Let me paint a picture I’ve seen recently of multiple clients…
A woman comes to me who is very active, health-conscious and doing all the “right things.” She works out regularly, eats well, and gets decent sleep…but something still feels off.
She’s tired in a way that doesn’t fully resolve with rest, her hair has been thinning, she feels cold all the time, her mood is flat and her workouts feel harder than they used to.
She’s been to her doctor and was told her labs are “normal”, but nobody looked at her ferritin. If they did, they interpreted it through a lens that often misses the bigger picture.
So, What Is Ferritin and Why Does It Matter More Than Just Looking at Iron?
Most people have heard of iron but fewer understand ferritin. Ferritin is your body’s iron storage protein (think of it like your reserve tank).
When iron intake, absorption, or retention is inadequate over time, your body pulls from that reserve, and ferritin drops, often long before hemoglobin changes enough to flag anemia on a CBC (labs, complete blood count).
Here are a few blind spots I’ve noticed recently:
- You can have depleted iron stores without anemia and still feel terrible.
- Ferritin is one of the most useful early markers of iron status, but it should always be interpreted in context, especially alongside inflammation markers like CRP (C-reactive protein), because ferritin is also an acute-phase reactant (1).
- By the time hemoglobin drops enough to diagnose anemia, iron deficiency has often been building for months or sometimes years. Ferritin usually tells the story much earlier.
“Normal” Ferritin Is Often Not Optimal
This is where things can get tricky.
Many conventional lab ranges flag ferritin as low only below 12–15 ng/mL, but clinically that threshold is often far too low. Multiple randomized controlled trials have shown that women with normal hemoglobin but ferritin <50 ng/mL can still experience significant fatigue and improve with iron treatment (2,3).
A 2023 review in Hematology argued that ferritin reference ranges likely need revision and highlighted that physiologic iron absorption patterns don’t normalize until ferritin exceeds approximately 50 ng/mL (4).
What does this mean?
Your ferritin can be “normal” and still be suboptimal, especially if you’re symptomatic.
What’s Actually Driving Low Ferritin?
Low ferritin is a finding, not a diagnosis but we want to know “why is it low?”
Here are a few things to assess first.
1. Inadequate dietary intake
This is one of the most obvious contributors. Plant-based diets can absolutely be healthy, but they carry higher iron deficiency risk because non-heme iron absorbs at approximately 2–20%, compared to 15–35% for heme iron from animal sources (5). This can matter over time.
Even meat-eaters can fall short if:
- red meat intake is low
- protein intake is inconsistent
- calorie intake is chronically low
2. Poor absorption
You can eat iron and still not absorb it well.
Major blockers include:
- High intakes of coffee, tea or polyphenols with meals and waiting even one hour after a meal can improve absorption significantly (7).
- Calcium at the same meal. Calcium can inhibit both heme and non-heme iron absorption when taken together in sufficient amounts (8). This doesn’t mean avoid calcium, it just means that timing may matter.
3. Gut dysfunction
Iron is absorbed primarily in the small intestine.
Absorption can be significantly impaired with:
- celiac disease
- IBD
- SIBO
- chronic gut inflammation
- low stomach acid
4. High training load
Athletes and active women lose iron through:
- sweat
- GI microbleeding
- increased RBC turnover
- foot-strike hemolysis (especially runners)
A 2024 systematic review of 23 studies found iron deficiency negatively impacted endurance performance and that iron supplementation improved outcomes in deficient female athletes (9).
A separate meta-analysis showed iron deficiency without anemia can impair aerobic adaptation even when hemoglobin remains normal (10). If you’re training hard 4–6 days per week, your needs may exceed baseline RDAs.
5. Heavy menstrual loss
This is one of the most common causes. Heavy bleeding, clotting, fibroids, endometriosis, or simply high-volume cycles can create monthly losses that exceed replacement. This deserves further investigation, not just supplementation.
6. Exercise-induced hepcidin elevation
This one gets missed constantly. Hepcidin is the hormone that regulates iron absorption.
Intense exercise temporarily raises hepcidin, which reduces both iron absorption and iron release from storage (11). A 2022 study found prolonged running increased hepcidin by 51% and reduced iron absorption by 36% post-exercise (12). This matters for supplement timing and for understanding why “eating more iron” sometimes isn’t enough.
The labs that should be assessed alongside iron & ferritin
Patterns matter more than isolated values.
How To Approach Finding The Root Cause for Low Ferritin
Step 1: Find the leak
Determine:
- heavy periods?
- GI issues?
- under-fueling?
- low intake?
- blood donation?
- high training load?
You cannot out-supplement ongoing losses.
Step 2: Increase iron-rich foods
Best absorbed (heme iron):
- red meat
- liver
- oysters
- clams
- dark poultry
Aim for 3–4 servings per week if tolerated.
Non-heme:
- lentils
- beans
- pumpkin seeds
- spinach
- tofu
Step 3: Pair strategically
Vitamin C improves non-heme iron absorption, particularly when meals contain inhibitors (13).
Think:
- beans + salsa
- spinach + citrus
- lentils + tomatoes
Step 4: Spacing can make a difference
Try separating the following from iron-rich meals by 1–2 hours:
- coffee
- tea
- calcium
- high-dose zinc
Step 5: Supplement strategically
Not everyone needs iron and not all iron is tolerated equally.
Emerging research supports alternate-day dosing for better absorption and lower hepcidin response (14,15), which often improves GI tolerance too.
The Bottom Line
Low ferritin is not a minor inconvenience.
It can affect:
- energy
- mood
- hair growth
- recovery
- thyroid function
- exercise capacity
- resilience
Fixing it isn’t just about taking iron, but about understanding why it got low in the first place.
The whole picture matters. If you’ve been told your labs are “fine” but your symptoms say otherwise, it may be worth taking a deeper look.
Disclaimer: Do not start iron supplementation without labs and individualized guidance. Excess iron can be harmful and should always be evaluated in context.
References
- Kell DB, Pretorius E. Serum ferritin is an important inflammatory disease marker. Metallomics. 2014.
- Krayenbuehl PA, Battegay E, Breymann C, et al. Intravenous iron for the treatment of fatigue in nonanemic, premenopausal women with low serum ferritin concentration. Blood. 2011;118(12):3222–3227.
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247–1254.
- Martens K, DeLoughery TG. Sex, lies, and iron deficiency: a call to change ferritin reference ranges. Hematology Am Soc Hematol Educ Program. 2023.
- Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010;91(5):1461S–1467S.
- Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption by polyphenolic-containing beverages. Br J Nutr. 1999;81(4):289–295.
- Ahmad Fuzi SF, et al. A 1-h interval between a meal containing iron and tea attenuates inhibitory effects on absorption. Am J Clin Nutr. 2017.
- Hallberg L, Rossander-Hulthén L, Brune M, Gleerup A. Calcium and iron absorption. Eur J Clin Nutr. 1992.
- Pengelly M, et al. Iron deficiency, supplementation, and sports performance in female athletes: a systematic review. J Sport Health Sci. 2024.
- Burden RJ, et al. Is iron treatment beneficial in iron-deficient but non-anaemic endurance athletes? Br J Sports Med. 2015.
- Larsuphrom P, Latunde-Dada GO. Serum hepcidin and exercise: systematic review. Nutrients. 2021.
- Barney DE, et al. Running increases hepcidin and decreases iron absorption. J Nutr. 2022.
- Cook JD, Reddy MB. Effect of ascorbic acid on nonheme iron absorption. Am J Clin Nutr. 2001.
- Moretti D, et al. Oral iron supplements increase hepcidin and reduce absorption. Blood. 2015.
- Stoffel NU, et al. Alternate day versus consecutive day oral iron dosing. Lancet Haematol. 2017.
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