Iron for Women: Heavy Periods, Ferritin Targets, and Thyroid Timing
Researched by DoseRoutine Research TeamReviewed for accuracy by Nicholas Alexander, RSE, SO, PMPLast updated Educational reference only — not medical advice. Always confirm dosing and safety decisions with a licensed clinician.
Summary
Iron deficiency without anemia (low ferritin, normal hemoglobin) is common in menstruating women and often overlooked. It causes fatigue, hair shedding, cold intolerance, and poor exercise recovery. The functional target is ferritin >30 ng/mL (many clinicians prefer >50–70 ng/mL, particularly for hair regrowth). Ferrous bisglycinate at 18–50 mg elemental iron/day is well tolerated; ferrous sulfate is cheaper but harder on the GI tract. Vitamin C improves absorption; calcium, coffee, tea, and thyroid medication reduce it. The biggest interaction to know is with levothyroxine — separate by 4 hours. Evidence level: strong for repletion of documented deficiency.
Key facts
| Studied dose range | 18–50 mg elemental iron/day if ferritin <30 ng/mL. Every-other-day dosing improves absorption vs daily. |
|---|---|
| Common forms | Ferrous bisglycinate (best tolerated), ferrous sulfate (cheap, more GI issues), heme iron (from meat, best absorbed) |
| Evidence level | Strong |
| Main interaction risks | Constipation. Overload in hemochromatosis. Chelates thyroid medication and antibiotics. |
What the research shows
Iron deficiency without anemia is common and under-diagnosed
Roughly 30-40% of menstruating women have iron deficiency without frank anemia (low ferritin, normal hemoglobin). CBC alone misses this. Fatigue, hair shedding, cold intolerance, restless legs, exercise intolerance, and cognitive fog are typical presentations. Camaschella (NEJM 2015) remains the standard clinical reference for the distinction between iron-deficient erythropoiesis and iron-deficiency anemia.
Alternate-day dosing (Stoffel 2017/2020)
Stoffel et al. (Lancet Haematol 2017, and follow-up 2020) showed that giving iron every other day, rather than daily or twice-daily, produces higher fractional absorption per dose and a comparable or better rise in hemoglobin over 4-8 weeks. Daily dosing raises hepcidin, which then blocks absorption of subsequent doses. Alternate-day dosing is now the emerging first-line pattern.
Ferrous bisglycinate tolerability
Milman et al. (Adv Ther 2019) and multiple manufacturer-independent trials show that ferrous bisglycinate produces significantly less nausea and constipation than equimolar ferrous sulfate, with equivalent hemoglobin response. The GI tolerability difference is the main reason to choose bisglycinate despite higher cost.
Hair loss and ferritin thresholds
Retrospective and small prospective work (Trost et al., J Am Acad Dermatol 2006; Rushton et al., Dermatology 2013) supports ferritin >70 ng/mL as a clinical threshold below which iron replacement may improve telogen effluvium and androgenetic hair thinning in women. The threshold is above the strictly hematologic cut-off because hair follicle iron demand exceeds erythropoietic demand.
Heavy menstrual bleeding is the driver
Heavy menstrual bleeding (HMB) is the single largest driver of iron deficiency in premenopausal women. Treating the bleeding pattern - LNG-IUD, tranexamic acid during menses, combined oral contraceptives, endometrial ablation - often produces larger long-term ferritin gains than iron supplementation alone. NICE HMB guidance (NG88) covers the treatment algorithm.
Levothyroxine chelation
Iron chelates levothyroxine in the gut, sharply reducing absorption. This is one of the most clinically important supplement-drug interactions in women. Standard practice: levothyroxine on empty stomach first thing in the morning, iron at lunch or evening, at least 4 hours apart. Failure to separate them frequently explains 'refractory' hypothyroidism in women who recently started iron.
IV iron for refractory cases
For women who cannot tolerate oral iron, have absorption issues (post-bariatric surgery, IBD, PPI use), or need rapid correction (pre-surgery, third trimester with severe anemia), single-dose IV iron formulations (ferric carboxymaltose, ferric derisomaltose) restore stores in one to two visits. Discuss with a hematologist or obstetrician.
Turn this evidence into a personal safety check for Iron (Cycle Context).
The interaction checker cross-references Iron (Cycle Context) against HRT, birth control, thyroid medication, SSRIs, and every other item in your stack — using the same clinical sources cited above.
Check Iron (Cycle Context) on the interaction checkerInteractions
Interaction risk is what makes women's-health supplements uniquely tricky — HRT, birth control, thyroid medication and SSRIs all share metabolic pathways with common botanicals. Each item below lists the mechanism and what to actually watch for.
- LevothyroxineMechanism: Iron chelates levothyroxine — reduces absorption sharply.Watch for: Separate by 4 hours. Standard practice: levothyroxine first thing on empty stomach, iron at lunch or evening.Check Iron (Cycle Context) + Levothyroxine on the interaction checker
- Calcium supplements and dairyMechanism: Compete for absorption.Watch for: Separate by 2 hours.Check Iron (Cycle Context) + Calcium supplements and dairy on the interaction checker
- Coffee, tea, red wine (polyphenols)Mechanism: Bind iron in gut.Watch for: Separate by 1–2 hours.Check Iron (Cycle Context) + Coffee, tea, red wine (polyphenols) on the interaction checker
- Vitamin CMechanism: Improves non-heme iron absorption.Watch for: Take iron with vitamin C or citrus.Check Iron (Cycle Context) + Vitamin C on the interaction checker
- Antibiotics (tetracycline, quinolones)Mechanism: Chelation.Watch for: Separate by 2–4 hours.Check Iron (Cycle Context) + Antibiotics (tetracycline, quinolones) on the interaction checker
- Proton pump inhibitors and antacidsMechanism: Reduce iron absorption via reduced stomach acid.Watch for: Discuss with prescriber; may need higher iron dose.Check Iron (Cycle Context) + Proton pump inhibitors and antacids on the interaction checker
- HRT and birth controlMechanism: COCs typically reduce menstrual bleeding, improving iron status.Watch for: Iron needs may drop after starting COCs.Check Iron (Cycle Context) + HRT and birth control on the interaction checker
Who should be cautious
- Hereditary hemochromatosis — do not supplement without screening.
- Ferritin >100 ng/mL — supplementation is rarely needed.
- GI upset — try ferrous bisglycinate, take with food (accept slight absorption loss), or every-other-day dosing.
- Kids in the house — iron overdose is one of the most common accidental poisonings; store securely.
FAQ
What ferritin level should I target?
Most labs flag <15 ng/mL as deficient, but many clinicians target >30 ng/mL functional minimum, and >50–70 ng/mL for hair growth, energy, or endurance training. Above 100 ng/mL is rarely needed and can be a sign of inflammation.
How do I take iron with levothyroxine?
Separate by at least 4 hours. Standard timing: levothyroxine 6am on empty stomach, iron with lunch or evening meal + vitamin C. Do not stack them within the same hour.
Ferrous bisglycinate vs ferrous sulfate?
Bisglycinate is better tolerated (less constipation and nausea) at comparable elemental iron doses. Sulfate is cheaper. For anyone struggling with side effects, bisglycinate is worth the small price premium.
Do I need iron if I have heavy periods?
Very likely — heavy menstrual bleeding is the leading cause of iron deficiency in menstruating women. Get a ferritin level and treat both the deficiency and the underlying bleeding pattern (COCs, LNG-IUD, tranexamic acid can help).
Can I take iron with a prenatal vitamin?
Most prenatals contain 18–27 mg iron. If your ferritin is <30 ng/mL in early pregnancy, additional iron on top of prenatal is often needed. Discuss with your obstetrician.
Where can I check iron interactions with my other supplements?
Use the DoseRoutine interaction checker at doseroutine.com/interaction-checker to add every fertility supplement plus your prenatal, thyroid medication, or fertility prescription in one view.
Taking Iron (Cycle Context) alongside HRT, birth control, or other supplements?
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Sign up freeSources
- Stoffel NU et al. Lancet Haematol 2017 - Alternate-day iron dosing.
- Stoffel NU et al. Haematologica 2020 - Alternate-day iron in iron-depleted women follow-up.
- Camaschella C. NEJM 2015 - Iron-deficiency anemia clinical review.
- Milman N et al. Adv Ther 2019 - Ferrous bisglycinate tolerability review.
- Rushton DH et al. Dermatology 2013 - Iron status and female hair loss.
- NICE NG88 - Heavy menstrual bleeding: assessment and management.
- NIH Office of Dietary Supplements - Iron professional fact sheet.
Source: DoseRoutine Library — doseroutine.com/library/womens-health/iron-cycle