What causes decreased iron absorption?

Causes of Decreased Iron Absorption

Several dietary and physiological factors can inhibit iron absorption, including polyphenols in tea and coffee, phytates in bran, calcium in dairy products, and certain medications, all of which can significantly impact iron status. 1

Dietary Inhibitors of Iron Absorption

• Polyphenols: Found in certain vegetables, tea, and coffee, these compounds can form insoluble complexes with iron, preventing its absorption 1, 2
• Tannins: Present in tea, these compounds can significantly reduce iron absorption by binding to iron and making it unavailable for uptake 1
• Phytates: Found in bran and whole grains, phytates can chelate iron and prevent its absorption in the gastrointestinal tract 1
• Calcium: Present in dairy products, calcium can compete with iron for absorption pathways, reducing overall iron uptake 1
• Coffee: Decreases iron absorption by approximately 54% and should not be consumed within an hour of taking iron supplements or iron-rich meals 3
• Matcha/Green Tea: Contains polyphenols that significantly inhibit iron absorption and should be consumed between meals rather than with meals for those at risk of iron deficiency 4

Physiological Factors Affecting Iron Absorption

• Iron Stores: The main factor controlling iron absorption is the amount of iron stored in the body. The gastrointestinal tract increases absorption when iron stores are low and decreases absorption when stores are sufficient 1
• Inflammatory Conditions: Chronic inflammation can increase hepcidin levels, which blocks iron absorption by preventing iron transport through ferroportin 5
• Gastrointestinal Disorders:
  • Celiac disease impairs absorption through damage to intestinal mucosa 6
  • Atrophic gastritis reduces stomach acid needed for optimal iron absorption 6
  • Inflammatory bowel disease affects 13-90% of patients with impaired iron absorption 6
• Surgical Procedures: Bariatric surgery, particularly procedures that bypass the duodenum and proximal jejunum where iron is primarily absorbed, significantly reduces iron absorption 1
• Acid-reducing Medications: These can decrease iron absorption by reducing the acidic environment needed to convert iron to its absorbable form 6

Medication Interactions

• Tetracycline Antibiotics: Iron supplements should not be taken within 2 hours of tetracycline antibiotics as they interfere with each other's absorption 7
• Antacids and Proton Pump Inhibitors: Reduce stomach acid production, which is necessary for converting dietary iron to its absorbable form 6

Enhancing Iron Absorption

• Vitamin C (Ascorbic Acid): Acts as a powerful enhancer of non-heme iron absorption by forming a chelate with iron and reducing ferric to ferrous iron 3
• Meat, Fish, and Poultry: Contain heme iron which is 2-3 times more absorbable than non-heme iron and also enhance absorption of non-heme iron 1
• Timing of Supplements: Taking iron on an empty stomach improves absorption; however, if gastrointestinal side effects occur, taking with food may be necessary 1
• Dosing Strategy: Taking iron supplements on alternate days rather than daily may improve absorption by allowing hepcidin levels to return to baseline 8

Special Considerations

• Pregnancy: Iron absorption increases during pregnancy, though the exact amount of increase is not well defined 1
• Infants: Young infants (<6 months) may have an immature homeostatic mechanism to downregulate dietary iron absorption when iron status is adequate, potentially making them susceptible to iron excess 1
• Elderly: Older adults often have decreased stomach acid production, which can impair iron absorption 6

By understanding these factors that decrease iron absorption, clinicians can better advise patients on strategies to optimize iron intake and absorption, particularly for those at risk of iron deficiency.