Overview
This lecture covers dietary iron, including its physiological roles, sources, absorption, regulation, factors influencing requirements, and deficiency risks.
Iron Functions in the Body
- Iron is vital for oxygen transport via hemoglobin in red blood cells.
- Iron is essential for myoglobin, which stores and releases oxygen in muscles.
- It acts as a cofactor in enzymes for energy production, DNA/amino acid synthesis, hormone production, and immune function.
- Most body iron is found in hemoglobin, myoglobin, cytochromes, and storage proteins like ferritin and hemosiderin.
Iron Absorption and Regulation
- Iron is mainly absorbed in the duodenum and upper jejunum of the small intestine.
- Once absorbed, iron mostly binds to transferrin for transport to bone marrow.
- The liver stores excess iron as ferritin.
- Hepcidin, a liver-produced peptide, regulates absorption: more hepcidin means less absorption and more storage.
- The body controls iron levels by adjusting absorption, not excretion.
Dietary Iron Types and Sources
- Heme iron (from animal foods) is absorbed more efficiently (≈25%) than non-heme iron (from plants, ≈17% or less).
- Main heme sources: red meat, poultry, fish, shellfish.
- Main non-heme sources: legumes, dark greens, nuts, seeds, whole grains, fortified foods, eggs.
- Cooking in iron pots increases food iron content.
Factors Affecting Iron Absorption
- Vitamin C and the "MFP factor" (meat, fish, poultry) enhance non-heme iron absorption.
- Phytates (grains, legumes), polyphenols (tea, coffee, red wine), and calcium (dairy) inhibit iron absorption.
- Iron absorption from non-heme sources increases when iron stores are low.
- Plant-based diets require higher iron intake due to lower absorption.
Iron Requirements and Special Populations
- RDA varies: 0.27 mg/day for infants, 8 mg for adult men/postmenopausal women, 18 mg for menstruating women, 27 mg in pregnancy.
- Breastfed infants may need iron supplements starting at 4 months.
- Iron needs rise during growth spurts, menstruation, pregnancy, and in some health conditions.
- Malabsorptive disorders and GI surgeries can increase iron requirements.
Clinical Significance and Deficiency
- Iron deficiency affects over 1.6 billion globally, leading to anemia if severe.
- Risk is higher in women of childbearing age, children, and resource-limited regions.
- Iron toxicity is rare from food but possible from supplements or genetic disorders.
Key Terms & Definitions
- Heme Iron — Iron from animal sources, highly bioavailable.
- Non-Heme Iron — Iron from plant sources, less efficiently absorbed.
- Transferrin — Protein that transports iron in the blood.
- Ferritin — Protein that stores iron in cells.
- Hepcidin — Liver hormone that regulates iron absorption.
- RDA (Recommended Dietary Allowance) — Amount of nutrient needed daily for health.
Action Items / Next Steps
- Review iron-rich foods and dietary sources.
- Study factors that enhance or inhibit iron absorption.
- Check individual iron needs based on age, sex, and health status.