Low Ferritin in Runners: What Your Labs Actually Say and When to Test

Episode: S6E28 | Guest: Callie Roseland, MS, RD, CSSD | Aired September 10, 2026 | 64 min

Author: Nick Klastava

Podcast Hosts: Nick Klastava & Amanda Katz

Listen: Spotify | Apple Podcasts | YouTube

Low ferritin in runners is the one lab value the internet has decided we all need to care about, and it is also the one most of us understand the least. You see a number. You compare it to a number some influencer posted. You buy the supplement she takes. That is the entire decision process for a lot of runners, and it is a bad one. This week Coach Amanda and I sat down with Callie Roseland, a sports dietitian who works with endurance and mountain athletes, to take apart what iron and ferritin actually are, what a full panel tells you that one number never will, and why supplementing off a single result can be genuinely dangerous. Callie is an exercise physiologist by training who became a registered dietitian, spent seven years as a performance dietitian in the special operations military community, and now runs her own practice. She was the right person to ask, and she did not give us a supplement recommendation. She gave us a set of questions.

Key Takeaways

• Ferritin is one number on a panel, not the panel. A full iron studies workup includes ferritin, serum iron, TIBC, transferrin saturation, and a CBC. Reading one of those in isolation is how runners make bad decisions.

• Supplementing off a low ferritin alone can be harmful. You can have a ferritin of 15 and a serum iron of 150. Excess circulating iron is inflammatory and toxic, and your body has no easy way to dump it.

• Low ferritin in runners is multifactorial. Increased training demand, iron lost in sweat, altitude, monthly blood loss, undiagnosed GI issues, plant based eating, underfueling, and poor absorption all feed into it.

• There are three stages, not one. Stage one is depleted stores with normal iron labs. Stage two is iron deficiency without anemia. Stage three is iron deficiency anemia, where hemoglobin finally drops and oxygen transport is substantially impaired.

• A ferritin of 15 can be labeled normal by a lab and still be a problem for you. Callie's performance minimum is around 40, and she would rather see 50, especially for anyone training at altitude.

• When you get tested matters as much as whether you get tested. Ferritin is an acute phase reactant, so inflammation from a race or hard weekend can falsely elevate it. Avoid the first few days of your menstrual cycle too.

• Absorption is a timing problem. Coffee, tea, and dairy inhibit it. Vitamin C helps it. Hepcidin rises with acute inflammation after hard training, which is why iron is usually taken early, on an empty stomach, away from the session.

• Iron is a performance supplement, not a foundational one. If you need it forever, that is the signal to go find out what is actually going on underneath.

Low Ferritin in Runners Is Only One Number on the Panel

Callie's first move was to zoom out, and it is the move most runners skip. Iron is not just about stores. It is about how iron comes into the body, how it moves around, how it gets stored, and how it interacts with everything else. Ferritin only answers one of those questions.

So when she orders labs, she orders a full iron studies panel. Ferritin is your storage form. Serum iron is the iron circulating in your blood at the moment of the draw. TIBC, or total iron binding capacity, tells you how much transferrin is available to bind to iron. Transferrin is the protein that transports iron through your cells. Transferrin saturation, sometimes written as TSAT, is the percentage of those binding sites actually occupied, and it gets calculated from your serum iron and TIBC together.

Her analogy is the one I am going to steal. Ferritin is your savings account. Transferrin is your checking account, the money moving in and out. Looking only at savings tells you nothing about whether you can pay rent this month.

Then there is the CBC, the complete blood count, which is not an iron test at all but belongs in the same conversation. That is where hemoglobin lives, which is your oxygen carrying capacity, along with hematocrit, MCV, MCH, RDW, and your white cell counts. It is a timestamp of what is happening in your blood.

Every one of those markers tells you something on its own. None of them tells you enough. And this is where I got a little heated on the recording, because here is the scenario that keeps me up: your ferritin comes back at 15, and nobody checked your serum iron, which is sitting at 150. You start supplementing. That is not a suboptimal decision. That is a potentially dangerous one. Excess circulating iron is inflammatory and harmful, and the body keeps iron on a very tight leash for a reason.

Callie made the point that this is not only a female athlete problem in reverse. She sees higher iron and higher ferritin in a lot of her male athletes, sometimes from diet, sometimes from the simple absence of monthly blood loss, and often from genetics that raise iron levels in a way food will never touch. She has sent male athletes to a hematologist to donate blood specifically to bring those values back down. High iron is not a win.

Why Low Ferritin in Runners Happens in the First Place

Amanda asked the obvious follow up, which is why runners in particular keep landing here. Callie's answer was one word before it was a list: multifactorial.

Training itself raises the demand. More training means more turnover and more overall need. We lose iron through sweat. If you are training at altitude, you need adequate stores just to keep oxygen transport and mitochondrial function doing their jobs under a bigger load. For anyone menstruating, there is regular monthly blood loss layered on top of all of it.

Then the causes get less obvious. Undiagnosed GI issues are a big one. Celiac disease you do not know you have. An H. pylori infection, which will actually feed off the iron you consume. Conditions like endometriosis that change the blood loss picture entirely. Callie has seen all of these turn out to be the real answer after months of a runner blaming their diet.

Intake is the next bucket. Plant based and vegetarian eating patterns make adequate iron harder without a plan. Underfueling, whether it is intentional or the accidental kind that happens when training volume climbs faster than appetite, means you are short on everything, not just iron.

And then absorption, which is the part almost nobody considers. Stress affects digestive capacity. If you cannot digest and absorb what you are eating, the food on your plate is not the food in your cells. Micronutrient deficiencies show up, and iron is one of the most common.

Most runners know that vitamin C and iron go together. Fewer know that vitamin A, copper, and the B vitamins are all involved in iron metabolism. So the answer to why you have low ferritin might not be iron at all. It might be a co-factor you have never had measured. Which brings you right back to asking better questions before slapping another supplement on the list.

The Three Stages of Low Ferritin in Runners

This was the section where I learned the most, and I have done a lot of reading on iron over the years. Most people treat this as binary. You have anemia or you do not. Callie framed it as a progression, and once you see it that way the whole thing makes more sense.

Stage one is depleted stores. Your iron labs look normal. Your ferritin is suboptimal or low. Your reserves are drained but nothing else has broken yet. Some people feel it here as fatigue or hair loss. Plenty of people feel nothing.

Stage two is iron deficiency without anemia. Red blood cell production and iron supply start declining, but hemoglobin holds relatively steady, which is exactly why a basic panel misses it. At the cell level you are looking at impaired oxidative enzymes, impaired respiratory proteins, and reduced immune function. Perception of fatigue really picks up here. This is where athletes usually start noticing that training feels harder and adaptations are not showing up.

Stage three is iron deficiency anemia. Hemoglobin finally drops on the lab report. Oxygen transport is substantially impaired. For a runner this is the floor, and at altitude it gets worse faster because the demand for oxygen is already elevated.

The symptom list across all three stages is frustratingly vague. Chronic fatigue. Afternoon fatigue. Hair loss. Cold sensitivity. Declining performance, especially at faster paces. Callie flagged that these overlap heavily with thyroid issues, which is another argument for testing comprehensively rather than chasing one marker.

And here is the runner problem. We are extremely good at feeling our bodies and extremely bad at acting on what we feel. Most of my athletes who find out their ferritin is at 5 tell me they have been dragging for six weeks. We push through, and then a wheel comes off, and only then do we test.

What Optimal Ferritin Actually Looks Like

Lab reference ranges for ferritin are enormous, and they are not built around athletic performance. They are built around not being clinically ill. Callie also pointed out that ranges shift slightly between labs, so if you move and your new provider uses a different lab, a small change in your number might be the lab, not you.

You can walk out of an appointment with a ferritin of 15 and a green light, while sitting squarely in the symptom set we just went through. That is the gap.

Under a performance lens, Callie's minimum is around 40. What she would rather see is 50, and she is especially firm about that for athletes training at altitude. She is not chasing a big number. She wants a tighter window, because high ferritin brings its own problems. Get to 50 and most of the symptoms tend to slide off.

Food First, Including the Beef Liver Cubes

Callie's supplement philosophy is food first, but not food only, and she started with the food.

Heme iron, the animal based form, absorbs at a higher rate. Lean meats and organ meats are the headliners. Organ meats do double duty, because they also carry the vitamin A and copper that iron metabolism depends on.

Then she told us what she actually does, and Amanda knew it was coming. Callie buys high quality beef liver from a butcher or the meat counter, blends it in a high powered blender until it is liquid, pours it into small silicone ice trays, and freezes it. When she is cooking ground beef, ground turkey, or pasta sauce, she drops one to three cubes in and cooks it down into the food. Her words: she treats herself like a toddler and hides the nutrient dense option where she will not taste it. It is also how she keeps herself off an iron supplement.

For plant based runners, non heme iron is the game, and pairing matters more. Vitamin C sources like bell peppers and tomatoes alongside your iron containing foods improve absorption meaningfully. It is not a hack. It is just how the chemistry works.

What Blocks Absorption, and Why Timing Beats Dosage

Two everyday things inhibit iron absorption, and most runners consume both daily. Coffee and tea, because of tannins. Dairy, because of calcium, which means the Greek yogurt bowl and the glass of milk are working against you if the timing lines up badly.

That does not mean you need to rearrange your entire diet. It means that if you are supplementing, you keep those two hours away from the iron. Callie's framing was that she does not want athletes spending more money on supplements than they have to, so you may as well get the absorption you paid for.

Then there is hepcidin, which I brought up on the episode and Callie explained properly. Hepcidin is a naturally occurring regulator of how iron gets absorbed. When your stores are adequate, hepcidin rises and shuts absorption down, because you do not need more. When you are deficient, it drops to let more in. That is an elegant system right up until you add training to it.

Hepcidin is also tightly regulated by inflammation. Not chronic inflammation, which is its own conversation, but the acute kind that follows a hard session. Inflammation is not the villain the internet has made it out to be. It is how your body repairs itself. But if hepcidin spikes after a hard workout and you take your iron in that window, the two are competing and you absorb far less than you think.

Which is why iron is usually recommended early in the morning on an empty stomach. Nothing competing for absorption, and hepcidin levels are naturally lower before they climb through the day and around training.

On dosing frequency, there is research supporting alternate day supplementation producing equal or better results than daily. Part of that is absorption and part of it is that high dose iron is rough on the gut. If it makes you nauseous, you stop taking it, and a supplement you abandon works zero percent of the time. Callie recommends every other day frequently, but which stage you are in changes the answer, which is the whole argument for having someone read your labs.

When to Get Your Blood Work Drawn

Callie's line for this is test, do not guess. But she was equally clear that a badly timed test is barely better than a guess, because one test is one timestamp.

Ferritin is what is called an acute phase reactant. In plain terms, inflammation can push it up. So if you race on Saturday, run long on Sunday, and get labs drawn Monday morning, your ferritin can come back falsely elevated by the previous 48 hours. It reads 75 when your true number would have you below the performance threshold, and nobody flags it, and you go another six months feeling terrible with a normal lab in your file.

Same logic applies to your menstrual cycle. Callie does not test anything iron related in the first few days, because of the blood loss. She shifts it to roughly a week after. Most physicians do not think about this and will hand you an order for three o'clock this afternoon because you happen to be in the office.

If you already got labs drawn without any of this in mind, do not panic and do not throw the results out. Just be able to answer the questions: what day of your cycle was it, were you fasted, what did training look like in the 48 hours before, what medications or supplements were you on, how hydrated were you. Those answers are what turn a number into information.

How Often Runners Should Test

Bare minimum, once a year. What Callie actually pushes for is comprehensive labs every six months, and comprehensive means more than iron studies. Other nutrient panels, other markers, the things that affect both general health and performance.

She tightens that window for specific situations. If you are female. If you have any history of the stages above in the last one to two years. If you are sitting at suboptimal ferritin even without a diagnosis. If you know you are heading to altitude or into a hard training block in the next three to six months. If you have a history of underfueling or a restrictive diet, whether that is by choice or by necessity like gluten free for celiac.

And if you are actively correcting something, six months is too long to wait to find out it did not work. Her preference there is every three months, so you can either confirm the plan is moving the needle or pivot before you have burned half a year.

Testing Around a Hard Training Block

I pushed on this because the pattern I see with athletes is so consistent. You finish a race, you base build at low intensity, and everything is fine. Then the block ramps. The workouts get hard, the long runs get long, and six weeks in you are wrecked. That is when you test. That is when you find the low ferritin. And by then you cannot tell whether the fatigue is training fatigue or a biomarker problem.

Callie's fix is to move the test earlier. If you are not routinely testing, back up three months from the start of a big block and get a baseline. Now you know whether you are already floating near the danger zone before you add the load, and you have something to compare against later.

Going into that block, your iron needs go up. Bigger turnover, bigger losses. So you look at daily dietary intake first. But she was insistent that the fatigue question is never just iron. What is the training doing to your sleep. What does food quality look like. Are you doing anything to support your nervous system. And above all, are you fueling enough, which means something different for every athlete. It could be total energy, it could be carbohydrate specifically, it could be protein. Stress is stress, and your body does not file it into separate categories.

Her closing point on this was the one I would underline. For most runners heading into higher training, the answer is checking whether carbohydrate intake actually matches the energy output. That is usually the bigger lever than the supplement.

Low Ferritin in Runners Is Not a Lifelong Supplement Problem

I asked Callie the question I have never had a clean answer for. Is supplementing the answer forever, or is it a band aid over something else.

Her answer: iron is a performance supplement, not a foundational one. Most athletes probably need one to three foundational supplements day to day. Iron is not on that list. It can be genuinely performance supportive, and it should not be a 24/7, 365 fixture of your life.

Then she described the cycle, and I have watched athletes live it. Labs come back low. They start supplementing, sometimes because a provider said so, sometimes because AI or someone online said so. They feel better, which is real and which matters, because chronic fatigue is miserable. Labs improve. They come off it. Six months later the fatigue creeps back and they start again. Round and round.

Callie's question in that moment is always the same. Why do you need this in the first place. Because something is driving it. Chronic underfueling, intentional or not. Training volume. A GI issue. Another micronutrient gap. She has taken athletes off iron entirely, found the actual cause, and watched them never need to supplement again.

She was careful to say she is not telling you iron is bad or that you should not supplement. She is telling you that needing it repeatedly is information, and most runners never stop to read it.

Stop Handing Your Labs to Your PCP Alone

Amanda made the most forceful argument of the episode and I am not going to soften it. There is real harm in interpreting your own results, and there is real harm in getting supplement guidance from someone who does not know what an endurance athlete needs.

She described a runner who was put on the wrong form of iron by a well meaning provider, developed GI issues during long runs, and became afraid to fuel her long runs at all. A sports dietitian course corrected it and the problem went away. That is what a scope of practice gap costs in practice.

Her pitch, and it is mine too: we invest in carbon plated shoes, race entries, and the outfit. Take three minutes off scrolling past an influencer explaining what raised her ferritin, and put that time and money toward the right professional instead. Amanda and I have both worked with sports dietitians and it changed things for both of us.

None of this is a knock on primary care. My PCP has told me plainly that a ferritin of 20 is within range but that I am an endurance athlete and he is not going to speak on something outside his expertise. I have always respected that, because the alternative is a confident answer from someone operating outside their lane. You see an orthopedist for orthopedic problems. Sports dietitians exist for exactly this.

Callie framed it through a model she used in the military performance world: proactive, active, and reactive. Investing before there is a problem is the proactive lane, and it is the cheapest one. Waiting until something breaks means spending more money, more time, and often more of both than you would have needed.

On AI, she was measured. There is some value there, and a lot of people feel jaded by traditional medicine for understandable reasons. But general primary care providers frequently do not have a performance background, so they are not asking the right questions, which means they are not getting the right answers. Neither is a chatbot reading your PDF. Find the people who can speak your language.

Guest Bio

Callie Roseland, MS, RD, LDN, CSSD, IFNCP, EP-C is a Sports Dietitian who specializes in helping endurance and mountain athletes fuel for performance, recovery, and long-term health. She has 9+ years of experience in high-level performance nutrition, including more than 7 years as a Tactical Performance Dietitian supporting U.S. Special Operations Forces within a multidisciplinary human performance team.

Through her private practice, Fueling Upward, Callie works with adult athletes who lift, run, and climb mountains while balancing serious training with full-time work, family, and real life. Her background in exercise physiology, sports nutrition, and integrative and functional nutrition allows her to take a comprehensive approach to performance, with particular interests in endurance fueling, performance labwork, gut health, hormone health, injury recovery, and optimizing nutrition to support high-level training and performance.

Fueling Upward offers 1v1 virtual nutrition coaching, group education, and on-demand resources to help athletes have more energy, ditch gut issues, and fuel the training it takes to cross finish lines and climb mountains.

Email: callie@fuelingupward.com

IG: @fueling.upward.rd

Website: www.fuelingupward.com

Frequently Asked Questions

What is the difference between low ferritin, iron deficiency, and anemia?

They are three stages of the same progression. Stage one is depleted stores, where ferritin is low but your other iron labs and hemoglobin look normal. Stage two is iron deficiency without anemia, where red blood cell production and iron supply decline while hemoglobin holds, and where fatigue and stalled training adaptations usually show up. Stage three is iron deficiency anemia, where hemoglobin drops and oxygen transport is substantially impaired.

What is a good ferritin level for a runner?

Lab reference ranges will call 15 normal, but that range is not built for performance. A performance minimum is around 40, with roughly 50 being the preferred target, and altitude training pushes that higher rather than lower. Very high ferritin is not the goal either.

Why is low ferritin in runners so common?

It is multifactorial. Training raises iron needs, you lose iron through sweat, altitude increases demand, menstruation adds monthly blood loss, and undiagnosed GI issues like celiac or an H. pylori infection can quietly drain stores. Plant based eating, underfueling, and poor absorption driven by stress all compound it.

When should I get my iron labs drawn?

Morning, fasted, and not within 48 hours of a race or a hard training weekend, because inflammation can falsely elevate ferritin. If you menstruate, avoid the first few days of your cycle and shift the draw to roughly a week after. Keep the conditions consistent so you can compare across tests.

Should I take iron every day or every other day?

There is research supporting alternate day supplementation producing equal or better results, partly because high dose iron is hard on the gut and daily dosing hurts compliance. The right answer depends on which stage you are in, which is why the decision should follow a full panel rather than a single ferritin number.

Can I just start taking iron if my ferritin is low?

No. You can have low ferritin and high circulating serum iron at the same time, and supplementing into that is potentially toxic rather than merely unhelpful. Get a full iron studies panel including serum iron, TIBC, transferrin saturation, and a CBC, and have someone who works with athletes interpret it.