SLOT: Full Definition
What is iron / ferritin support?
Iron is the mineral that carries oxygen on hemoglobin and powers nearly every energy-producing reaction in the body. Ferritin is the storage form — your body's "iron savings account." Common supplemental forms include iron bisglycinate (well-tolerated), ferrous sulfate (potent but harder on the gut), heme iron polypeptide, and liquid liposomal iron.
Low iron is one of the most under-recognized drivers of thyroid symptoms in women. By the time hemoglobin drops and a woman is officially anemic, ferritin has often been low for months or years. At Modern Thyroid Clinic we routinely see women with ferritin in the teens or 20s being told their iron is "fine," while struggling with fatigue, hair shedding, and breathlessness.
Evidence in thyroid/hormone health
Iron is required at multiple steps in thyroid hormone production: it is part of the thyroid peroxidase enzyme that makes T4, and it supports T4 To T3 Conversion. Low ferritin is associated with Hypothyroidism, poor response to thyroid medication, and more pronounced Hair Loss. Women with Hashimotos Thyroiditis often have lower iron stores due to gut absorption issues and overlapping autoimmunity (such as celiac).
In hormone health, Heavy Periods Menorrhagia from fibroids, adenomyosis, or perimenopausal cycles is the leading cause of iron loss in women. Low iron also worsens [restless-legs-syndrome], Fatigue, Brain Fog, and exercise tolerance. Pregnancy, postpartum, and breastfeeding all increase iron needs.
Iron may help, can support, and is often used as a foundational nutrient — but it must be guided by labs. Both too little and too much iron cause harm, which is why self-supplementing is not recommended.
Who benefits most
Iron support is commonly considered for women with:
- Heavy or long menstrual periods
- Hair shedding, especially diffuse loss along the crown
- Fatigue and breathlessness on stairs
- Restless legs at night
- Hashimoto's with persistent symptoms despite optimized TSH
- Plant-based diets, postpartum, or pregnancy
A full iron panel — ferritin, serum iron, TIBC, and transferrin saturation — gives a much better picture than hemoglobin alone. Many functional clinicians aim for ferritin between 70 and 100 ng/mL to support hair growth and thyroid function in women.
What to look for in a product
Iron bisglycinate is gentle on the gut and well-absorbed. Ferrous sulfate raises iron faster but causes nausea and constipation in many women. Liquid and liposomal forms are options for those with sensitive stomachs. Take iron with vitamin C to boost absorption, and away from coffee, tea, calcium, and thyroid medication, which all reduce absorption.
Iron supplementation must complement, not replace, medical evaluation. Heavy bleeding, gut issues, and absorption problems all need to be addressed at the source. Your MTC clinician will interpret your iron panel and help build a plan that fits your symptoms, cycle, and thyroid care.
Common symptoms
Common questions
What ferritin level should I aim for as a woman with thyroid issues?
Standard labs flag deficiency below about 15 ng/mL, but most women feel well only when ferritin sits between 70 and 100 ng/mL — sometimes higher in those with hair loss or restless legs. Below 50, fatigue, hair shedding, and breathlessness are common, even with normal hemoglobin. At Modern Thyroid Clinic we set individual ferritin goals based on symptoms, menstrual blood loss, thyroid function, and overall health. Aiming for an optimal range, not just an above-deficiency number, often makes a clear difference in how women feel.
Why does my hair shed so much when iron is low?
Hair follicles are metabolically demanding and very sensitive to iron status. When ferritin drops, the body prioritizes vital functions and effectively redirects resources away from hair growth. The result is diffuse shedding, often noticed in the shower or on the pillow. Low iron compounds with thyroid issues, low vitamin D, and hormonal shifts to make hair loss worse. Restoring ferritin into an optimal range — alongside thyroid optimization — is one of the most reliable ways to slow shedding, though regrowth takes time.
Should I just buy iron over the counter?
We do not recommend it without testing. Both iron deficiency and iron overload (such as in hemochromatosis, which is more common than people think) can cause harm. Heavy menstrual bleeding, gut absorption issues, and celiac disease can all drive iron loss and need to be addressed at the source rather than masked. A full iron panel guides the right form, dose, and duration. Iron supplements can also interfere with thyroid medication absorption, so timing matters. A clinician should guide the plan.
Think you might be dealing with this?
Talk to a Modern Thyroid Clinic specialist about your symptoms, labs, and next steps.
Book a Discovery CallThis content is for educational purposes only and is not medical advice. Consult a licensed clinician for diagnosis and treatment. Content on this page does not create a doctor-patient relationship with Modern Thyroid Clinic.