Encyclopedia · supplement
Iron and ferritin
Low iron stores are common in people who shed hair, but no trial has shown that iron pills regrow hair, and nobody agrees on a hair-specific ferritin target.
What it is
Iron is a mineral needed for hemoglobin and for enzymes in fast-dividing cells, including hair-follicle matrix cells. Ferritin is the iron-storage protein, and serum ferritin is the standard test of body iron stores. Ferritin also rises with inflammation, infection and liver disease, which can hide a real deficiency; other tests such as transferrin saturation and CRP are then needed.
Iron deficiency is the world's most common nutritional deficiency. In premenopausal women it is usually from periods and pregnancy. In men and postmenopausal women it usually means blood loss or malabsorption, which needs a medical search. Trost 2006 Oral iron is sold without prescription in the US, EU and UK; intravenous iron is prescription-only.
How it works
In mice, iron deficiency starting before birth caused hair loss and abnormal follicles, reversed by restoring iron. Cell work pointed to reactive oxygen species suppressing Wnt/beta-catenin signalling in dermal papilla cells. This is animal and cell evidence only. Kwon 2026 In humans the idea that low iron pushes follicles into the resting phase is plausible but not proven by intervention trials.
What the studies show
The ferritin threshold debate:
- The WHO defines iron deficiency as ferritin under 15 micrograms/L in women. A CDC analysis of 7,498 US women proposed a physiology-based threshold of about 25 micrograms/L. Mei 2021
- Using under 25 micrograms/L, 38.6% of US females aged 12-21 were iron deficient; at 15 it was 17%; at 50 it was 77.5%. Weyand 2023
- A gastroenterology guideline uses under 45 ng/mL to diagnose iron deficiency in people with anemia. Without anemia the right threshold is uncertain. Ko 2020
- Women on a hormonal antiandrogen treatment (40 women) gained hair density only when ferritin was above 40 micrograms/L. It was not an iron trial. Rushton 1992
- One research group recommends ferritin around 70 micrograms/L for people with increased shedding while admitting the right level is not established. Rushton 2002
- A review found insufficient evidence to screen everyone with hair loss, or to give iron for hair in iron deficiency without anemia. Trost 2006
Is low ferritin linked to hair loss? The studies conflict.
- Supporting a link: 72% of 50 women with diffuse loss had ferritin below the lowest control value. Rushton 1990 Women with excessive hair loss were more likely to have iron stores under 40 micrograms/L (59% vs 48%, industry-authored, self-reported). Deloche 2007 Ferritin was lower in telogen effluvium (14.7) and female pattern loss (23.9) than controls (43.5 micrograms/L). Rasheed 2013 Odds of telogen hair loss were 21 times higher at ferritin 30 or below, with a very wide range of uncertainty. Moeinvaziri 2009
- Pooled data: a meta-analysis of 36 studies (10,029 people) found lower ferritin in women with non-scarring alopecia. Treister-Goltzman 2022 A 29-study meta-analysis found lower ferritin in telogen effluvium with high heterogeneity. Ahmed 2026 In 2,851 women with telogen effluvium, ferritin was low in 46.5% of those tested, though there was no control group. Karakoyun 2025
- Against a link: iron deficiency was common but not more common in female pattern loss or chronic telogen effluvium than in 76 controls (381 patients). Olsen 2010 In 181 women there was no correlation between ferritin above 10 micrograms/L and shedding rate. Bregy 2008 Among 194 women with biopsies, only 6.2% had ferritin of 20 or less, and the 5 with normal biopsies who took iron until ferritin passed 20 kept shedding. Sinclair 2002 In 90 women with chronic telogen effluvium, ferritin did not differ from controls. Durusu Turkoglu 2024
- Other groups: no ferritin difference in 764 people with alopecia areata across 10 studies Jin 2017, although in 33,401 people with alopecia areata iron-deficiency anemia was more common (15% vs 10%) Davidovici 2026. Men with pattern loss had normal ferritin (median about 222 vs 232 ng/mL). Debinta 2026
- Lower ferritin also went with hair loss after weight-loss surgery. Zhang 2021
Does giving iron regrow hair? We found no randomized trial with hair outcomes. Reviews from 2006 and 2010 note the same gap, and searches through October 2026 found none since. Rushton's group reported that some women with increased shedding responded to lysine plus iron; see L-lysine.
How it's used in studies
These are absorption trials, not hair trials. In iron-depleted women, single morning doses on alternate days were absorbed better than daily or split doses, because daily dosing raises hepcidin, which blocks absorption for about 24 hours. Stoffel 2017 In a double-blind trial of 150 women using 100 mg, alternate-day dosing gave the same ferritin at equal total dose with fewer gut side effects, and less iron deficiency at 6 months (3.0% vs 11.4%). von Siebenthal 2023 Dose, form and duration should come from the clinician who diagnosed the deficiency.
Side effects and safety
- Test first. Excess iron should be avoided, especially in hereditary hemochromatosis. Among people with two copies of the main HFE variant (C282Y), iron-overload disease developed in 28.4% of men and 1.2% of women over about 12 years. Allen 2008
- Iron pills are a leading cause of poisoning in young children. After US unit-dose packaging began, deaths in children under 6 fell from 29 to 1 over the compared periods. Tenenbein 2005 Keep them locked away.
- Nausea, constipation and abdominal discomfort are common and dose-related.
- Men and postmenopausal women with iron deficiency need a medical search for blood loss.
Bottom line
Ask for a ferritin test (with a blood count and CRP) if you shed diffusely and are in a risk group: heavy periods, vegetarian or vegan diets (ferritin about 30 micrograms/L lower than meat-eaters in a meta-analysis Haider 2018), frequent blood donation, or after weight-loss surgery. If ferritin is clearly low, treating the deficiency and its cause is standard care and hair may improve as a bonus; judge any hair response over months, since shedding follows a trigger by 3-4 months (see telogen effluvium). If ferritin is 30-70 micrograms/L, iron "for hair" is a judgment call with no trial support. For male pattern baldness, iron is not a treatment; see minoxidil and finasteride. Discuss with a doctor.
Studies 28
Trost LB et al. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. 2006
Result: Insufficient evidence to screen everyone with hair loss or to give iron for hair in iron deficiency without anemia.
Read the study ↗Rushton DH et al. Nutritional factors and hair loss. 2002
Result: Recommends ferritin around 70 micrograms/L for increased shedding, reports lysine plus iron responses, and warns that excess supplements can cause hair loss.
Read the study ↗Rushton DH et al. The importance of adequate serum ferritin levels during oral cyproterone acetate and ethinyl oestradiol treatment of diffuse androgen-dependent alopecia in women. 1992
Result: Hair density improved only when ferritin was above 40 micrograms/L; not an iron trial.
Read the study ↗Rushton DH et al. Biochemical and trichological characterization of diffuse alopecia in women. 1990
Result: 72% of women with blood tests had ferritin below the lowest control value.
Read the study ↗Sinclair R et al. There is no clear association between low serum ferritin and chronic diffuse telogen hair loss. 2002
Result: Only 6.2% had ferritin of 20 or less; the 5 with normal biopsies who took iron until ferritin passed 20 did not stop shedding.
Read the study ↗Kantor J et al. Decreased serum ferritin is associated with alopecia in women. 2003
Result: Mean ferritin lower in androgenetic alopecia (37.3) and alopecia areata (24.9) than controls (59.5 ng/mL); not lower in telogen effluvium; very small control group.
Read the study ↗Show 22 more studies
Deloche C et al. Low iron stores: a risk factor for excessive hair loss in non-menopausal women. 2007
Result: Low iron stores (under 40 micrograms/L) were more common in women reporting excessive hair loss (59% vs 48%); self-reported, industry-authored.
Read the study ↗Bregy A et al. No association between serum ferritin levels >10 microg/l and hair loss activity in women. 2008
Result: No correlation between ferritin above 10 micrograms/L and telogen rate; authors judged iron's role probably overestimated.
Read the study ↗Moeinvaziri M et al. Iron status in diffuse telogen hair loss among women. 2009
Result: Mean ferritin 16.3 vs 60.3 ng/mL; odds of telogen hair loss 21 times higher at ferritin 30 or below (wide interval).
Read the study ↗Olsen EA et al. Iron deficiency in female pattern hair loss, chronic telogen effluvium, and control groups. 2010
Result: Iron deficiency was common but not more common in patients than controls at 15 or 40 micrograms/L cut-offs.
Read the study ↗Rasheed H et al. Serum ferritin and vitamin d in female hair loss: do they play a role?. 2013
Result: Ferritin lower in telogen effluvium (14.7) and female pattern loss (23.9) than controls (43.5 micrograms/L).
Read the study ↗Treister-Goltzman Y et al. Iron Deficiency and Nonscarring Alopecia in Women: Systematic Review and Meta-Analysis. 2022
Result: Lower ferritin in women with alopecia (mean difference -18.5); about 21% had very low ferritin.
Read the study ↗Durusu Turkoglu IN et al. A comprehensive investigation of biochemical status in patients with telogen effluvium: Analysis of Hb, ferritin, vitamin B12, vitamin D, thyroid function tests, zinc, copper, biotin, and selenium levels. 2024
Result: Only zinc (lower) and selenium (higher) differed; ferritin, B12, vitamin D, biotin and hemoglobin did not.
Read the study ↗Karakoyun Ö et al. Retrospective Review of 2851 Female Patients With Telogen Effluvium: A Single-Center Experience. 2025
Result: Ferritin low in 46.5% of those tested; iron deficiency in 29.5%; no control group.
Read the study ↗Ahmed A et al. Association between Serum Trace Elements and Telogen Effluvium: A Systematic Review and Meta-Analysis. 2026
Result: Lower vitamin D (SMD -0.87) and lower ferritin (SMD -0.57) in telogen effluvium, with high heterogeneity.
Read the study ↗Jin W et al. Changes of serum trace elements level in patients with alopecia areata: A meta-analysis. 2017
Result: Lower zinc and selenium in alopecia areata; no difference in copper, iron, ferritin or magnesium.
Read the study ↗Davidovici B et al. The Association Between Alopecia Areata and Iron Deficiency Anemia: A Large-Scale Population-Based Case-Control Study. 2026
Result: Iron-deficiency anemia more common in alopecia areata (15% vs 10%; OR 1.61); it preceded alopecia areata in 40% of cases.
Read the study ↗Debinta AA et al. Serum ferritin and hair iron content in correlation to hair diameter and density: a case-control study. 2026
Result: No ferritin difference (median about 222 vs 232 ng/mL).
Read the study ↗Kwon SA et al. Iron Deficiency-Induced Hair Loss Is Associated with ROS-Mediated Disruption of Wnt/β-Catenin Signaling. 2026
Tested: iron deficiency and repletion
Result: Iron deficiency caused hair loss and abnormal follicles, reversed by iron, with ROS-mediated disruption of Wnt/beta-catenin signalling.
Read the study ↗Mei Z et al. Physiologically based serum ferritin thresholds for iron deficiency in children and non-pregnant women: a US National Health and Nutrition Examination Surveys (NHANES) serial cross-sectional study. 2021
Result: Physiology-based ferritin threshold for iron deficiency of about 25 micrograms/L.
Read the study ↗Weyand AC et al. Prevalence of Iron Deficiency and Iron-Deficiency Anemia in US Females Aged 12-21 Years, 2003-2020. 2023
Result: Iron deficiency in 38.6% at ferritin under 25, 17% under 15 and 77.5% under 50 micrograms/L.
Read the study ↗Ko CW et al. AGA Clinical Practice Guidelines on the Gastrointestinal Evaluation of Iron Deficiency Anemia. 2020
Result: In patients with anemia, a ferritin cut-off of 45 ng/mL diagnoses iron deficiency better than 15 (85% sensitivity, 92% specificity).
Read the study ↗Stoffel NU et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. 2017
Tested: iron 60 mg on consecutive vs alternate days
Result: Alternate-day single morning doses were better absorbed than daily or split dosing.
Read the study ↗von Siebenthal HK et al. Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study. 2023
Tested: iron 100 mg alternate-day vs consecutive-day
Result: Same ferritin at equal total dose, fewer gut side effects, and less iron deficiency at 6 months (3.0% vs 11.4%).
Read the study ↗Allen KJ et al. Iron-overload-related disease in HFE hereditary hemochromatosis. 2008
Result: Iron-overload disease developed in 28.4% of men and 1.2% of women.
Read the study ↗Tenenbein M et al. Unit-dose packaging of iron supplements and reduction of iron poisoning in young children. 2005
Result: After unit-dose packaging in 1997, iron poisoning deaths in children under 6 fell from 29 to 1 over the compared periods.
Read the study ↗Haider LM et al. The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis. 2018
Result: Ferritin averaged about 30 micrograms/L lower in vegetarians than meat-eaters, and about 62 micrograms/L lower in vegetarian men.
Read the study ↗Zhang W et al. Hair Loss After Metabolic and Bariatric Surgery: a Systematic Review and Meta-analysis. 2021
Result: Hair loss in 57%; lower folic acid (SMD -0.88), ferritin and borderline zinc associated with loss; B12 and iron were not.
Read the study ↗Related
- ZincTrue zinc deficiency causes hair loss that zinc fixes, but zinc has not been shown to regrow hair in people who are not deficient, and too much causes copper deficiency.
- Vitamin DHair loss goes with low vitamin D and the receptor is needed for the hair cycle, but no good trial shows supplements regrow hair if you are not deficient.
- Vitamin B12A real but uncommon cause of hair loss when deficient, with no evidence that extra B12 helps hair if your levels are normal.
- Folate (vitamin B9)A B vitamin that is sometimes low in people with hair loss, but not a hair-growth supplement if your levels are normal.
- L-lysineAn essential amino acid once paired with iron for women with shedding, with no recent independent trial.
- BiotinA B vitamin that restores hair only in the rare people who are deficient, and that can scramble thyroid and heart blood tests at the doses sold for hair.
- MinoxidilThe most widely used hair-growth treatment, available as a cheap over-the-counter lotion or foam and as a prescription tablet, with a mechanism that is still only partly understood.
- FinasterideA prescription pill (and in some countries a scalp spray) that lowers DHT and is the best-proven drug for stopping male pattern hair loss.
- Telogen effluviumA temporary burst of diffuse shedding that starts 2 to 3 months after a physical or emotional shock and usually settles within 6 months once the trigger is gone; it does not cause bald patches.
- Diet and hairCrash diets and rapid weight loss cause shedding, ordinary diets rarely do, and testing beats guessing before you buy supplements.