch high volume loss puts you at high risk for iron-deficiency anemia unless intake is boosted. (IronDisorders)

References

Which factors can increase iron loss during periods?

Several medical and lifestyle issues magnify menstrual blood volume. “Uterine fibroids are the single most common anatomical reason we see for excessive iron loss,” notes Sina Hartung, MMSC-BMI.

  • Uterine fibroids raise flow by up to 70 %Large intramural or submucosal fibroids enlarge uterine surface area, boosting bleeding duration and volume.
  • Copper IUDs add 10–20 mL of blood per cycleNon-hormonal IUDs can trigger heavier, longer periods, especially in the first six months.
  • Bleeding disorders like vWDAbout 13 % of adolescents with heavy periods have an undiagnosed bleeding tendency such as von Willebrand disease (vWD).
  • Low dietary iron before the cycle startsEntering menstruation with borderline ferritin (<30 ng/mL) means each milligram lost has a bigger physiological impact.
  • Heavy flow above 80 mL can more than double iron lossA Filipino cohort found a median 37 mL of menstrual blood per cycle, but women exceeding the 80 mL menorrhagia threshold lost up to 169 mL—equating to roughly 0.55 mg of iron every day throughout the cycle. (PubMed)
  • Two-thirds of women experience heavy bleeding at least onceSurvey data indicate 67 % of women report an episode of heavy menstrual bleeding, and 51 % say it occurs in most cycles, underscoring how common iron-depleting periods are. (ActiveIron)

References

What daily habits can limit iron deficiency from menstruation?

Small, consistent changes help most women replace monthly losses without prescription therapy. The team at Eureka Health adds that spacing iron-rich meals away from coffee or tea increases absorption by up to 50 %.

  • Pair iron sources with vitamin CAdding bell peppers or citrus boosts non-heme iron uptake two-fold.
  • Cook in cast-iron cookwareStudies show an extra 1–2 mg of iron per serving when acidic foods are prepared in cast iron.
  • Avoid calcium supplements within two hours of ironCalcium competes for the same transporters and can cut absorption by one-third.
  • Track period volume in an appRecording pad or tampon counts helps recognise creeping increases that warrant medical review.
  • A typical period drains roughly 30–45 mg of ironHealth.com estimates that losing 2–3 tablespoons of blood per cycle translates to 30–45 mg of iron, underscoring the need for steady dietary replacement. (Health)
  • Menstruating adults should target at least 18 mg of iron dailyGutHealthDietitian states the RDA climbs to 18 mg for women aged 19–50, with heavier flows potentially demanding even higher intakes. (GHD)

References

Which blood tests and treatments address menstrual iron loss?

Lab work pinpoints whether heavy periods are causing deficiency. “Ferritin below 30 ng/mL plus a transferrin saturation under 20 % confirms depleted iron stores,” says Sina Hartung, MMSC-BMI.

  • Serum ferritin is the first-line markerA level under 15 ng/mL is diagnostic of iron-deficiency anaemia (IDA); 15–30 ng/mL is borderline.
  • Complete blood count reveals chronic lossMicrocytic, hypochromic red cells and an MCV below 80 fL suggest longstanding IDA.
  • Oral iron therapy replenishes 100–200 mg weeklyTypical elemental iron dosing (40–65 mg once daily) doubles iron intake compared with diet alone.
  • IV iron reserved for intolerance or severe IDAFerric carboxymaltose can deliver 1 g in a single infusion when oral therapy fails.
  • Heavy bleeding (>80 mL) causes iron deficiency in 80 % of womenMenorrhagia is officially defined as more than 80 mL per period, and 80 % of patients meeting this threshold show laboratory evidence of iron deficiency. (CEMCOR)
  • Up to 60 % of heavy-period patients are severely iron-deficientAmong women evaluated for heavy menstrual bleeding, 27 % were anemic and 60 % had severely depleted ferritin; iron supplementation restored hemoglobin and improved quality-of-life scores. (ScienceDaily)

References

How can Eureka’s AI doctor guide you through heavy periods?

Eureka’s AI doctor reviews your symptom log, estimates blood loss from your pad counts, and flags when you breach the 80 mL threshold. The team at Eureka Health emphasises that the system uses the same clinical criteria gynaecologists rely on.

  • Automated ferritin test suggestionsIf your answers point to possible IDA, the app can request a ferritin and CBC panel for physician review.
  • Medication triageWhen heavy bleeding persists, the AI lists evidence-based options (e.g., tranexamic acid, hormonal IUD) and routes the request to a human clinician.
  • 4.8-star user satisfaction among women tracking period ironIn-app surveys show high confidence in the personalised alerts and dietary guidance.

Why women use Eureka’s AI doctor for iron levels and periods

Privacy, speed, and continuous follow-up make digital care attractive. “Many of my patients feel heard for the first time when they chat with the AI before their appointment,” notes Sina Hartung, MMSC-BMI.

  • 24/7 access without waiting roomsLog symptoms the moment they occur and get immediate feedback.
  • Data-driven treatment plansLongitudinal charts of ferritin, cycle length, and flow help clinicians adjust therapy precisely.
  • Safe review by licensed doctorsEvery prescription or lab order suggested by the AI is vetted by Eureka’s medical team for safety and relevance.

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Frequently Asked Questions

Does the 15–30 mg of iron lost during a period need to be replaced immediately?

Ideally, yes. Meeting the daily RDA (18 mg) and eating iron-rich foods during and after your period usually covers the loss in 1–2 weeks.

I follow a plant-based diet; is my menstrual iron loss riskier?

Non-heme iron from plants is absorbed at only 5-10 %, so vegetarians should aim for about 1.8 times the RDA to offset lower absorption.

Can hormonal birth control reduce iron loss?

Yes. Combined oral contraceptives and hormonal IUDs can cut menstrual blood volume by 40–90 %, lowering monthly iron loss accordingly.

Is taking an over-the-counter iron supplement safe during my period?

Most women tolerate 18–27 mg elemental iron daily, but stomach upset is common. Check with a clinician before starting any supplement.

How accurate is using pad or tampon counts to estimate blood loss?

Counting soaked products provides a rough estimate but tends to over- or under-report by 20 %. Period tracking cups with measurement lines are more precise.

Can I donate blood if I have heavy menstrual bleeding?

Blood centres often defer donors with low haemoglobin or ferritin. Get your levels checked first to avoid worsening iron deficiency.

Will pregnancy erase iron deficiency caused by heavy periods?

No. Pregnancy increases iron needs to roughly 1 g total. Pre-existing deficiency can worsen without supplementation.

This content is for informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare provider for diagnosis, treatment, and personalized medical recommendations.

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