What causes poor iron absorption from the gut?

October 14, 2025 •

4 min read

Iron deficiency is the most common nutrient deficiency in the world, affecting nearly 2 billion people globally. Understanding what causes poor iron absorption from the gut is crucial for anyone struggling to maintain healthy iron levels, as this can often be the root of the problem, even with adequate dietary intake.

Quick Summary

Several factors can hinder the body's ability to absorb iron, including the form of iron consumed (heme vs. non-heme), dietary inhibitors like phytates and calcium, and gut conditions such as celiac disease and H. pylori infection. The iron-regulating hormone hepcidin and certain medications can also negatively impact absorption.

Key Points

Dietary Compounds Block Absorption: Phytates in whole grains and legumes, and polyphenols in tea and coffee, bind to non-heme iron, preventing its uptake.
Heme vs. Non-Heme Iron: Non-heme iron from plants is poorly absorbed compared to heme iron from animal products like meat and poultry.
Calcium is an Inhibitor: Consuming calcium-rich foods or supplements with iron-rich meals or supplements significantly reduces iron absorption.
Gastric Acid is Vital: Medications like antacids and PPIs, which reduce stomach acid, can impair the conversion of iron to its absorbable form.
Gut Health Matters: Celiac disease, IBD, and H. pylori infection cause intestinal damage or inflammation that directly impedes iron absorption.
Chronic Illness and Inflammation: Systemic inflammation, triggered by chronic diseases, increases hepcidin levels, which reduces iron absorption and release from stores.
Nutrient Timing is Key: Separating iron-rich meals from foods and drinks that inhibit absorption, such as coffee, tea, and calcium, can improve uptake.
Enhancers can Help: Pairing iron-rich foods, particularly non-heme sources, with vitamin C-rich foods can counteract inhibitors and boost absorption.

The absorption of iron from our diet is a complex process influenced by a range of factors, from the specific chemical form of the iron to the presence of other compounds in our meals. When this process is disrupted, it can lead to a condition known as malabsorption, ultimately causing iron deficiency anemia.

The Two Types of Dietary Iron: A Crucial Distinction

There are two main forms of iron found in food, and your body absorbs them very differently.

Heme iron: This is the most easily absorbed form, derived from hemoglobin and myoglobin in animal products like meat, poultry, and fish. Absorption can be as high as 30% and is less affected by other dietary components.
Non-heme iron: Found in plant-based foods such as grains, beans, and fortified products, as well as in animal products like eggs and dairy. Its absorption is much lower (2-10%) and is significantly influenced by what else is eaten with it.

Dietary Factors that Inhibit Iron Absorption

Several common foods and drinks contain compounds that interfere with iron absorption, especially the less bioavailable non-heme variety.

Phytates: Found in whole grains, cereals, legumes, and nuts, phytic acid is a strong inhibitor of iron absorption. It binds to iron in the digestive tract, creating insoluble complexes that the body cannot absorb.
Polyphenols: These are natural antioxidants found in high concentrations in tea, coffee, cocoa, and wine. Like phytates, they form complexes with non-heme iron, reducing its bioavailability. Drinking coffee or tea with or immediately after a meal can decrease absorption by a significant margin.
Calcium: This mineral can inhibit the absorption of both heme and non-heme iron, though the effect is often most pronounced with supplements. For best results, calcium-rich foods like dairy products and calcium supplements should be consumed at a different time than iron-rich meals or supplements.
Certain Proteins: Some animal and plant-based proteins, such as those in soy and eggs, have been shown to have an inhibitory effect on iron absorption.

Medications and Gastric Health

The digestive process is delicate, and certain medications or conditions that affect the stomach and small intestine can seriously impede iron absorption.

Antacids and Acid-Suppressing Medications: Gastric acid is essential for converting iron into a form that can be absorbed, so long-term use of antacids, proton-pump inhibitors (PPIs), and H2 receptor antagonists can create an unfavorable environment for absorption. Case studies have shown that such medications can be directly linked to iron deficiency anemia.
Helicobacter pylori Infection: This bacterial infection can cause chronic gastritis, which reduces gastric acid output, thereby limiting iron absorption. H. pylori has also been shown to directly compete with the host for iron. Eradication therapy has been shown to improve iron status markers.
Bariatric Surgery: Procedures that reduce the size of the stomach or bypass sections of the small intestine can significantly decrease the surface area available for absorbing nutrients, including iron.

Gastrointestinal Disorders and Systemic Inflammation

Certain chronic health conditions directly damage the intestinal lining or disrupt the body's iron regulation, leading to malabsorption.

Celiac Disease: This autoimmune disorder is triggered by gluten and damages the lining of the small intestine, specifically the duodenum, which is the primary site of iron absorption. Inflammation and reduced surface area for absorption are key culprits.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis cause chronic inflammation of the digestive tract, impairing the body's ability to absorb iron.
Chronic Kidney Disease and Heart Failure: These chronic conditions can lead to an increase in the iron-regulating hormone hepcidin, which limits iron absorption and release from storage.
Genetic Disorders: Rare inherited conditions like iron-refractory iron deficiency anemia (IRIDA) involve genetic mutations that cause the body to improperly regulate iron absorption.

Comparison of Iron Absorption Inhibitors


Inhibitor	Common Food Sources	Impact on Non-Heme Iron	Impact on Heme Iron	Mitigation Strategies
Phytates	Whole grains, legumes, seeds	Strong inhibitor	Variable, some evidence	Soaking grains, sprouting legumes, combining with Vitamin C
Polyphenols	Tea, coffee, wine, cocoa	Strong inhibitor	Little to no effect	Consume between meals, not with them
Calcium	Dairy products, supplements	Inhibitory	Inhibitory	Take supplements and high-calcium foods separate from iron meals
Certain Proteins	Soy protein, egg whites	Inhibitory	Possible minor effect	Consume iron sources separately
Antacids	Acid-suppressing medication	Inhibitory	Indirectly inhibitory	Consult a doctor; manage timing
*H. pylori*	Bacterium	Significant, due to reduced acid	Significant, due to reduced acid	Eradication therapy

The Crucial Role of Hepcidin

Hepcidin is a hormone primarily produced in the liver that acts as a central regulator of iron absorption. Its main function is to control the release of iron into the bloodstream from intestinal cells and iron storage sites.

High Hepcidin: During infection, inflammation, or when iron stores are high, hepcidin production increases. This leads to the degradation of ferroportin, the protein responsible for transporting iron out of intestinal cells, and reduces iron absorption. This is often the cause of the iron deficiency associated with chronic diseases.
Low Hepcidin: When iron stores are low or the body needs more iron (e.g., during pregnancy), hepcidin production is suppressed. This allows more ferroportin to function, increasing iron absorption.

Conclusion

Poor iron absorption from the gut is not a single issue but a complex interplay of dietary habits, gut health, genetics, and medications. Identifying the root cause is the first step toward effective management. For many, simple dietary adjustments, like timing the consumption of coffee or tea away from meals, can make a significant difference. For those with underlying medical conditions such as celiac disease or H. pylori infection, addressing the condition directly is necessary to restore proper iron absorption. Given the complexity, consulting a healthcare professional or registered dietitian is highly recommended to develop a personalized strategy for improving iron status.

Frequently Asked Questions

Yes, coffee and tea contain polyphenols and tannins that bind to non-heme iron, significantly reducing its absorption. It is recommended to wait at least one to two hours after a meal to consume these beverages to minimize the effect.

Phytates, or phytic acid, are found in whole grains, legumes, nuts, and seeds. They form a strong bond with iron, creating an insoluble compound that the body cannot absorb in the small intestine. Soaking and sprouting legumes and grains can help reduce phytate content.

No, it is not recommended. Calcium can inhibit the absorption of both heme and non-heme iron. For optimal absorption, it's best to take calcium and iron supplements at separate times of the day.

Celiac disease is an autoimmune condition that damages the lining of the small intestine, particularly the duodenum, where most iron is absorbed. This damage leads to malabsorption, making it difficult for the body to absorb iron even with sufficient dietary intake.

Hepcidin is a hormone that regulates iron levels. During inflammation or when iron stores are high, hepcidin production increases. This hormone prevents the release of iron from intestinal cells and storage sites, effectively reducing iron absorption into the bloodstream.

Yes, gastric acid is necessary to convert non-heme iron into a more absorbable form. Antacids and acid-suppressing drugs like Proton Pump Inhibitors (PPIs) reduce stomach acidity, which hinders this process and can lead to poor iron absorption over time.

People following vegetarian or vegan diets are at higher risk for iron deficiency because they only consume non-heme iron from plant sources, which is less efficiently absorbed than heme iron from animal products. However, they can enhance absorption by consuming vitamin C-rich foods with their meals.

To improve absorption from plant-based foods, pair them with a source of vitamin C, such as citrus fruits, bell peppers, or tomatoes. Vitamin C helps convert non-heme iron into a more easily absorbable form.