Is zinc absorbed in ileum? A detailed look at mineral absorption

December 8, 2025 •

4 min read

After iron, zinc is the second most abundant trace element in the human body, but its absorption is a complex process influenced by many factors. While the duodenum and jejunum are traditionally considered primary sites, recent research confirms that zinc is absorbed in the ileum and throughout the entire small intestine. This distributed absorption ensures efficient nutrient uptake under varying dietary conditions and homeostatic demands.

Quick Summary

Zinc is absorbed throughout the small intestine, not just the upper sections. Absorption mechanisms and rates differ by segment, with the ileum playing a role, particularly in endogenous reabsorption and passive diffusion. Dietary factors, zinc status, and overall gut health heavily influence the mineral's bioavailability and absorption efficiency.

Key Points

Absorption Throughout Small Intestine: Zinc is absorbed in all three segments of the small intestine—the duodenum, jejunum, and ileum.
Diverse Mechanisms: Absorption occurs via both carrier-mediated, saturable transport and non-saturable passive diffusion, with the specific mechanism depending on zinc concentration and intestinal location.
Ileum's Role in Homeostasis: The ileum is an important site for reabsorbing endogenous zinc secreted into the gut, especially when proximal absorption is compromised.
Key Transporters: The ZIP4 protein is critical for luminal zinc uptake in the small intestine, while the ZnT1 protein exports zinc from the enterocytes into the bloodstream.
Dietary Influence: Dietary components heavily impact absorption; phytates inhibit it, while proteins and some amino acids can promote it.
Concentration-Dependent Efficiency: The body's fractional absorption of zinc is higher on low-zinc diets compared to high-zinc diets due to the saturation of transport systems.
Interference from Other Minerals: High doses of supplemental iron or calcium can interfere with zinc absorption, particularly when taken in concentrated forms.

The gastrointestinal tract is the central regulator of the body's zinc balance, managing the absorption of dietary zinc and the reabsorption of endogenously secreted zinc. A clear understanding of where and how this process occurs is essential for appreciating the complexities of micronutrient metabolism. While older studies pointed to the proximal small bowel (duodenum and jejunum) as the main site for dietary zinc, further research has revealed a more comprehensive picture.

The Small Intestine: The Primary Site for Zinc Absorption

Absorption of zinc takes place along the entire length of the small intestine, which consists of three distinct parts: the duodenum, jejunum, and ileum. Each segment, with its unique physiological environment and set of transport proteins, contributes to the overall process of mineral uptake, but their specific roles and capacities can differ.

Zinc Absorption Mechanisms

Zinc absorption involves at least two primary kinetic mechanisms, whose relative contribution changes depending on the concentration of zinc in the intestinal lumen:

Carrier-Mediated (Saturable) Transport: At normal, physiologically relevant concentrations, zinc is transported into the intestinal cells (enterocytes) by specific carrier proteins. This active transport pathway can become saturated if luminal zinc levels get too high.
Non-Saturable (Passive) Diffusion: At very high concentrations of zinc (such as from large supplemental doses), the passive diffusion pathway becomes more significant. Some research suggests it may be the dominant mechanism in the ileum, even at physiological concentrations.

Key Zinc Transport Proteins

Integral to this process are two families of zinc transporters, which regulate the movement of zinc into and out of the enterocytes:

ZIP Family (Solute Carrier 39A): These proteins increase the cytoplasmic zinc concentration by moving it from the intestinal lumen or intracellular compartments into the cell. ZIP4, located on the apical membrane of enterocytes, is a key transporter for dietary zinc uptake.
ZnT Family (Solute Carrier 30A): These transporters function to export zinc from the cytoplasm out of the cell or into intracellular vesicles. ZnT1, expressed on the basolateral membrane of enterocytes, facilitates the export of zinc into the portal blood.

Comparison of Zinc Absorption Across Intestinal Segments

There is some variation in absorption capacity and mechanism between the different segments of the small intestine.


Feature	Duodenum	Jejunum	Ileum
Primary Function	First site of absorption, sensitive to luminal conditions.	Often cited as having the highest rate of absorption in humans.	Active site for endogenous zinc reabsorption; uses non-saturable diffusion.
Main Mechanism	Carrier-mediated (saturable) at normal doses.	Predominantly carrier-mediated (saturable).	Non-saturable passive diffusion, particularly evident at physiological concentrations.
Capacity for Absorption	Important, but possibly lower rate than jejunum in humans.	High rate and capacity, especially for exogenous zinc.	Lower rate of exogenous absorption but potentially high capacity via passive diffusion, especially for reabsorbed endogenous zinc.

The Ileum's Specific Role in Zinc Balance

The ileum's capacity for absorbing zinc via non-saturable passive diffusion is critical, particularly for the homeostatic regulation of the body's total zinc. A significant amount of zinc is endogenously secreted into the intestinal lumen daily from sources like bile and pancreatic secretions. The ileum serves as a key site for reclaiming this vital mineral, preventing its loss in the feces. This is particularly important when small intestinal absorption is impaired, as studies have shown the colon (following the ileum) can increase its contribution in such cases. The long transit time in the ileum also supports this passive absorption mechanism.

Factors Affecting Overall Zinc Absorption

Many factors influence how much zinc is absorbed into the bloodstream.

Dietary Intake Level: Absorption efficiency is inversely related to intake; lower intake leads to higher fractional absorption.
Dietary Inhibitors: Phytates, found in grains, legumes, nuts, and seeds, can bind zinc and reduce absorption.
Dietary Promoters: Animal protein, amino acids, and citrate can enhance absorption by increasing solubility.
Mineral-Mineral Interactions: High doses of supplemental iron can interfere with zinc absorption. Supplemental calcium may also have a negative effect, especially with phytates.
Physiological State: Conditions like pregnancy, lactation, infancy, and certain GI disorders (e.g., Crohn's, celiac disease) impact absorption and requirements.
Zinc Status: Zinc-deficient individuals increase absorption efficiency via upregulated mechanisms.

Conclusion

In conclusion, zinc is absorbed in the ileum, alongside the duodenum and jejunum. While the upper small intestine is key for initial dietary uptake, the ileum's capacity for passive diffusion and reabsorption of endogenous zinc is crucial for maintaining overall zinc homeostasis. Dietary factors, transport proteins, and physiological state all play a role in this complex process.

For more in-depth information on zinc absorption mechanisms and homeostasis, refer to the review article: A Guide to Human Zinc Absorption: General Overview and Current Research.

Frequently Asked Questions

No, zinc is absorbed throughout the entire small intestine. However, the ileum is an important site for reabsorbing endogenous zinc that has been secreted into the gut from sources like pancreatic and biliary secretions.

Zinc is absorbed in all three parts of the small intestine: the duodenum, jejunum, and ileum. In humans, the duodenum and jejunum are typically considered the main sites for dietary zinc absorption.

Yes, absorption mechanisms vary. In the duodenum and jejunum, a carrier-mediated, saturable transport process is dominant at normal zinc concentrations. In the ileum, especially at higher luminal concentrations, non-saturable passive diffusion plays a significant role.

The ileum's role is crucial for zinc homeostasis. It acts as a site for the reabsorption of endogenous zinc that is secreted further up the digestive tract. This mechanism is particularly important when proximal absorption is limited.

The efficiency of zinc absorption is inversely proportional to the amount consumed. When intake is low, the body's homeostatic mechanisms increase absorption efficiency. Conversely, high intake saturates transporters and reduces efficiency, but increases total absorbed amount.

Phytates are compounds found in plant-based foods like grains, legumes, nuts, and seeds. They can bind to zinc in the digestive tract, forming an insoluble complex that is poorly absorbed, thereby reducing the mineral's bioavailability.

Yes, high supplemental doses of iron can negatively impact zinc absorption, especially when taken together on an empty stomach. The effect of supplemental calcium is debated, but may also interfere, particularly in the presence of phytates.

The main transporters are from the ZIP and ZnT families. The ZIP4 protein on the apical membrane is primarily responsible for absorbing zinc from the lumen into intestinal cells, while the ZnT1 protein on the basolateral membrane moves zinc out of the cells into the bloodstream.

Poor zinc absorption can result from dietary factors like high phytate intake, mineral-mineral interactions from supplements, or physiological issues. Gastrointestinal disorders like Crohn's disease, as well as bariatric surgery, can also significantly impair absorption.