Low Ferritin: Why Your Iron Stays Low and How to Raise It

By Dr. Sarah Khan, PhD, MBA
Functional Nutritionist NYC | Hashimoto's, Hormone, Autoimmune & Gut Health Specialist

Low ferritin is one of the most common lab findings I see, especially in menstruating women, and it is also one of the most commonly under-treated. It can drive fatigue, hair shedding, weakness, brain fog, feeling cold all the time, headaches, dizziness, shortness of breath, and restless legs.

The part most people miss is this: you can have low iron stores even if you are not anemic. Your hemoglobin can come back perfectly normal while your reserves are running on empty. That is exactly why ferritin matters, and why "your bloodwork looks fine" is not always the end of the conversation.

What is low ferritin?
Ferritin is the protein that stores iron in your body. A ferritin below 30 ng/mL is generally considered consistent with iron deficiency, and below 15 ng/mL suggests depleted stores. Because ferritin falls before hemoglobin does, low ferritin can appear months or years before anemia shows up.

What Is Ferritin, and How Is It Different From Iron?

Iron is an essential mineral your body uses to make hemoglobin, carry oxygen, produce energy, and support muscle and brain function. When iron runs low, delivering oxygen and generating energy both become harder.

Ferritin is the protein your body uses to store that iron. An easy way to hold the difference:

• Iron is the money in your wallet, the iron currently being transported and used.
• Ferritin is the money in your savings account, your stored reserves.

You can drain savings for a long time while your wallet still looks fine. That is iron deficiency without anemia, and it is why ferritin is the earlier and more sensitive marker.

Low Ferritin Symptoms

Symptoms of low iron stores often show up well before a standard anemia diagnosis:

• Persistent fatigue that sleep does not fix
• Hair shedding, especially diffuse shedding across the scalp
• Brain fog and difficulty concentrating
• Feeling cold when others are comfortable
• Shortness of breath on stairs or during exercise
• Dizziness or lightheadedness
• Headaches
• Restless legs at night
• Pale skin, brittle nails, or unusual cravings for ice

These overlap heavily with thyroid symptoms and with many other overlooked causes of chronic fatigue, which is one reason ferritin and a full thyroid panel are worth looking at together, particularly in Hashimoto's and other thyroid conditions.

What Ferritin Level Is Considered Low?

Ferritin ranges vary by laboratory and clinical situation. In general:

Two important caveats. First, there is no universally accepted functional medicine ferritin range, so treat that last row as a clinical preference rather than an established cutoff. Second, ferritin is an acute phase reactant, meaning it rises with inflammation. A "normal" ferritin in someone with active inflammation can mask real deficiency, so it should never be interpreted in isolation.

What Labs Should You Check for Iron Deficiency?

A single serum iron result tells you very little. A more complete iron workup includes:

• Ferritin
• Serum iron
• TIBC (total iron binding capacity)
• Transferrin
• Transferrin saturation
• Hemoglobin and hematocrit
• RBC count, MCV, MCH, RDW
• CRP or hs-CRP

Looking at the full pattern is far more useful than looking at any one marker alone. Transferrin saturation combined with ferritin and CRP is usually where the real story lives.

What Causes Low Ferritin? Four Root Causes

Low ferritin almost always traces back to one or more of four issues. Identifying which one is driving your case is the difference between a fix that holds and one that unravels the moment you stop supplementing.

1. You Are Not Getting Enough Iron

Heme iron (from animal foods, generally absorbed more efficiently):

• Beef, lamb, liver
• Oysters, mussels, clams
• Sardines
• Poultry

Plant-based iron (non-heme, absorbed less efficiently but still valuable):

• Lentils, beans, chickpeas
• Tofu and tempeh
• Pumpkin seeds, tahini
• Spinach, quinoa

If you eat little to no red meat, plant-based iron can absolutely meet your needs, but it takes more intention around pairing and timing. More on that below.

2. You Are Losing Too Much Iron

Ongoing loss is the most frequently missed cause. Common sources:

• Heavy menstrual bleeding
• Fibroids or adenomyosis
• Gastrointestinal bleeding
• Frequent blood donation

If blood loss is the driver, iron supplementation alone becomes a treadmill. You replace what you lose and never build reserves. This is particularly worth investigating alongside shifting hormonal patterns in perimenopause, when bleeding often becomes heavier and less predictable.

3. You Are Not Absorbing Iron Well

This is the category I see most often in my practice, and the one conventional workups tend to skip. Conditions and factors that interfere with iron absorption include:

• Celiac disease
• Inflammatory bowel disease
• H. pylori infection
• Autoimmune gastritis
• Low stomach acid, including from long-term proton pump inhibitor use
• Bariatric surgery or prior GI surgery
• Other gut health disorders, including SIBO

Iron is absorbed primarily in the duodenum and requires adequate stomach acid to be converted into an absorbable form. Anything that disrupts that environment disrupts iron status. When ferritin stays stubbornly low despite consistent supplementation, absorption is where I look first.

4. Inflammation Is Affecting Iron Metabolism

Inflammation increases a hormone called hepcidin. Higher hepcidin makes it harder for your body to both absorb iron and release stored iron into circulation. This creates a distinctive pattern:

• Serum iron is low
• Transferrin saturation is low
• Ferritin looks normal or even elevated

This is why CRP or hs-CRP belongs on the panel. Without it, you can easily conclude iron status is fine when the iron is simply locked away and unavailable. This pattern is common in autoimmune conditions and any state of chronic low-grade inflammation.

Nutrients That Help Your Body Use Iron

Iron does not work alone. Several nutrients support its absorption, transport, and conversion into healthy red blood cells.

Vitamin C

Vitamin C substantially improves absorption of plant-based iron. Pair iron-rich foods with bell peppers, citrus, kiwi, strawberries, tomatoes, broccoli, or a squeeze of lemon.

Simple pairings: lentils with lemon, or spinach with bell peppers.

Vitamin A

Vitamin A plays a role in normal iron metabolism and helps mobilize stored iron. Food sources include eggs, salmon, liver, dairy, carrots, sweet potatoes, pumpkin, and spinach.

High-dose vitamin A supplements should not be used routinely, as excessive vitamin A can be harmful.

Copper

Copper is essential for normal iron transport. Low copper can quietly interfere with your body's ability to move and use iron even when iron intake is adequate. Sources include oysters, shellfish, liver, cashews, sesame seeds, sunflower seeds, mushrooms, and dark chocolate.

One consideration worth flagging: high-dose zinc supplementation taken long term can reduce copper absorption. If you have been on standalone zinc for months, that is worth revisiting.

B12 and Folate

Both are required for healthy red blood cell production, and deficiencies can cause anemia even when iron is adequate. B12 comes from fish, meat, eggs, and dairy. Folate comes from leafy greens, lentils, beans, avocado, and broccoli.

Vitamin B6

B6 contributes to hemoglobin production. Sources include salmon, tuna, poultry, chickpeas, potatoes, and bananas.

Protein

Adequate protein matters because your body needs amino acids to build hemoglobin, enzymes, and the transport proteins that carry iron where it needs to go. Under-eating protein while supplementing iron is a common and fixable mismatch.

How to Raise Ferritin: 7 Practical Steps

If your ferritin is low, the goal is twofold: replace the iron, and identify why it dropped in the first place.

1. Eat iron-rich foods regularly. Build heme or plant-based iron into meals throughout the week rather than relying on occasional large servings.

2. Add vitamin C to plant-based iron. This is the single highest-leverage food pairing for non-heme iron absorption.

3. Keep coffee and tea away from iron. Polyphenols and tannins meaningfully reduce absorption. Separate them from iron-rich meals and supplements by at least an hour, ideally two.

4. Separate calcium and iron. Large calcium doses interfere with iron absorption when taken at the same time. Move calcium supplements or dairy-heavy meals to a different part of the day.

5. Consider an iron supplement if indicated. Common forms include ferrous sulfate, ferrous gluconate, ferrous fumarate, and iron bisglycinate. Iron bisglycinate is often better tolerated by people who experience constipation or nausea on other forms. Emerging research also suggests that alternate-day dosing may improve fractional absorption compared with daily or twice-daily dosing, because it avoids the hepcidin spike that follows a dose. Dosing and form should be guided by lab testing and individual tolerance.

6. Check for other nutrient deficiencies. If ferritin is not improving, evaluate vitamin A, copper, B12, folate, and B6 status rather than simply escalating the iron dose.

7. Look for the root cause. Persistent low ferritin warrants evaluation for heavy periods, celiac disease, H. pylori, GI blood loss, inflammatory bowel disease, malabsorption, and chronic inflammation.

Why Isn't My Ferritin Increasing Even Though I Take Iron?

This is the question I get most often, and the answer is almost never "take more iron." Work through these instead:

• Am I still losing iron? Heavy periods or occult GI bleeding will outpace almost any oral dose.
• Am I absorbing it? Low stomach acid, celiac disease, H. pylori, and gut inflammation all block absorption at the source.
• Am I taking it with coffee, tea, or calcium? Timing errors alone can cut absorption dramatically.
• Is inflammation raising hepcidin? If so, iron is going in but staying locked in storage.
• Do I have a co-existing deficiency? Copper, vitamin A, B12, or folate deficiency can stall the entire process.
• Is there an undiagnosed GI condition? This is the most common answer when everything else has been ruled out.

Increasing the dose without answering these questions usually produces more side effects and no more ferritin. It is the same pattern I see with gut supplements that are not working: the product is not the problem, the unaddressed root cause is.

When to Seek Further Evaluation

Talk to a clinician promptly if you have low ferritin along with any of the following:

• Black, tarry, or visibly bloody stools
• Unexplained weight loss
• Chest pain, racing heart, or shortness of breath at rest
• Ferritin that continues to fall despite consistent supplementation
• Low ferritin in a man or a postmenopausal woman, which generally warrants GI evaluation

Frequently Asked Questions

What is a dangerously low ferritin level?

There is no single number that defines danger, but ferritin below 15 ng/mL indicates depleted iron stores, and levels in the single digits alongside symptoms such as chest pain, resting breathlessness, or a racing heart warrant prompt medical evaluation.

Can you have low ferritin with normal hemoglobin?

Yes, and it is common. Ferritin reflects stored iron and falls first. Hemoglobin does not drop until stores are largely exhausted, which means you can be symptomatic with iron deficiency for a long time while standard anemia screening looks normal.

How long does it take to raise ferritin levels?

Rebuilding stores generally takes several months rather than weeks. Most people recheck labs around 8 to 12 weeks into consistent repletion, with full restoration often taking three to six months or longer, depending on the underlying cause and whether ongoing losses have been addressed.

Does low ferritin cause hair loss?

Low ferritin is associated with diffuse hair shedding, and it is one of the first things worth checking when shedding is the primary complaint. Hair regrowth typically lags behind lab improvement by several months, so patience is part of the protocol.

Should I take iron every day or every other day?

Research on hepcidin suggests that alternate-day dosing may improve absorption compared with daily dosing, since a dose of iron raises hepcidin for roughly 24 hours and blunts uptake of the next one. This should be individualized based on your labs, severity, and tolerance.

Can coffee really affect my iron levels?

Yes. Coffee and tea contain compounds that bind iron and reduce absorption significantly when consumed with an iron-containing meal or supplement. Separating them by an hour or two is a small change with a real effect.

The Bottom Line

Low ferritin means your iron reserves are running low. But raising ferritin is rarely as simple as taking more iron.

Healthy iron status depends on iron, vitamin C, vitamin A, copper, B12, folate, B6, and adequate protein working together. It also depends on your ability to absorb iron and on whether you are continually losing it.

If your ferritin stays low despite supplementation, the most important question is not "how much iron should I take?" It is why is this happening? Identifying the underlying cause is what builds iron stores that actually hold.

This article is for educational purposes and is not a substitute for individualized medical care. Iron, copper, and vitamin A can be harmful in excess, so supplementation should be based on laboratory testing and personalized guidance.