Low Ferritin Symptoms: What a Normal Blood Count Can Miss in Women With Thyroid Problems

She was 41 and had been on thyroid medication for six years. Her TSH was right where her doctor wanted it. She was still exhausted by 2 p.m., her hair was collecting in the shower drain, and her heart raced every time she climbed the stairs.

Her blood count came back normal, so she was told she wasn’t anemic and her iron was fine.

Nobody had checked her ferritin. When someone finally did, it was 11 ng/mL.

Sound familiar? This pattern shows up constantly in women with Hashimoto’s low thyroid. The reason it gets missed is simple: the standard blood count checks for anemia, and you can run out of stored iron long before you become anemic.

What Ferritin Actually Measures

Ferritin is the protein that stores iron. Think of hemoglobin as your checking account and ferritin as your savings. Your body will drain savings for a long time to keep checking looking normal.

That’s why a normal hemoglobin doesn’t rule out iron deficiency. Anemia is the late stage. Your reserves can be depleted well before it shows up, and low iron can cause symptoms on its own, even without anemia.

This isn’t rare. A 2023 study in JAMA found that 38.6% of US girls and young women ages 12 to 21 had iron deficiency, defined as ferritin below 25 ng/mL. Only 6.3% had iron-deficiency anemia. That study didn’t look at older women or at Hashimoto’s specifically, but it shows how much a hemoglobin check alone can miss.

What Counts as Low Ferritin

Here’s where it gets confusing, because “low” depends on who you ask.

A ferritin below 15 ng/mL means your iron stores are essentially empty. Below 30 generally points to low stores. The American Gastroenterological Association uses a cutoff of 45 ng/mL when evaluating patients who already have anemia.

Yet many lab reports won’t flag anything until ferritin drops into the low teens or below. So a ferritin of 18 can look “in range” on paper while sitting in territory most iron guidelines would call low.

Many functional medicine practitioners, myself included, prefer to see ferritin well above those minimums in women with thyroid symptoms or hair loss. That is a clinical preference, not an established guideline, and it’s one reason your results need to be interpreted alongside your symptoms and history rather than against a single number.

Why Normal Ferritin Isn’t Always Reassuring

Ferritin rises with inflammation, infection, and liver disease. That means it can read higher than your true iron stores.

The World Health Organization recognizes this. In people with infection or inflammation, WHO considers a ferritin below 70 µg/L (the same as ng/mL) consistent with iron deficiency in adults. If you have an active autoimmune flare, leaky gut, or fatty liver, a “normal” ferritin may not be telling the whole story. Transferrin saturation and C-reactive protein help clarify it.

The Iron and Thyroid Connection

Your thyroid builds hormone using an enzyme called thyroid peroxidase (TPO), and TPO requires iron. When iron runs low, that step has less of what it needs.

Converting T4 into T3, the active hormone your cells use, depends mainly on selenium-containing enzymes. Animal research suggests iron deficiency can also impair thyroid hormone metabolism, but that hasn’t been proven to routinely block thyroid medication in people.

What research does show is that iron deficiency and poor thyroid function tend to travel together. Part of the reason is that the relationship runs both directions. Hypothyroidism is associated with heavier periods, which means more iron lost every month. Hashimoto’s also overlaps with celiac disease and autoimmune gastritis, and both interfere with iron absorption.

And even when thyroid treatment is adequate, iron deficiency can make you feel unwell on its own. If your thyroid is “well managed” and you still feel terrible, your iron deserves a look.

Low Ferritin Symptoms to Watch For

Low iron symptoms overlap heavily with low thyroid symptoms, which is exactly why one can hide behind the other. These can all prompt an iron evaluation:

• Fatigue that doesn’t improve with sleep
• Getting winded or a racing heart with mild exertion
• Hair shedding or thinning across the scalp
• Brain fog and trouble concentrating
• Restless legs at night
• Craving ice or chewing on ice

Hair loss is what most women search for. A 2022 meta-analysis found lower ferritin in women with nonscarring hair loss, although no ferritin level has been shown to guarantee regrowth. These symptoms have other causes too, which is why testing matters.

The Tests to Ask For

Ask your provider for more than a CBC. A ferritin estimates your stored iron. Serum iron, TIBC, and transferrin saturation show how much iron is circulating and available. hs-CRP helps show whether inflammation might be propping up your ferritin.

If you have Hashimoto’s, a full thyroid panel (TSH, free T4, free T3, and thyroid antibodies) gives a more complete picture than TSH alone. Many conventional guidelines consider TSH and free T4 sufficient, but in our practice we find free T3 and antibodies useful for understanding how a patient is actually doing.

How to Increase Ferritin Levels Safely

Test before you supplement. Iron is not a “more is better” nutrient. Excess iron is harmful, and some people carry genes for iron overload without knowing it.

Find out why it’s low. Heavy periods, low intake, and poor absorption are the usual reasons. If you’re a man or a postmenopausal woman with unexplained iron-deficiency anemia, your doctor should evaluate you for gastrointestinal blood loss. If you don’t address the reason, your ferritin will drop again once you stop supplementing.

Eat the iron your body absorbs best. Heme iron from red meat, liver, and shellfish is absorbed much better than the iron in plants. Pairing plant sources like lentils and greens with vitamin C helps, although food alone often isn’t enough to correct an established deficiency.

Mind the timing. Coffee, tea, and calcium reduce iron absorption. If you take levothyroxine, keep iron supplements at least four hours away from your dose, because iron reduces how much thyroid medication you absorb.

Work with your practitioner on the schedule. Iron triggers a hormone called hepcidin that temporarily shuts down further absorption. Women absorb more iron per dose when they take it every other day, but a 2025 trial found daily dosing raised blood counts more over time. The right schedule depends on your numbers.

Retest. If you’re anemic, hemoglobin is usually rechecked within two to four weeks. Rebuilding ferritin stores takes longer, often a few months.

When Your Thyroid Treatment Isn’t the Whole Answer

Correcting a confirmed iron deficiency won’t fix every symptom. But it’s inexpensive to test, frequently overlooked, and in women with Hashimoto’s it’s one of the first things worth ruling out when medication alone hasn’t brought you back to feeling like yourself.

At RedRiver Health and Wellness, we look at iron status, thyroid function, inflammation, and gut health together, because in women with Hashimoto’s they’re rarely separate problems.

References

1. Snook J, Bhala N, Beales I, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. 2021. Supports non-anemic iron deficiency, symptom patterns, common causes, and when GI evaluation is warranted Snook2021.
2. World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. 2020. Best fit for ferritin thresholds in the setting of inflammation. The article’s inflammation caveat needs a population guidance source like this, even though no indexed sentence is provided here.
3. Garofalo V, Condorelli RA, Cannarella A, et al. Relationship between Iron Deficiency and Thyroid Function: A Systematic Review and Meta-Analysis. Nutrients. 2023. Supports an association between iron deficiency, lower thyroid hormone measures, and thyroid autoantibody positivity, while keeping the wording appropriately cautious Garofalo2023.
4. Köhrle J. Selenium, Iodine and Iron–Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism. International Journal of Molecular Sciences. 2023. Best source for the mechanistic claim that thyroid peroxidase is iron-dependent and for the bidirectional link between iron status and thyroid physiology Köhrle2023.
5. Weyand AC, Chaitoff A, Freed GL, et al. Prevalence of Iron Deficiency and Iron-Deficiency Anemia in US Females Aged 12–21 Years, 2003–2020. JAMA. 2023. Best prevalence citation for the article’s point that iron deficiency is much more common than iron-deficiency anemia in young females Weyand2023.