Where is iron found in the body?

December 14, 2025 •

3 min read

Approximately 70% of the body's iron is found in red blood cells as hemoglobin and in muscle cells as myoglobin, vital for oxygen transport and storage. The remaining portion is dispersed throughout various tissues, playing essential roles in metabolic processes and serving as reserves for the body.

Quick Summary

The majority of the body's iron exists in hemoglobin and myoglobin for oxygen transport, with stores primarily located in the liver, spleen, and bone marrow as ferritin and hemosiderin. Transport is facilitated by the protein transferrin.

Key Points

Bloodstream: Most iron is found in the bloodstream as a key component of hemoglobin in red blood cells, responsible for oxygen transport.
Muscles: Myoglobin, an iron-containing protein in muscle tissue, stores and releases oxygen for muscle function.
Liver: The liver is the main storage site for iron, where it is primarily bound to the protein ferritin.
Spleen and Bone Marrow: These organs also serve as significant storage sites, holding iron within macrophages and erythroid precursors.
Transport Protein: Iron is transported through the blood by a specific protein called transferrin, which delivers it to various tissues as needed.
Recycling: The body has an efficient recycling system, with macrophages processing iron from old red blood cells for reuse, maintaining iron balance.

The Distribution of Iron: An Overview

Iron is an essential mineral for numerous biological functions in the human body. An average adult typically has 3 to 5 grams of iron. This iron is distributed in both functional components and storage sites, regulated to support oxygen delivery, energy production, and cellular health.

Functional Iron

The largest portion of the body's iron is in the 'functional' pool, actively used in metabolic processes. This includes:

Hemoglobin: About two-thirds of total body iron is in hemoglobin within red blood cells, crucial for transporting oxygen.
Myoglobin: Found in muscle cells, myoglobin stores and releases oxygen for muscle activity.
Enzymes and Cytochromes: A smaller amount is incorporated into enzymes and cytochromes essential for cellular respiration and energy generation in most cells.

Storage Iron

Excess iron is stored to be used when dietary intake is insufficient. Key storage sites and proteins include:

Liver: The primary storage organ, containing hepatocytes and macrophages that store iron as ferritin and hemosiderin.
Spleen: Contains macrophages that process iron from aged red blood cells.
Bone Marrow: Stores iron, particularly in developing red blood cells.

Iron is stored bound to:

Ferritin: A soluble protein for readily available iron storage; serum ferritin indicates body iron stores.
Hemosiderin: An insoluble aggregate forming when ferritin capacity is exceeded.

Iron Transport

Iron is transported in the bloodstream by specific proteins:

Transferrin: This blood protein binds and carries iron to tissues, like bone marrow, after it's absorbed or released from storage.
Hepcidin: A hormone from the liver that regulates systemic iron balance by controlling iron release from storage and intestinal cells via ferroportin.

Functional vs. Storage Iron: A Comparison


Feature	Functional Iron	Storage Iron
Primary Location	Hemoglobin (red blood cells), Myoglobin (muscle cells), Enzymes	Liver, Spleen, Bone Marrow
Function	Oxygen transport, Oxygen storage, Cellular respiration, Energy metabolism	Iron reserve to be mobilized during deficiency
Key Proteins	Hemoglobin, Myoglobin, Cytochromes	Ferritin, Hemosiderin
Percentage of Total Body Iron	~70%	~25%
Availability	Actively and constantly utilized	Mobilized when needed, not constantly active
Form	Integrated into protein structures (heme groups, etc.)	Bound within protein complexes (ferritin) or aggregates (hemosiderin)

Iron Recycling

The body efficiently recycles iron, as it lacks an active excretion pathway:

Red Blood Cell Breakdown: Macrophages, mainly in the spleen and liver, break down old red blood cells after their 120-day lifespan.
Iron Scavenging: Iron is recovered from hemoglobin by these macrophages.
Transport: The salvaged iron is bound to transferrin and returned to circulation for delivery, particularly to bone marrow for new red blood cell production.

Recycling constitutes the majority of daily iron movement.

Iron Homeostasis Significance

Maintaining proper iron levels is crucial. Iron deficiency can cause anemia, leading to fatigue and weakened immunity. Excess iron, as in hemochromatosis, can damage organs like the liver and heart. Thus, balanced iron distribution and storage are vital.

Conclusion

Iron is distributed throughout the body for both immediate functional use and storage. The majority is in hemoglobin for oxygen transport, with substantial reserves in the liver, spleen, and bone marrow stored as ferritin and hemosiderin. Transferrin facilitates transport. This complex system of absorption, use, storage, and recycling efficiently manages this essential mineral.

For more information on iron metabolism, consult resources like the National Institutes of Health (NIH).

Frequently Asked Questions

The primary location of iron in the body is within red blood cells, specifically as a component of the protein hemoglobin, which transports oxygen.

Iron is stored mainly in the liver, spleen, and bone marrow. It is bound to proteins called ferritin and hemosiderin within the cells of these organs.

Approximately 70% of the body's total iron is found in the hemoglobin within red blood cells.

Once absorbed or recycled, iron is bound to a transport protein called transferrin, which delivers it through the bloodstream to cells that need it.

Yes, muscle cells contain iron as part of the protein myoglobin, which is responsible for storing and releasing oxygen for muscle function.

Ferritin is a soluble protein that stores iron in a readily available form. Hemosiderin is an insoluble aggregate that forms when ferritin's storage capacity is exceeded, indicating excess iron accumulation.

When red blood cells reach the end of their lifespan, they are broken down by macrophages in the spleen and liver. The iron is salvaged from the hemoglobin and reloaded onto transferrin for reuse.