IngredientsFerritin is a highly conserved, endogenous iron-storage protein found throughout the living world. Ferritin is a class of naturally occurring iron storage proteins, which is ubiquitous in animals, plants, and microbes (except for yeast). Its name derives from the Latin ferratus, meaning "associated with iron." Ferritin was first isolated from horse spleen in 1937 by Victor Laufberger; due to the fact that the protein contained more than 20% by dry weight of iron, it was called "ferritin," i.e., "associated with iron."
Human ferritin is a 24-subunit, 480 kDa, 12 nm globular protein with a hollow center cavity (cavity diameter of 8 nm). One 24-subunit ferritin protein can store up to 4500 iron ions in its hollow center. Each subunit is composed of four α-helices (helix A, B, C, and D) which together form a bundle, and a fifth C-terminal short α-helix (helix E).
Ferritin exists in multiple molecular forms:
Ferritin is a ubiquitous and well-characterized iron storage and detoxification protein, widely distributed in plants, animals, and bacteria. The cellular localization of human ferritin is tissue specific. Ferritins in animal cells are mostly cytosolic soluble proteins, whereas ferritins in plants are mainly found in the non-photosynthetic plastids such as proplastids, etioplasts, chromoplasts, and amyloplasts.
Most reported naturally occurring phytoferritins from various plant seeds—including soybean, pea, black bean, maize, alfalfa, and Arabidopsis—usually consist of two subunits. In legume seeds, more than 90% of iron is stored in the form of ferritin. Legume seeds are a traditional source of plant ferritin.
In animals, ferritin is concentrated especially in the liver, spleen, bone marrow, and skeletal muscle. The groundwork for ferritin discovery was performed by earlier scientists who identified iron deposits in tissues like the liver and spleen. In the late 19th century, scientists such as Perls (1867) discovered iron-containing granules, visible as positive Prussian blue stains, in these tissues. These granules, which contained iron oxide and phosphate, varied in color from pale yellow to brown and were particularly abundant in the spleens of horses, accounting for up to 5% of the organ's dry weight.
In the context of dietary supplementation and food fortification, ferritin is employed primarily in its plant-derived (phytoferritin) form, most often extracted from soybeans and peas. In this complex, ferritin iron (a novel dietary iron source) is masked by a protein coat, so it is less sensitive to chelators, and can be potentially explored as a safe and efficient functional reagent.
Due to the unique properties of plant ferritin, food enrichment with ferritin iron seems to be a promising strategy to prevent iron-deficiency malnutrition. This protein captures huge amounts of iron ions inside the apoferritin shell and isolates them from the environment. Thus, this iron form does not induce oxidative changes in food and reduces the risk of gastric problems in consumers.
Ferritin is also used in its recombinant form as a nanotechnology scaffold in pharmaceutical and vaccine research. Ferritin nanocage has shown promising applications in the biomedical field, such as drug delivery and antigen displaying of vaccines. Its hollow cavity can encapsulate various drugs inside, and the reversible self-assembly property makes it feasible to load drugs in the process of disassembly/reassembly.
The history of ferritin began with a discovery by the Czech scientist Vilem Laufberger, who in 1937 named "ferritin" an iron-rich compound obtained via the crystallization of horse spleen extract. The groundwork for ferritin discovery was performed by earlier scientists who identified iron deposits in tissues like the liver and spleen.
From 1942 to 1946, the group of Leonor Michaelis and Sam Granick published a series of papers on ferritin. Researchers showed that it consists of a protein coat called "apoferritin" and an inorganic mineral core, including up to 4000 iron atoms. Under the influence of low pH, the protein globule disassembles and detaches its inorganic core. In 1943, the ferritin iron-storing functions and its involvement in iron metabolism were shown.
The clinical utility of ferritin as a measurable serum biomarker came considerably later. Quantification of serum ferritin awaited the purification of ferritin and anti-ferritin antibodies and the development of sensitive immunoassay techniques. In 1972, using an immunoradiometric assay, Addison et al. convincingly demonstrated that ferritin could be reliably detected in human serum.
In 1975, Jacobs and Worwood suggested that a serum assay might provide a "useful and convenient method of assessing the status of iron storage." Accordingly, serum ferritin measurement has become a routine laboratory test, although it is now known that many additional factors — including inflammation, infection, metabolic abnormalities, and malignancy — all of which may elevate serum ferritin, complicate interpretation of this value.
Ferritin's unique structural features have recently been exploited for many diverse biological and technological applications. To date, more than 40,000 publications have explored this remarkable protein.
All ferritins have 24 protein subunits arranged in 432 symmetry to give a hollow shell with an 80 Å diameter cavity capable of storing up to 4500 Fe(III) atoms as an inorganic complex. Subunits are folded as 4-helix bundles, each having a fifth short helix at roughly 60 degrees to the bundle axis.
Structural features of ferritins from humans, horse, bullfrog, and bacteria are described: all have essentially the same architecture in spite of large variations in primary structure (amino acid sequence identities can be as low as 14%) and the presence in some bacterial ferritins of haem groups.
Ferritin consists of 24 subunits, typically comprised of different ratios of H and L chain subunits. The ratios vary by organ and even by cell type.
The common property of ferritins is to acquire iron through ferroxidase activity, followed by translocation and hydrolysis to form an inorganic nucleation in the internal cavity. Steps in iron storage within ferritin molecules consist of Fe(II) oxidation, Fe(III) migration, and the nucleation and growth of the iron core mineral. H-chains are important for Fe(II) oxidation and L-chains assist in core formation. Iron mobilization, relevant to ferritin's role as iron reserve, is also discussed.
In plant ferritin, the iron is stored specifically as ferric oxyhydroxide-phosphate. Plant ferritin is composed of 2 types of subunits, H-1 and H-2, which have been shown to be involved in different functions related to the oxidative deposition of iron. However, the ratio of these 2 protein subunits is plant species dependent. This may explain the variation in total iron bound to plant ferritin, which has been reported to vary considerably between different legumes, ranging from 18% in soybeans to 42% in dry peas.
Intracellular iron regulation is mostly facilitated by iron regulatory proteins (IRP) and the hypoxia-inducible factor (HIF) system, which regulate gene translation and transcription, while the most important systemic regulatory mechanism is the so-called hepcidin–ferroportin axis. Insufficient production of hepcidin, the hormone that inhibits cellular iron release through its interaction with the iron exporter ferroportin, results in excess iron release and uptake, leading to systemic iron overload and potential organ damage.
The iron storage protein ferritin plays a key role in iron metabolism. Its ability to sequester the element gives ferritin the dual functions of iron detoxification and iron reserve. The importance of these functions is emphasized by ferritin's ubiquitous distribution among living species.
A tightly balanced iron homeostasis is a physiological necessity, because unbound free iron is a key contributor of toxic potential as a source of oxidative stress via the Fenton reaction and its role in ferroptosis, an iron-dependent form of regulated cell death. Ferritin's core function is to prevent this free iron from causing cellular damage. Iron excess is potentially hazardous as its divalent form (Fe²⁺) generates toxic reactive oxygen species (ROS) via the Fenton reaction, causing oxidative damage to the cells.
While ferritin can be filled to capacity with iron, in reality ferritin can be filled as much or as little with iron as needed. This figure can also be interpreted as different ferritin proteins in environments of different iron concentrations, storing different amounts of iron.
Ferritin iron from dietary sources is absorbed by a mechanism distinct from conventional non-heme iron. Iron absorption from soybean-derived ferritin, an approximately 550-kDa iron storage protein, is comparable to bioavailable ferrous sulfate (FeSO₄). However, the absorption of ferritin is reported to involve an endocytic mechanism, independent of divalent metal ion transporter 1 (DMT-1), the transporter for nonheme iron.
Even a nine-fold excess of FeSO₄ in the diet did not influence absorption of the ferritin iron by humans (4.5 mg of FeSO₄ and 0.5 mg of labeled ferritin iron ⁵⁹Fe) — the ferritin iron bioavailability from such a composed iron source was the same as it was from the diet containing only the ferritin iron. This suggests that these two types of iron do not compete for the same receptor (DMT-1) and are absorbed through different absorption mechanisms.
It was proven that soybean ferritin is absorbed through endocytosis dependent on assembly peptide 2 (AP2). Because ferritin iron is separated from chelating components such as phytates by its protein coat, it is more stable, rendering iron more bioavailable.
Recently, novel pathways such as ferritinophagy and ferroptosis have been discovered, opening perspectives for a better understanding and treatment of iron-related diseases as well as infections and cancer. Ferritin is the intracellular iron storage protein that stores surplus iron after all the cellular needs are fulfilled and releases it in the face of acute demand. Currently, there is a surge in interest in ferritin research after the discovery of novel pathways like ferritinophagy and ferroptosis.
Iron deficiency is the world's most prevalent nutritional deficiency. Iron deficiency is the most common and widespread nutritional disorder in the world; 2 billion people — more than 30% of the world's population — are anemic, many because of iron deficiency. Iron deficiency is the only nutrient deficiency that is also prevalent in industrialized countries, particularly in women of childbearing age with heavy menstrual flow and miscarriages.
Serum Ferritin as Diagnostic Biomarker: Serum ferritin is considered the most accurate biomarker for the diagnosis of iron deficiency. Based on a systematic review conducted by Guyatt et al. to determine the diagnostic value of laboratory tests in the diagnosis of IDA, serum ferritin was found to be the most predictive and a better diagnostic test than mean cell volume (MCV) and transferrin saturation (TSAT). Serum ferritin values between 15–25 mcg/L were associated with a likelihood ratio of 8.83 for iron deficiency. Goodnough et al. found that a serum ferritin of less than 30 mcg/L was associated with a sensitivity of 92% for IDA and a positive predictive value of 83%.
Diagnostic Thresholds: Reference cut-off values for low serum ferritin have evolved and vary by guideline body. The current WHO serum ferritin thresholds for iron deficiency in children (<12 μg/L) and women (<15 μg/L) are derived from expert opinion based on radiometric assays in use decades ago. A clinical study of 228 outpatient subjects found that serum ferritin levels below 50 ng/mL establish the point from which the serum biomarker, the soluble transferrin receptor to hepcidin ratio, begins to correlate significantly with ferritin levels. Ferritin levels ≤50 ng/mL are indicative of early iron deficiency; hence, this should be considered as a clinically relevant cut-off for iron deficiency.
A systematic review of 29 clinical guidelines found that for the diagnosis of iron deficiency, a cutoff of 100 µg/L for serum ferritin concentration should be considered in most conditions and 20% for TSAT, except in particular situations, including young healthy women with heavy menstrual flow.
Complication of Inflammation: In the presence of inflammation, the concentration of ferritin is usually increased even if iron stores are low; hence, it can be difficult to interpret the true concentration of ferritin in situations where exposure to inflammation is common.
Research into phytoferritin as a dietary supplement form of iron has produced encouraging but still preliminary results in human studies.
Using in vitro digestion, researchers found that ferritin was relatively resistant against proteolytic enzymes. Binding of ferritin to Caco-2 cells was found to be saturable and the kinetics for binding characteristic for a receptor-mediated process. In human subjects, iron absorption from animal ferritin was similar to that from ferrous sulfate, suggesting that iron is well absorbed from ferritin.
Researchers did not find any significant difference between iron absorption from ferritin reconstituted with high-phosphate (plant-type) and low-phosphate (animal-type) ferritin mineral, suggesting that plant ferritin-iron is bioavailable. In a subsequent human study, iron from purified soybean ferritin given in a meal was found to be as well absorbed as ferrous iron. In conclusion, iron is well absorbed from phytoferritin and may represent a means of biofortification of staple foods.
However, there are important qualifications. Studies in women with low iron stores suggest a lower bioavailability (approximately 0.46) of iron from intrinsically labelled soybean when compared to FeSO₄. Other possible reasons for the relatively high bioavailability of ferritin iron in human subjects (30%–35%) could be the variations in gastric conditions and iron status prevailing in the study subjects.
A Caco-2 cell study of pea ferritin found important stability differences from soybean ferritin. The absorption was 26–40% worse than native pea ferritin not exposed to an acidic pH, which was instead absorbed into intestinal cells with the protein cage intact. Compared to ferrous sulphate, the native, non-degraded pea ferritin iron resulted in 60% fewer free radicals produced than ferrous sulphate. The non-degraded pea ferritin iron absorption was also unaffected by dietary chelators of iron.
Due to the exceptionally promising properties of ferritin and results of in vivo experiments on ferritin iron bioavailability, commercial production of nutraceuticals and bioactive food containing this protein may be expected soon. However, more studies are required to comprehend ferritin stability in the human digestive tract and during food processing, as well as more in vivo studies to understand the mechanism of protein absorption.
Evidence Assessment: Overall, the clinical evidence for phytoferritin as a dietary iron supplement is promising at the mechanistic and short-term absorption study level, but is still limited by relatively small human trials and questions of gastrointestinal stability. Long-term randomized controlled trials demonstrating sustained improvements in iron status are still needed.
Serum ferritin is classified as a marker of acute and chronic inflammation and is elevated in many inflammatory conditions, including rheumatoid arthritis, systemic lupus erythematosus, chronic kidney disease, COVID-19, acute infection, thyroiditis, and others.
Ferritin has emerged as a biomarker not only for iron-related disorders but also for inflammatory diseases and conditions in which inflammation plays a key role, including cancer, neurodegeneration, and infection.
If common clinical conditions can be excluded, clinicians must recognize hyperferritinemia as a clue to various autoimmune, inflammatory, and genetic disorders. Rare immune-mediated conditions such as hemophagocytic lymphohistiocytosis (HLH), where monocytes and macrophages seem to play a vital role through the production and release of ferritin, may cause extremely elevated ferritin levels.
Marked hyperferritinemia, defined as ferritin levels above 10,000 μg/L, can indicate severe underlying conditions, including infections, cardiovascular conditions such as heart failure, endocrinological, autoimmune, and malignancies.
Ferritin subfamilies — including the unbound, iron-free form of apoferritin, the iron-bound form of holoferritin, and ferritin itself — are composed of 24 subunits comprised of ferritin H-chains and ferritin L-chains with a hollow spherical cage. Not only does serum ferritin act as a critical marker of iron storage and delivery, but recent studies have also demonstrated that elevated serum ferritin levels are indicative of pathological processes in immunosuppression, angiogenesis, and proliferation. This evidence suggests that elevated serum ferritin could be a potential biomarker of malignant disease.
In clinical studies, the serum ferritin level has been correlated with the response rate to platinum-based chemotherapy in patients with advanced non-small cell lung cancer (NSCLC), and an elevated serum ferritin level was an independent prognostic factor for a poor survival outcome in patients with advanced NSCLC.
Serum ferritin is predominantly composed of L-chains under normal physiological conditions, whereas heavy ferritin and the ratio of H to L ferritins are increased in many malignant conditions. Although the mechanism remains unclear, studies have revealed that H-ferritin plays a role in malignancy, and it could be a potential biomarker to detect cancer.
Evidence Assessment: The association between elevated serum ferritin and cancer prognosis is based on observational and retrospective clinical studies. Causal relationships are not yet established; the elevated ferritin likely reflects systemic inflammation and tissue damage rather than a direct carcinogenic role of ferritin itself. Evidence is preliminary and correlational.
In kidney disease, elevated ferritin levels have been shown to be associated with increased mortality in three study regions covering Europe, Japan, and the United States, despite different median ferritin levels across regions. Clinical guidelines in heart failure and chronic kidney disease have adopted expanded ferritin thresholds. Studies in the setting of congestive heart failure have defined iron deficiency as a ferritin less than 100 mcg/L or a ferritin less than 300 mcg/L AND a transferrin saturation less than 20%.
In metabolic-associated steatotic liver disease (MASLD), biochemical evidence of excess iron, as indicated by elevated serum ferritin concentrations, is a common finding in approximately one third of patients. However, the elevation of serum ferritin in this context is recognized as a non-specific acute phase marker and does not necessarily reflect true iron overload.
Ferritin is directly involved in erythropoiesis as the primary reservoir of iron for hemoglobin synthesis. Low serum ferritin precedes the development of anemia, and the ferritin level is the cornerstone biomarker used to diagnose iron deficiency anemia across all clinical settings. While ferritin's primary roles are in iron storage and regulation, it has also been implicated in cellular defense, proliferation, oxidative stress management, and even disease progression.
Ferritin has been proven to be a marker of inflammation and the activation of M1 macrophages. Researchers have shown in mice that extracellular ferritin is likely to be released from macrophages via a non-classical secretory pathway rather than from damaged cells. During inflammatory states, ferritin rises as an acute phase reactant independently of iron stores, complicating its diagnostic interpretation.
The liver is the primary organ of iron storage and ferritin synthesis. Excess iron deposits in the liver, heart, and endocrine organs, where it promotes the generation of reactive oxygen species, resulting in oxidative stress, cellular damage, and progressive organ dysfunction. Elevated ferritin in the setting of metabolic liver disease frequently reflects both iron accumulation and hepatic inflammation.
Research has confirmed the discovery of receptors for H-ferritin in the body, including the brain, and has demonstrated that H-ferritin is the preferred manner of iron uptake relative to L-rich ferritin into all organs except for the liver. Iron is essential for brain development, myelination, and neurotransmitter synthesis; ferritin is the primary storage vehicle for this iron within neural tissue.
Both iron deficiency and iron overload impact cardiac function. Clinical guidelines recommend intravenous iron supplementation (monitored by ferritin) for heart failure patients with documented iron deficiency. Canadian Cardiovascular Society guidelines recommend consideration of IV iron therapy for heart failure patients with all of the following: ejection fraction ≤40%, serum ferritin <100 μg/L or between 100–299 μg/L, and TSAT <20%.
Chronic iron overload typically arises from hereditary hemochromatosis or repeated blood transfusions, especially in patients with thalassemia or sickle cell disease. Clinical manifestations vary with disease duration and severity, ranging from fatigue and arthralgia to life-threatening complications such as cirrhosis, cardiomyopathy, and hepatic failure.
Ferritin nanocage's good biocompatibility, low toxicity and immunogenicity, intrinsic tumor-targeting ability, high stability, low cost, and massive production potential together make it stand out from other nanocarriers.
Beyond conventional drug delivery, ferritin has emerged as a promising platform for vaccine development and as a scaffold to present peptides. By engineering ferritin to display antigenic peptides or proteins on its surface, it is possible to mimic the structural features of pathogens, eliciting potent immune responses and offering a novel approach to vaccination strategies.
Ferritin has been used as a scaffold for biomedical applications, especially for vaccine development against influenza, Epstein-Barr, HIV, hepatitis-C, Lyme disease, and respiratory viruses such as SARS-CoV-2. The remarkable stability, biocompatibility, surface functionalization, and self-assembly properties of ferritin nanoparticles make them very attractive platforms for a wide range of biomedical applications, including vaccine development. Strong immune responses have been observed in pre-clinical studies against a wide range of pathogens and have led to the exploration of ferritin nanoparticles-based vaccines in multiple Phase I clinical trials.
There has recently been an increased interest in ferritin-based vaccines, mainly due to their good immunogenicity and safety.
Ferritin as a supplemental or therapeutic agent exists in several contexts:
No established and universally agreed-upon supplemental dose of ferritin protein itself (as distinct from elemental iron) has been codified in pharmacopeial monographs or regulatory supplement guidelines. Phytoferritin-based products are marketed commercially, but the literature contains only small-scale absorption studies rather than dose-ranging efficacy trials.
Although physiologically necessary, excessive iron, whether acute or chronic, induces tissue injury and systemic toxicity, collectively called iron overload and toxicity. Iron overload denotes a chronic pathological state characterized by iron accumulation in parenchymal tissues, typically resulting from genetic mutations such as hereditary hemochromatosis or secondary causes that include repeated transfusions, chronic hemolysis, and excessive dietary intake.
Excessive iron levels can lead to toxicity by promoting the formation of free radicals through the Fenton reaction. In this reaction, ferrous iron (Fe²⁺) reacts with hydrogen peroxide, resulting in the generation of hydroxyl radicals and hydroxide ions, which can damage cellular components.
Iron overload, often resulting from hereditary conditions like hemochromatosis or chronic transfusion therapy, can lead to oxidative stress, tissue damage, and organ dysfunction. Excess iron accumulation in organs such as the liver, heart, and pancreas can cause serious complications including liver cirrhosis, heart failure, and diabetes, collectively known as iron overload disorders.
Many additional factors — including inflammation, infection, metabolic abnormalities, and malignancy — all of which may elevate serum ferritin, complicate interpretation of ferritin values. Serum ferritin is an acute phase reactant and a normal result does not exclude iron deficiency in the presence of coexisting infection, inflammation, or liver disease.
During inflammation, the expression of hepcidin is increased by cytokines. Consequently, hepcidin induces a functional iron deficiency characterized by high serum ferritin levels.
Iron supplementation of the human diet, especially with higher doses, brings a health risk, causing some gastric problems such as gastric upset, abdominal pain, and vomiting. Plant ferritin's protein coat may mitigate this. Intact pea ferritin iron is absorbed into intestinal cells by endocytosis, with its protein cage intact, and is less irritating to intestinal cells. However, this comparison is based on in vitro and small human absorption studies; large-scale tolerability data are not yet available.
Several inherited defects of the L-ferritin gene (FTL) can lead to either inappropriately high or low ferritin levels. These genetic hyperferritinemias — such as hereditary hyperferritinemia-cataract syndrome — can cause elevated serum ferritin without true iron overload, and must be distinguished from acquired causes.
Modifications to ferritin's surface for targeted drug delivery could introduce new immunogenic properties, warranting further investigation. This concern applies specifically to recombinant or chemically modified ferritin nanocages used in drug delivery or vaccine contexts, not to dietary phytoferritin under normal circumstances.
Acute toxicity often results from the ingestion of iron supplements, particularly in pediatric populations. While this risk is attributed to conventional iron salt supplements rather than food-form ferritin, it reflects the importance of monitoring total iron intake when ferritin-based products are used in combination with other iron preparations.
Health conditions that Ferritin may help support.
Body systems that Ferritin may help support.
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