Ferritin Levels for Athletes: Reasons Why “Normal” Isn’t Optimal

Introduction

Ferritin is a laboratory test that measures the body’s iron stores. The lower limit of the standard reference value for ferritin in standard laboratories is typically 15 ng/mL. Standard reference values are defined so that 2.5% of the population statistically falls below the lower limit of the reference value. Near this limit, the normal patient often does not yet become anemic and may often be completely asymptomatic. However, the optimal ferritin levels for athletes differ from the normal population, as near this limit many athletes already suffer from symptoms of iron deficiency, which is often manifested as a decrease in performance. Therefore, the lower limit of the reference value for athletes often has to be considered higher than in the normal population.

Prevalence and Effects of Low Ferritin Levels for Athletes

Iron deficiency represents the most common nutritional deficiency globally, and female athletes face disproportionate risk. It is also common in athletes, especially female athletes.

A large proportion of top-level female athletes often suffer from iron deficiency, and this has been confirmed in several studies. A systematic review indicated that up to 60% of female athletes experience iron deficiency[3]. Another research study of 336 Division I female collegiate athletes found that 57.7% had ferritin levels below 40 ng/mL at their pre-participation physical examination[1]. Furthermore, one landmark study of 165 female collegiate rowers found that approximately 27% had low ferritin (below 20 ng/mL) despite having completely normal hemoglobin levels[2]. These low ferritins do not usually make patients anemic, so these values are missed in standard tests when only examining the hemoglobin in the blood count.

Furthermore, we know that these non-anemic low iron levels can have a detrimental effect on athletes’ performance. In the study of college rowers, it was found that 2-kilometer rowing times were 21 seconds slower than teammates with normal iron stores—a performance decrement that would determine podium position versus mid-pack finish in competitive racing. Even more striking: performance decrements remained statistically significant when researchers raised the ferritin threshold to 25 ng/mL, well above the clinical deficiency cutoff. Interestingly, athletes with ferritin levels of at least 30 ng/mL showed no performance inhibitions[2].

It seems that low ferritin is not at all unusual, especially in female athletes, and has real significant effects on athletic performance. Furthermore, ferritin in clinical reference ranges alone does not indicate optimal athletic performance.

How Low Ferritin Level Sabotages Athletic Performance Without Causing Anemia

Many patients wonder why low iron can cause decreased performance without actually causing anemia. However, iron has many other functions in the body than just transporting oxygen and forming hemoglobin. Iron is needed for the function of key enzymes in aerobic metabolism. Iron-dependent enzymes that include succinate dehydrogenase, components of the electron transport chain, and cytochrome oxidase transform chemical energy into mechanical energy during oxidative metabolism[2].

This clear effect of iron deficiency on aerobic metabolism is also observed in studies. For example, a systematic review analyzing 23 studies comprising 669 athletes quantified this effect: iron deficiency negatively affects endurance performance by 3-4%. The same review found that maximal aerobic capacity may be compromised in athletes with serum ferritin below 15-16 μg/L, even when hemoglobin concentrations remain normal[3].

Therefore, correcting iron deficiency may be beneficial for an athlete’s performance, even if the patient does not actually have anemia.

Mechanisms Leading to Iron Deficiency

Iron deficiency can occur in several different ways. Women and athletes are particularly vulnerable, as iron deficiency can develop through various mechanisms:

Menstrual losses

Normally, during menstruation, female patients can typically lose 15–40 mg of iron per menstrual cycle. However, there is great individual variation in the amount of menstruation, and heavy menstruation may increase iron loss[7].The study of Division I athletes found that oral contraceptive use was associated with higher ferritin levels, suggesting menstruation represents a significant iron loss pathway[1]. However, direct evidence that contraceptives directly or indirectly improve an athlete’s performance is weak. So, the conclusion that can be drawn from this study is that lower ferritin is likely to be related to menstruation, but the effect on performance cannot be concluded based on this data.

Foot-strike hemolysis

A less familiar cause of anemia in athletes is foot strike hemolysis. This means that the mechanical shock and compression that occurs when the sole of the foot hits the ground damages red blood cells. When this happens frequently and over a long period of time, it can gradually lead to anemia as a result of the progressive breakdown of red blood cells. Research demonstrates that foot-strike represents the major cause of hemolysis during running, with significantly greater red blood cell destruction in runners compared to cyclists performing equivalent exercise intensity[4]. Therefore, important anamnestic information includes the patient’s sport, the amount of training, and the amount of repetitive impact load on the soles of the feet.

Gastrointestinal blood loss

High-intensity or prolonged exercise can cause small microtraumas to internal organs, which in turn can lead to gastrointestinal, mostly microscopic, leakage, especially when the exercise is prolonged and repetitive[8]. Presumably, the amount of microscopic bleeding is small, but direct comparative studies systematically comparing it with other causes of iron loss have not actually been conducted.

Inflammatory hepcidin response

Physical exercise is a stress on the body, and like other stresses, physical exercise causes an inflammatory response. Exercise triggers inflammatory cytokines that elevate hepcidin, a hormone that blocks iron absorption in the gut and limits iron utilization from stores. Studies show that high-intensity exercise increases interleukin-6 (IL-6) levels by 6.9-fold, with subsequent hepcidin elevation of 1.7-3.1 times baseline levels during the 24 hours following exercise[5]. Thus, physical exercise itself can make it difficult to absorb iron, which can worsen iron deficiency in athletes and also make it more difficult to correct.

Inadequate dietary intake

Many athletes also follow different diets, especially those competing in weight classes. As a result, an athlete’s dietary iron intake can often be low. In addition, many weight class athletes consume a lot of plant-based non-heme iron, which is generally less well absorbed than animal-based heme iron[9].

Optimal Ferritin Level for Athletes: Evidence-Based Thresholds

So what is the appropriate ferritin level for an athlete? Although the lower limit of reference value for laboratory tests in the normal population is 12-15 ng/mL, the optimal lower limit for athletes is higher.

Absolute Iron Deficiency in Athletes

The general consensus in sports medicine circles is that the lower limit of recommendation for ferritin is <30 ng/mL, particularly when accompanied by symptoms or heavy training loads[9]. This cutoff is in line with other research results. For example, the rower study showed impairments at <25 ng/mL and no performance limitations at ≥30 ng/mL[2]. Therefore, it may be good for general athletes to aim for a ferritin of over 30 ng/mL instead of the normal 12-15 ng/mL.

Pre-altitude Training Targets

High altitude training poses special challenges to the aerobic system. The hypoxic effect of high altitude stimulates erythropoiesis, increasing the need for iron. It is also advisable to correct low iron levels in advance. Thus, some high altitude training protocols recommend achieving ferritin ≥50 ng/mL before altitude exposure due to increased iron demands[10]. Hypoxia also increases the inflammatory response, which further increases the hepcidin effect, which in turn reduces iron absorption. So it is worth preparing for high altitude training in advance by improving iron stores well in advance of the start of high altitude training.

Hepcidin Response in Relation to Iron Storage

We noted above that the inflammatory response caused by exercise increases hepcidin levels, which in turn reduces iron absorption. Normally, and with sufficient iron stores, hepcidin prevents excessive iron absorption, which is a normal physiological phenomenon. However, the magnitude of the patient’s iron stores regulates the strength of the hepcidin response. Research shows that athletes’ iron stores dictate both baseline hepcidin levels and the magnitude of post-exercise hepcidin response, with low iron stores suppressing post-exercise hepcidin but also limiting the body’s ability to regulate iron metabolism effectively[6]. The attenuation of the hepcidin response is a physiological phenomenon and describes the fact that there is not enough iron stores and its absorption is not inhibited.

How to Test Ferritin Level for Athletes

Despite the high prevalence of iron deficiency, routine testing of iron levels in athletes is still quite rare. For example, the Division I athlete study found that routine ferritin testing is uncommon at most institutions, despite the high prevalence of low iron stores[1]. According to some recommendations, it would be a good idea to test iron levels at least once a year, but in risk groups, testing may even be recommended quarterly[10]. However, more important than the timing of testing is just to test regularly, as simply monitoring iron levels is rare in many places.

Evidence-Based Supplementation Strategies

So what is the appropriate amount of iron supplement and how should you take it? Iron supplementation is fundamentally individual and should be assessed with your doctor, but based on research evidence, there are some indicative reference values that can be utilized.

The Pengelly systematic review demonstrated that oral supplementation with 100 mg elemental iron daily for 42-56 days improves endurance performance by 2-20% in iron-deficient female athletes[3]. Maximal aerobic capacity improved 6-15% following protocols ranging from 16-100 mg/day elemental iron for 36-126 days[3].

In practice, the common dosages for iron supplementation are 50–100 mg per tablet, and in many clinical situations, in my experience, they are prescribed either one tablet per day or every other day, depending on how well the stomach tolerates it. Depending on the clinical situation, the duration of the course is often a few months. Usually, after a few months of treatment, iron levels are checked, and the decision to continue supplementation is made based on the results.

Parenteral iron supplementation often produces an even more effective response than oral iron supplementation, but at least in Finland its use is strictly limited to medical indications. It is therefore not usually included in measures aimed at improving the performance of athletes. However, for example in women with severe anemic menstruation, parenteral iron therapy may be necessary if oral iron is not sufficient or causes significant harm[11].

Beyond Supplementation: Dietary Strategies

Instead of starting iron supplements straight away, it is also worth paying attention to your diet, as dietary iron is generally absorbed more physiologically and evenly compared to iron supplementation[12]. It also matters a lot where the iron you get from food comes from, as dietary iron comes in two forms with markedly different bioavailability:

Heme iron (from animal sources):

Absorption rate: 15-35%[12]
Sources: Red meat, poultry, fish
Not inhibited by dietary factors
Most efficient way to maintain iron stores

Non-heme iron (from plant sources):

Absorption of non-heme iron varies greatly and is typically significantly weaker than that of heme iron[13].
Sources: Legumes, dark leafy greens, fortified cereals
Absorption inhibited by phytates, calcium, polyphenols
Absorption enhanced by vitamin C, animal protein

However, dietary treatment alone is often insufficient for athletes with iron deficiency. Iron supplementation should also be considered, especially when the patient is exercising a lot, given the exercise-induced hepcidin response[5], or has other stressors, such as heavy menstruation.

Summary

Ferritin is used to measure the body’s iron stores. The typical laboratory reference value is 12–15 ng/mL, which is mostly a statistical value, below which about 2.5 percent of the population falls. Thus, the lower limit of ferritin is not optimized for the athlete or the athlete’s performance, but is purely a reference value for the general population. In general, a lower limit that better describes performance is around 30 ng/mL, and athletes should aim above this value[2][3]. For a more detailed discussion on athlete-specific interpretation of iron studies and sex-specific considerations, see our guides on iron panel interpretation for athletes and female athlete bloodwork.

In athletes, especially female athletes, several factors reduce iron stores. The most common of these is menstrual bleeding, especially when the bleeding is heavy. In addition, iron stores can be reduced by footstrike hemolysis, microscopic gastrointestinal bleeding, and the inflammatory hepcidin response. Dietary iron deficiency is also common in athletes.

Athletes should routinely monitor their iron levels once a year, and in risk groups even quarterly. The need for iron supplementation is individual, but generally 50–100 mg per day or every other day for a few months is quite typical practice. Parenteral iron is effective, but its use usually requires a strict medical indication.

Heme iron from the diet is usually absorbed best or at least better than non-heme iron. In addition, iron from the diet is usually absorbed more physiologically than iron obtained through supplementation. Iron supplementation is often necessary, however, because iron absorption can be low, especially due to the hepcidin response, and without supplementation many athletes, especially women, suffer from iron deficiency.

Ferritin Levels for Athletes: Reasons Why “Normal” Isn’t Optimal

Table of Contents

Introduction

Prevalence and Effects of Low Ferritin Levels for Athletes

How Low Ferritin Level Sabotages Athletic Performance Without Causing Anemia