Iron Reserves in the Body
Iron reserves in the body are stored primarily in the liver, bone marrow, spleen, and skeletal muscles, predominantly as ferritin (70% in men, 80% in women) and to a lesser extent as hemosiderin 1.
Primary Storage Sites
The body stores iron beyond what is immediately needed for functional purposes in four main locations:
- Liver: The major storage organ for iron, containing the largest proportion of body iron reserves 1, 2, 3
- Bone marrow: Significant iron storage site supporting erythropoiesis 1
- Spleen: Important for iron recycling from senescent red blood cells 1, 2
- Skeletal muscles: Contains stored iron as myoglobin and other iron-containing proteins 1
Forms of Iron Storage
Iron is stored in two distinct protein complexes:
- Ferritin: The soluble protein complex that accounts for approximately 70% of stored iron in men and 80% in women. Small amounts also circulate in plasma and serve as a biomarker for iron stores 1
- Hemosiderin: The insoluble protein complex derived from iron-rich ferritin, representing the remaining storage iron. This form becomes more prominent when total storage iron exceeds 1,000 μg per gram of tissue 1, 4
Quantitative Distribution
The total body iron stores vary significantly by sex and age:
- Men: Store approximately 1.0-1.4 g of total body iron 1
- Women: Store approximately 0.2-0.4 g (lower due to menstrual losses) 1
- Children: Store even less than women 1
- Full-term infants: Born with approximately 75 mg/kg body weight, with iron stores contributing about 25% 1
Clinical Significance
When long-term negative iron balance occurs, iron stores are depleted before functional iron deficiency and anemia develop 1. This makes ferritin measurement crucial for early detection of iron depletion before it progresses to iron-deficiency anemia with its associated morbidity, including developmental delays in children and impaired work capacity in adults 1.
The liver's central role in iron storage also makes it particularly susceptible to injury from iron overload conditions like hemochromatosis, where excess hepatic iron can lead to fibrosis, cirrhosis, and hepatocellular carcinoma 5, 6.